How JustAnswer Works:

  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.

Ask Zaphod Your Own Question

Zaphod
Zaphod, Diagnostician, Trainer
Category: Car
Satisfied Customers: 33
Experience:  14+ years on an automotive technical hot line; Top Gun Diagnostician award
6510440
Type Your Car Question Here...
Zaphod is online now
A new question is answered every 9 seconds

jeep: carter y-s carb..engine starts and runs..runs well..back fire

Customer Question

I have an M-38 military jeep with a carter y-s carb. The engine starts and runs well up to about 1000 rpm. At which time it starts to break down and back fire. I have changed points, condenser, rotor, done compresson test 120 psi. New plugs, good wires. I understand this could be a problem with the carb. How do I rule this out. I cleaned it without improvement. Any ideas. Thanks peter XXXXXXX
Submitted: 2 years ago.
Category: Car
Expert:  Ridgerunnerras replied 2 years ago.

Ridgerunnerras :

Hello I would like to help you with this.

Ridgerunnerras :

I think this could be a problem with the fuel supply. I know that you said you clean your carburetor. Did you rebuild it or did you just clean it out?

Ridgerunnerras :
Ridgerunnerras :

You could also have a problem with your fuel pump or clogged fuel filter. If the float inside your carburetor is not set correctly the float bowl could be running out of fuel.


 

Ridgerunnerras :

I've also seen a symptom very similar to this on my boat and it was a bad ignition coil some of the oil had leaked out of the inside and a randomly stall out when the engine was running, but always start up and idle fine.


 

Ridgerunnerras :

What did you set to dwell to?


 

Ridgerunnerras :

Sorry ......what did you set the dwell to?


 

Ridgerunnerras :

If you would like any additional information or have more questions please don’t hesitate to ask!

Please remember to rate my answer "Great Service" This is the only way I will get compensated for my time helping you.


IF you feel the need to click either "Helped a little" or "I expected more", please stop and reply to me via the CONTINUE CONVERSATION button with the issue you have. I will be happy to continue further and do everything I can to provide you with the service you seek.


If you are having trouble with the site or rating system please let me know as this is a new feature and some Customers have had some trouble with it.


Thank you,


Carl,

Customer:

Carl, I dismantled the carburetor and cleaned all the elements to rule out any blockage. What problem with the fuel pump would cause the engine to loose power and backfire only on high rpm. I have a clear gas filter and will observe the fuel flow at high rpm. It somes on quickly, In other words, if I bring the engine up to the problem speed while standing still the breakdown in proformance is rapid. As I stated n the question, I installed a new fuel filter and lines. The question was mainly directed to the ys carter and is this problem indicitive of that unit?

Ridgerunnerras :

the Ys is a good carb I had on on my 68 DJ5 postal jeep I would look at you coil.


 

Ridgerunnerras :

Do you know what you set your Dwell At on you distributer?


 

Ridgerunnerras :

or maybe the float in the carb is set too low and the bowl is running dry.


 

Ridgerunnerras :

i do not think it is your carb unless the float is set incorrect

Customer:
Ridgerunnerras :

If you would like any additional information or have more questions please don’t hesitate to ask!

Please remember to rate my answer "Great Service" This is the only way I will get compensated for my time helping you.


IF you feel the need to click either "Helped a little" or "I expected more", please stop and reply to me via the CONTINUE CONVERSATION button with the issue you have. I will be happy to continue further and do everything I can to provide you with the service you seek.


If you are having trouble with the site or rating system please let me know as this is a new feature and some Customers have had some trouble with it.


Thank you,


Carl,

Customer:
Customer:

I changed coil, and dwell is set at 45 degrees, no improvement.


Peter

Customer:
Ridgerunnerras :

45 seem a bit hi try 31-34


 

Customer:

ridgerunneras,


 

Customer:

ridgerunnras, To date I gave followed all the advice given by just answer, Float set at 9/64 " from center seam of float to float chamber cover, dwell set at 20 thousands with dwell at about 38 degrees, spec. calls for 45 degrees but set lower as suggested. fuel filter new gas line rubber hoses new. when I drive the jeep. it runs like a clock until i get to 15 mph in first, 30 in second at which time it starts to break down and loose power. In 3rd gear if you give it full gas at 35 pulling a hill it will accellerate now problem you can feel the power and I assume this would be a period of high fuel consumpton which may rule out fuel supply. botXXXXX XXXXXne is what is causing high rev. breakdown?


 

Expert:  Walt-mod replied 2 years ago.
Hi,
I’m a moderator for this topic. Your Professional has opted out and I wonder whether you’re still waiting for an answer. If you are, please let me know and I will do my best to find another Professional to assist you right away. If not, feel free to let me know and I will cancel this question for you. Thank you!
Customer: replied 2 years ago.

Thank you,

 

  • I will assume you have read the problem and my attempts.
  • The botXXXXX XXXXXne is this:
  • after checking all aspects of the fuel, electrical and mechanical systems and replacing or refining the tuning the problem remains this:
  • When engine gets to 1100 RPMs it starts to break down. If you stay below this range it runs like a top.
  • It will pull a hill in high gear with no problem, for an engine with 60 hp. its exceptional. I have another M-38 and have driven it for over 12000 miles so I have a good idea what to expect.
  • Not sure about this carberator . I know it uses vaccume for two functions because its designed to operate under water. Is their a high speed jet that could cause this problem?
  • I am open to any specific suggestions.
  • thanks

Peter

Expert:  Zaphod replied 2 years ago.
Hi, and thanks for choosing JustAnswer. I'm Jeff and I'd love to help you with your Jeep. I would like to touch on three areas; ignition, fuel delivery and mechanical condition. If ignition is breaking down, if the car is leaning out the mixture [or not adding enough fuel under load] or lastly and least likely if the engine is weak.
Has the ignition system been ruled out as a culprit when it's missing, and how was this checked? If it hasn't here are two rather simple methods. The two methods can be jerry-rigged to be visible while you drive. Connecting a plain 12v test light between the coil negative and ground will get you a bright flash each time the coil is triggered. Erratic blinking indicates a triggering problem, such as loss of ground due to breaker plate wear or perhaps bouncing points. Points bounce can be enhanced by an excessive amount of freeplay in the distributor shaft either up and down or side to side. Turning the rotor back and forth should not cause the shaft to move up and down more than a noticeable bit. Sometimes the test light blinks too quickly, so the second method is to use an inductive timing light on the coil lead to the distributor, as well as each of the spark plug leads, and just observe the blinking. If either light is erratic when it's missing I'd look closely at this system. The blinking may speed up and slow down when it's missing but it should always be there. I doubt you have an ignition timing issue, but if you have a timing light you can mark the pulley in two spots and verify that it's stable for all four cylinders; another symptom of points bounce.
It's also possible that you have a lean condition. If it were a rich condition you'd see brown or black exhaust and the plugs would foul, making it tough to restart. A lean condition can be proven by adding fuel when it's missing. I've used a lot of methods, but the easiest, safest and most effective is by using propane. The "Propane Enrichment Kit" used for tuneups in the 1970's had a free flowing valve for standard 14 ounce propane bottles. A parts store may have one if you don't already. I 'made' one out of a propane torch I'd lost the orifice/filter for by leaving the nozzle off. A hose from the stem of either valve leading into the top of the carb will allow you to add small, large and huge [if you invert the bottle, the liquid propane vaporizes in the hose and the volume of gaseous propane delivered vastly increases] amounts of fuel. This can be used in a test bay or jerry-rigged to operate while driving. I've used this method often to move vehicles in the lot or even driving them short distances. If you add fuel and you get your 'zoom' back, the most likely culprit is the metering rod in the carb. It looks like a needle, and it's supposed to be pulled out of the main jet -effectively making the jet larger and increasing fuel flow - by a diaphragm. Venturi vacuum increases with airflow, this will be an internal passage. If the rod is stuck in the main jet, you'll have off idle and low speed cruise circuits but no real power or high speed cruise circuits.
Lastly I must touch on mechanical condition: your compression is borderline low. I'd like to see it closer to 145, but you may have some valves that haven't fully seated. I also need to mention checking for a restricted exhaust or foreign objects in individual exhaust passages if the manifold has been off: once upon a time several days were spent hunting down an intermittent miss in a 6 cylinder Jeep. A manifold bolt washer was hung up in #4 runner where it joined two other pipes, and it would intermittently flip sideways. I don't think this is the cause of your symptoms, I'd just like to see you get all the ponies you can.
I hope you can tell me more precisely what you've checked. If you run any of these tests I'd love to hear the results; or if you find the problem I'd really like to know what it was. I'll be waiting for your reply, Jeff
Customer: replied 2 years ago.

once again, am being very specific on what is going on. Not sure you can get a 1951 jeep engine to produce 145 psi compression, the electrical system is 24 volts and he the system is sealed to allow it to go under water. which make some tests almost impossible to do. My discussion with other people who tune these engines rule out fuel problems. The fact that I can lug the engine down and it still pulls tell us its not fuel. points are new that would tend to eliminate point bounce. Once again, It breaks down at 1100 RPMs weather on the road or in the shop.

thanks

Peter

 

PS I adjusted and checked all the lifters

Expert:  Zaphod replied 2 years ago.
Hi Peter, and thanks for getting back to me. I understand how your system is supposed to be sealed and the difficulties involved in checking anything. I don't, however, know if the systems are all intact on your vehicle-the few I see at the beach appear somewhat shredded but they're not looking to cross a river. In order to diagnose the symptom to the cause, we need to verify proper function of the engine, ignition and fuel systems-otherwise we're rowing in circles. Discussions do not verify system operation, tests and proper interpretation of their results do. Propane can be added virtually anywhere in the air intake system, it will verify or negate a fuel delivery or mixture issue quickly, and it's easier than trying to see the metering rod move or measure exhaust gases with an analyzer or by installing a two wire zirconia oxygen sensor. Lugging the engine, which is running at lower than optimal rpm, does not tell us anything about the high speed cruise circuit in the carburetor>the metering rod. The diaphragm can only be actuated if the passages are clear and the mechanism is free to move. The metering rod could be stuck in it's lowest position and you would, by nature of it's design, still have adequate fuel for low rpm operation. I've driven vehicles with the propane hose in the air filter housing, but since this breaking up takes place without driving it we don't even have to go that far; all you need is a torch with the nozzle removed [please don't lose the orifice or you'll have a collection of 'propane enrichment valves' like me]. Please look at the following image of the metering rod system adjustment and if possible perform this mechanical movement check [if you haven't already done this and you can get to it without much difficulty], and note the restrictions in the passages under the diaphragm :
graphic

New points may eliminate the bounce from a weak spring but not from other conditions previously mentioned, and it's not the only possible cause of intermittent or weak ignition operation. If you're absolutely 100% positive that there is nothing wrong with fuel delivery or the ignition system, the only other possibility is an engine mechanical issue. Please see the next two images, it is a Willys Technical Service Bulletin [TSB] issued in 1952 regarding complaints of stumbling or hesitating:
graphic

graphic

The first step implies a mechanical issue as a possible cause for your symptoms, as we're presuming fuel and ignition are in near perfect order, based on the compression specifications in this step versus your test results. To diagnose lower than normal compression readings I would want to repeat my compression test. This is the method I use: with the compression gauge installed, a battery charger connected and all the plugs removed, hold the release valve on the gauge and engage the starter. Allow the engine to build up to full cranking speed, and the cylinder under test to vent through the gauge's release valve. Once full cranking rpm is obtained, let the valve close right after the cylinder vents. Watch the gauge and note the readings on the next four compression strokes. A healthy cylinder should breach 75psig on the first stroke and hit at least 125 on the fourth. On a healthy engine it should seem as if you're always checking the same cylinder. If we're really close, then the next check is cylinder leakage. Cranking compression only tells us how well the cylinder can seal, it tells us nothing about the valve operation or if the engine is 'breathing' properly. A running compression test can reveal breathing issues such as worn cam lobes or badly coked up valves. At idle all the cylinders should reach the same pressure which will be much lower than the cranking test results due to manifold vacuum. If you snap the throttle fully open, the gauge should read the same as that cylinder finally measured for cranking: if it's lower then the valve train needs a closer look. Weak valve springs can allow valves to 'float' or close so slowly that the cylinder fails to pull in the air and fuel from the intake. If the pressure in the exhaust system is higher than the pressure in the intake manifold and both valves are open, there could be exhaust gases flowing backwards into the intake. Igniting the air and fuel in the intake can cause some pretty tremendous backfiring. Burning up all this air and fuel also means other cylinders will starve for fuel, exacerbating the poor running condition.
I truly hope you try some of the tests I've listed to solve your performance problem, and I really want to help so please let me know the results of any tests you have tried. Jeff
Customer: replied 2 years ago.

Zaphod, thanks for the great information.

Let me start by saying that early on in my tune up I found that #3 intake valve was not closing resulting in a cold compression of 70 Psi and hot test down to 50 psi. I concluded the lifter was adjusted to close. I found it had no gap with the valve closed. I adjusted it to 16 thousandents and the presure came up to 120 psi hot and cold with a dry test. What would cause the gap to close, assuming it was adjusted in the first place? That being said I believe one of the diaphrams may be too stiff from age or the new gas with alchol. I did check the metering rod and ball and cleaned along with the rest of the carb. I do not that the float bowl is loosing gas after sitting a few hours. It starts slow until the bowl refills, float level set at 9/64th. I changed out most of the ign. parts again for the 3rd time to rule out that factor. same results, engine looses power at 1100 rpms like clock work.

What do you think?

 

Peter

Expert:  Zaphod replied 2 years ago.
Hi Peter, and thanks for the update. My name is Jeff, "Zaphod" is just a screen name; when I signed on as an expert here I wasn't aware I'd be seen as Zaphod. Anyway - 0.016" is proper clearance cold for the intake valves, 0.018" is the exhaust setting. The clearance settings are necessary to ensure there's still some freeplay at operating temperature, when things expand due to heat. Exhaust valves run hotter so they expand a bit more, hence the larger gap. Having no clearance can prevent the valve from fully seating, and during combustion the flame can blast through the gap between the valve face and the valve seat eating away at the surfaces exactly like a torch. Light damage can be eradicated by seating the valves with valve grinding compound [silicon carbide granules mixed with grease]. Clover is the most popular brand and should be available at any auto parts store. Heavy damage usually requires replacing the valve; seats are incredibly hard and rarely damaged. My first car was a 1972 Toyota Carina, with their shrunken copy of half of Chrysler's Hemi in it. Shortly after my uneducated tuneup it burned two valves; when cranking it made ERRR ERRR TSSS TSSS noises and was nearly impossible to start. When the head came off, two exhaust valves were visibly burned allowing the compression to leak out and make the hissing noises. One had a very small crevice but another looked like a pizza with two slices missing. The 'crack' went all the way to the middle of the valve. Both seats cleaned up and the engine ran another 40,000 miles. I digress: this is about your vehicle. The increase in compression you obtained is a very good sign that your valve is now seating. Most if not all of the 'stuff' that had accumulated on the sealing surfaces will shortly be pounded away and your compression should improve unless there's more serious damage. Valve clearances can increase or decrease over time, even on the same engine. As the valve face wears out, the valve will be moving further into the head, raising the height of the valve stem under the rocker arm and thus reducing the clearance. This condition can be checked for by measuring the height of the installed valve, from the surface where the spring seats to the top of the stem. On the flip side, valve train clearances will increase as part surfaces wear: the cam lobe, tappets or lifters, pushrod ends, rocker arms at the ends and where it pivots, and the valve stem. Tiny bits of wear all over can add up to excessive clearance, loss of power and annoying tapping noises.
If the diaphragms are stiff they won't react properly and will eventually develop holes or tears. As the rpm increases, so does the airflow through the carb. If the diaphragm is stiff, it can't move the plunger and the metering rod can't be lifted out of the main jet which would allow it to add fuel for high speed operation. According to this page of YS data your float setting is spot-on:
"Carter YS Carbureter No. 950S
CARBURETER SPECIFICATIONS
For Willys 4 Cylinder Engine: 3 1/8 Inch Bore, 4 3/8 Inch Stroke

Dimensions: Flange size, 1 1/4 inch S. A. E.
Primary venturi, 11/32 inch I. D.
Secondary venturi, 19/32 inch I. D.
Main venturi, 1 1/4 inch I. D.

Float Setting: Distance from seam of float to float chamber
cover, with weight of float on needle and spring: 9/64 inch.

Vents: Balanced thru air horn to air cleaner via tubing external
to carbureter.
Vent: Bowl chamber to carbureter bore, size No. 68 (.031
inch) drill.

Gasoline Intake: Square vertical (spring loaded) needle No.
53 (.0595 inch) drill size in needle seat. Bleeder tube, as-
sembled over idle tube, with 2 side holes--No. 65 (.035 inch)
drill.

Low Speed Jet Tube: Jet size, No. 70 (.028 inch) drill (in end
of tube). Auxiliary jet (on side of tube) size: No. 75 (.021
inch) drill. By-pass (in air horn) size: No. 52 (.0635 inch)
drill. Economizer (in body) size: No. 54 (.055 inch) drill.

Idle Port: Upper port: slot type, length, .165 inch. Width,
.030 inch.

Idle Port Opening: Top of port--.125 to .129 inch above top
edge of valve with valve tightly closed.

Lower Port (For Idle Adjustment Screw): Size, .053 to .057
inch diameter.

Set Idle Adjustment Screw: 1/2 to 1 1/2 turns open. For richer
mixture, turn screw out. Idle engine at 700 R.P.M. with deep
fording vents open.

Main Nozzle: In primary venturi, angle 20°. Discharge jet size,
.0935 inch inside diameter. Main nozzle bleed (tube in air
horn) Size: No. 70 drill.

Metering Rod (Diaphragm operated): Economy step, .070 inch.
Power Step .054 inch diameter.
Vacuum passage restriction, size: No. 50 (.070 inch) drill
Vacuum passage bleed to bore, size: No. 65 (.035 inch) drill.

Metering Rod Jet: Size: .096 inch diameter.

Accelerating Pump: Diaphragm type, vacuum operated. Dis-
charge jet size, No. 72 drill. Intake ball check size: No. 40
drill. Discharge ball check under needle, size No. 50 drill.
Vacuum passage restriction, in flange size: No. 52 (.0635 inch)
drill. Vacuum passage air bleed to bore, size: No. 62 (.038
inch) drill.

Pump Stroke: No adjustment.

Choke: Manual--Offset, butterfly type with poppet valve.

Vacuum Spark Port: None.

Specifications come from a one page bulletin from Carter Carburetor Form 4960B released March 1953, revised March 1956."

One of the more annoying things about carbs is that the fuel in the bowl evaporates every time the engine is shut off hot. Heat dissipates [called heat soak] from the exhaust manifold and gradually boils off the more volatile components of gasoline in the carb. This wastes fuel and also pollutes the air, that's why newer vehicles had an evaporative emissions system.
If I was standing in front of your Jeep, I'd want to do two simple things. Pull off a plug wire and stick a spark plug [or spark tester] in the end, leave the plug sitting on the engine, watch the spark when it starts missing-it should always be there. Spark should be bluish-white, it should never be reddish or yellow. MYTH: the spark jumping the gap ignites the fuel. FACT: of the total amount of energy produced in the coil, only a portion is needed to jump the gap. The voltage needed is quite high, between 7,000 and 15,000 volts. The remaining energy that continues to flow across the gap for about 0.004 seconds is what ignites the fuel. This voltage is much lower, usually between 1,000 and 5,000 volts. K-D tools makes a spark tester that would be very useful here, part number 2757 for standard or points ignition systems [n the left] has a center electrode, the 2756 is for GM HEI and other electronic ignition systems [on the right] and does not have a center electrode:
graphic
Clipped to an engine ground and a plug wire, these will force the ignition system to use all the energy in jumping the gap so it's capabilities can be verified. Spark must be bluish-white, steady and consistent under all operating conditions Weak spark can't ignite lean mixtures very well - the fuel acts as a conductor between the spark plug electrodes. You can get effective results with points ignition by breaking the ground electrode off of a spark plug, though they're a bit difficult to clamp to ground. The testers are around $10 each. If spark is weak or intermittent, focus on the ignition system. There are other problems that might exist in the ignition system besides points, condenser, cap, rotor and plugs which are typical 'tune-up' parts. There is the coil, the associated wiring and ground connections; specifically the distributor ground for the points. Think about this: if the distributor ground is poor the coil won't be able to develop enough energy-this will become more evident as spark frequency increases. Changing unrelated parts repeatedly cannot cure the problem. The only way to be able to completely rule out an ignition system problem would be to change it entirely.
#2 on my quick test list is adding propane. This is probably the quickest and easiest way to find out if it is or is not a fuel related issue. You can look at the spark plugs to see what color the ceramic is for an overall mixture check: light reddish or tan is ok, dark brown or black indicates rich [or oil if it's slimy], white indicates lean [or new plugs that haven't been in long enough]. If you can set the throttle at a position where it's breaking up, add propane right at the entrance to the air filter housing. A plain old Bernz-o-matic plumber's torch will do fine. If you don't want to unscrew the nozzle and take out the orifice/filter [it looks like a small bolt in the end of the neck] we might be able to get enough propane by turning the torch upside down. If the engine smooths out and speeds up, focus on the carburetor as the cause. If there's no reaction and spark was ok, the next places I'd go are running compression, leakage/leakdown testing and checking the valve springs to see if they're weak. I really don't think you have a mechanical problem but I'm not known for guessing correctly 100% of the time: this is why I do testing. I can't emphasize enough the need to do testing in order to figure out what the cause of the breakup is. The 'shotgun approach', or 'well it might be this so let's change it' is only a proven method for wasting time and money. Please try the tests I've described, it can only help solve your problem. I'll be waiting for your reply, Jeff
Zaphod, Diagnostician, Trainer
Category: Car
Satisfied Customers: 33
Experience: 14+ years on an automotive technical hot line; Top Gun Diagnostician award
Zaphod and 3 other Car Specialists are ready to help you
Customer: replied 2 years ago.

Jeff.

I do believe I am getting close to a solution thanks to your very scientific advice.

#1 I did the Propane test with not change in engine operation,and did not loose any torch parts in the process.

#2 Spark test. This shows a very specific problem. At low RPM spark is good but not great color is good, however, as I increased the RPM to the point where it starts loosing power the spark is not longer visible. In other words the faster it turns the weaker the spark. I have another good running M-38 so I did the same test on it. The power of the spark on the good runner is about 3 times greater, good color and dose not diminish with speed.

You talked about distributor grounding. How is the distributer not grounded is my question? Is this a coil or a bad ground or both.

Thanks again

:Peter

Expert:  Zaphod replied 2 years ago.
Hi Peter, and thanks very much for the accept-it's greatly appreciated. Great job not losing any torch parts! Now we can thankfully leave the carb alone. If you need one, rebuild kits are still available 'out there on the internet'.
If the voltage supply to the coil drops off, or if the ground through the points is poor, we can't develop energy in the coil quickly enough. So, how to check points ground? We could try measuring resistance from the coil wire [disconnected from the coil] to the distributor housing and block [there may be a difference due to gum/varnish buildup]. This however only uses a tiny bit of energy - whatever is built into the meter - and not nearly what the system requires. An ohmmeter should indicate nearly zero ohms and tapping the closed points, breaker plate or housing should not disturb the reading. I would rather use a high current test more along the lines of what the points see every time they close. I often use a jumper wire and a headlight bulb for this type of test, called proving a ground. One headlight jumpered between battery positive and the distributor housing, as well as the breaker plate where the points are mounted, and perhaps even the points mounting plate in this case. This will run 4 to 6 amps through the ground paths. The headlight should be just as bright as when it's grounded to the block or battery. I really don't see the need to check new point sets, but you can use this test there also. If your grounds check out ok, I'd be highly suspicious of the coil.
I think it's great that you did these tests yourself and discovered what the real cause of the problem is. Your next mission, Peter, should you choose to accept it, is to unravel the mystery of the vanishing spark. Please keep me informed or your progress, you're doing very well so far. Jeff
Customer: replied 2 years ago.

Jeff,

As you know, this M-38 has a 24 volt electrical system. Not sure this has any bearing on our discussion, ground is ground. Next question. I have 4 used 24 v coils. How do I test them to determine if they are good? I did a resistance test and find that; 2, after market coils, have a primary resistance of about 6.5 when using the 200 ohms scale and the used old stock coils have about 12.6 ohms of resistance. I assume this is related to the amount or size of the wire in the primary. How do you measure the output of the secondary? Or do I go back to the old spark test of putting the output of the coil to ground and crank the engine.

Peter

PS what do you know about the operation of the old hit and miss engines? I just purchased a circa 1930 orchard sprayer with a Novo engine. No spark from the Magneto.

Expert:  Zaphod replied 2 years ago.
Hi Peter, that's good that you have spare parts. Coil primary resistance is, as you surmised, based on wire size and length used; it may differ from one coil manufacturer to another for the same application. To check the secondary, place one leat at the coil tower. The other lead can go to either primary coil, for example adding 6 or 12 ohms to 10,000 or thereabouts makes little difference. To test the output of a coil you need a coil tester or hook it up to a working system. These testers were part of old 1950's and 1960's engine analyzers. You could also build your own with a jump[er wire and capacitor [condenser]. The hard part about manually triggering a coil is breaking the connection quickly. I don't know if the company I worked for would have specs for your coil; Standard Motor Products used to make then in the Long Island City building where I worked for many years. They have a parts helpline still in place and the worst they can say is no. Their general number is(NNN) NNN-NNNN ask for Joey on the helpline, tell him Dr. Jeffreyo sent you. If anyone can dig up specs, "The Mushroom" can.
Oy, an orchard sprayer? Let me see what I can find out about magneto operation: i believe it's just a big magnet passing over a coil but I'm almost positive there's a point set in that contraption like older small engines [lawnmowers and such].
When you're checking spark output, the high voltage should be run through a gap of a specific size and then to ground. An adjustable gap spark tester will run you about $9, or you can rig something up with about a 1/4 inch gap for a points system. The spark at the gap should be bluish white.

I'll do some research on the magneto and get back here later today.
Jeff
Customer: replied 2 years ago.

Jeff.

It was mentioned to me this evening that they had a situation where the engine lost spark because the rotor shaft bearing was worn and caused a wobble as the rotor increased in speed.

Do you think this has any legs?. I do have a replacment bushing.

Peter

Expert:  Zaphod replied 2 years ago.
Hi Peter, yes it's possible; that would be the distributor shaft bearing/bushing. There should be only enough freeplay between the shaft and housing so that you can tell there is some; specs for one are 0.005-0.015 inches. Excessive freeplay causes variations in dwell as well as timing. If the freeplay were truly excessive - more than the height of the cam that actuates the rubbing block on the points - then it is possible that there would be too little dwell to create spark. With freeplay of this magnitude I would expect that the noise of the rotor tip whacking the electrodes in the cap either could not be heard or was ignored in favor of other attempts to solve the horrible running this would cause. I've seen rotor tips leaving marks in small areas on the inside of a cap, and while there was a small performance loss the complaint was the incredibly loud chirping.
Re-bushing a distributor isn't that difficult. I used to stress this to students>make permanent alignment marks on all the parts before they're removed, but now we can just take a bunch of digital pictures. I once got to find out how many ways you could put one back together.
I know this much about your Novo: I was at a antique/historical car show in...um...1982 and a guy had a hit and miss engine on a trailer. The flywheel was about 4 feet in diameter and it was really really slow. Once every 14 revs or so it fired-it was so loud it disturbed the show over a hundred yards away. Oh, and I once worked with a guy who grew up with farm equipment. You should really enter that as another question, I'm sure someone here knows about that system. I did some poking around in my library on magnetos and on the internet as well.
From what I've seen on magneto systems: if there's a coil it's a single winding or an adapted automotive using only the primary winding, and of low resistance; there may or may not be a battery; the magnet has to be rather strong; the trigger [some of the oddest 'points' I've seen] has to be timed properly.
Well, timing is one issue, just getting some spark is another. Keep me updated on the ignition system's health. Jeff
Customer: replied 2 years ago.

Jeff,


 


I do not think the play in the shaft is that excessive. In the middle of the night a question came to me. The capacitor for the coil may be from a 12 or 6 volt system, because the points for the M-38 are the same as a 6 volt CJ-3 which the M-38 is based on. Does capacitor voltage make a differance in their operaton?


 


I was told the a reason the Magnetos in a system, with no batteries like the vintage Novo, do not produce a spark is because tghe permanant magnet looses its power and has to be re magnetized.


 


Always great working with you,


 


Peter

Expert:  Zaphod replied 2 years ago.
Hi Peter, Capacitors [or condensers] have two specifications. One is the 'working voltage' and the other is it's capacity for storage. The latter is rated in Farads, typically millifarads or microfarads. If the working voltage of a cap is too low, it usually overheats and pops. If the capacity is incorrect in a distributor ignition system, the points will transfer metal in one direction or the other. If it shorts internally it will overheat and pop, if it burns open internally there will be lots of arcing at the points as in this case there is effectively no cap in the circuit.
Magnets will all lose strength with time, hot/cold cycles and vibration but they can be remagnetized. They can also be replaced with stronger magnets but this would be considered a modification and likely lower the value.
Jeff
Zaphod, Diagnostician, Trainer
Category: Car
Satisfied Customers: 33
Experience: 14+ years on an automotive technical hot line; Top Gun Diagnostician award
Zaphod and 3 other Car Specialists are ready to help you
Customer: replied 2 years ago.

Jeff,


 


My question is:


The ignaton system in the M-38 is a 24 volt system. The capacitor/ condenser I am using may be for a 12 or 6 volt system, because the points for the M-38 are the same as a 6 volt CJ-3 which the M-38 is based on. If I am using 6 volt ignation system condenser in a 24 volt system will it do the job or storing and releasing the load required?


You may be giving me the answer but I am not following.


 


Peter


 

Expert:  Zaphod replied 2 years ago.
There are two considerations concerning the capacitor/condenser; working voltage and storage capacity. The cap is there to absorb, or condense, the spike in voltage in the primary circuit that occurs at points opening. The spike voltage in an ignition primary circuit will easily reach 150v and may go as high as 300v. Caps for points ignition systems typically have a working voltage rating over 500v. If a cap with too low a voltage rating is used, it will pop as the voltage leaks through the layers, shorts the two conductors together and overheats the oil to it's boiling point. If the voltage rating is ok, but the storage value [the milli- or microfarad value] is off, then you will soon see metal building up on on half of the point set or the other. To visually see if it's working [I don't suppose you have a capacitor tester] crank the engine and observe the points as they open and close. Upon opening there should be just a tiny little arc. Disconnect the condenser and repeat the test, now you should see a rather large arc. If the arc is the same, suspect the cap/try another. The few ratings and test results I find place these in the 400-600v 0.20-0.30 microfarad range. Jeff
Customer: replied 2 years ago.

Jeff,


 


When I started this tune up I changed the Capacitor with a new one as stated above, When I had the problem I changed the new capacitor with another new one, same problem, I purchased a new coil last week tried it today, no improvement, reinstalled the old capacitor, Problem solved.


 


Thanks for all your help. Its been a great learning experience the trouble shooting you suggested will work on all old engines and will use it in the future and get rid of my shot gun.


 


Peter

Expert:  Zaphod replied 2 years ago.
Hi Peter, Congratulations on getting your Jeep back in running order. I'm really glad you feel this has been a learning experience. If, by any chance, the parts you bought were made by Standard Motor Products there may be some $ due to you. If the address on the box is 37-18 Northern Blvd, LIC, NY, 11101 it was, regardless of the brand name. If you return the part to the store, since it's obviously defective, they can exchange the part and help you file a labor claim. Standard will test the part and if it's bad they will pay you for having to re-diagnose the system. If your parts store is clueless, call the number I posted earlier and the operator will get you connected to the right person. It's been a pleasure helping you. I have learned that it is at the point where we presume something is not causal that our diagnostic efforts lose effectiveness. Enjoy your vehicle. Jeff
PS-if you ever plan cross a really really deep river, you might want to consider a scuba diver's emergency aid, an aerosol can sized "spare air" tank.
Customer: replied 2 years ago.

Jeff,


 


Not sure there is a problem with caps I think the ones I purchased were not correct for the 24V system in the jeep. The Scuba set up would be a good conversation piece. When people see the water level marks I painted on the Intake and Exhaust pipes thay ask how I could sit on the seat and drive with the water over the windshield. Standard answer is you stand up on the seat. I like your idea better.


 


Have a good 4th.


 


Peter

Expert:  Zaphod replied 2 years ago.
Don't forget a face mask or goggles. Jeff

JustAnswer in the News:

 
 
 
Ask-a-doc Web sites: If you've got a quick question, you can try to get an answer from sites that say they have various specialists on hand to give quick answers... Justanswer.com.
JustAnswer.com...has seen a spike since October in legal questions from readers about layoffs, unemployment and severance.
Web sites like justanswer.com/legal
...leave nothing to chance.
Traffic on JustAnswer rose 14 percent...and had nearly 400,000 page views in 30 days...inquiries related to stress, high blood pressure, drinking and heart pain jumped 33 percent.
Tory Johnson, GMA Workplace Contributor, discusses work-from-home jobs, such as JustAnswer in which verified Experts answer people’s questions.
I will tell you that...the things you have to go through to be an Expert are quite rigorous.
 
 
 

What Customers are Saying:

 
 
 
  • I would (and have) recommend your site to others I was quite satisfied with the quality of the information received, the professional with whom I interacted, and the quick response time. Thanks, and be sure that I'll be back whenever I need a question answered in a hurry. Stephanie P Elm City, NC
< Last | Next >
  • I would (and have) recommend your site to others I was quite satisfied with the quality of the information received, the professional with whom I interacted, and the quick response time. Thanks, and be sure that I'll be back whenever I need a question answered in a hurry. Stephanie P Elm City, NC
  • used your service this weekend with "Trecers" help. thank you ,thank you, thank you. replaced an A/C fan motor. Local Auto Zone had part. $15.00 "tracer" fee and $40.00 for parts, I saved several hundreds of dollers at a shop. i will recommend you and use you in the future. David L. Richmond, TX
  • 9 dollars, 2 hours of my time, and I drove away. Your diagnosis was right on the mark. Thank you so much. Phil Marysville, CA
  • Lurch. Thank you very much. I had real doubts about this website but your promptness of response, quick followup and to the point answer with picture was incredible. Charles Walnut Creek, CA
  • As a single woman, I really appreciate an excellent and affordable opinion.
    Thank you Geordie, I will not hesitate to contact justanswer in the future!
    Sue Charleston, WV
  • Another great insight to what may be the problem. I will have my mechanic take a look at it tomorrow. Thanks again, Frank...you do indeed know your stuff. Jim Castleberry, FL
  • Excellent reply, and also very quick. Really sounds like the Expert knows what he is talking about. I will be back to use your service when I need more help with my RV. Dutch USA
 
 
 

Meet The Experts:

 
 
 
  • Chris (aka-Moose)

    Technician

    Satisfied Customers:

    846
    16 years of experience
< Last | Next >
  • http://ww2.justanswer.com/uploads/MU/muddyford/2012-6-13_1204_1.64x64.png Chris (aka-Moose)'s Avatar

    Chris (aka-Moose)

    Technician

    Satisfied Customers:

    846
    16 years of experience
  • http://ww2.justanswer.com/uploads/TE/TedG/2012-6-15_14759_avaLarge.64x64.jpg Ted G.'s Avatar

    Ted G.

    ASE Certified Technician

    Satisfied Customers:

    1596
    20 years auto repair experience, ASE Master Tech, Mechanical Failure consultant, Expert Witness
  • http://ww2.justanswer.com/uploads/joecamel90/2008-11-13_03615_head_shot.jpg George H.'s Avatar

    George H.

    ASE Certified Technician

    Satisfied Customers:

    1311
    ASE Master Tech 15+ yrs, AAS Automotive Technology, Factory trained Asian specialist
  • http://ww2.justanswer.com/uploads/AM/amedee/2013-10-24_23656_Amedee1.64x64.jpg Amedee's Avatar

    Amedee

    ASE Master Tech

    Satisfied Customers:

    2367
    ASE Master Tech advanced level specialist
  • http://ww2.justanswer.com/uploads/SU/supermechanic/2013-8-23_03546_500.64x64.jpg Jerry's Avatar

    Jerry

    Master Mechanic

    Satisfied Customers:

    1906
    ASE master, 30+ years. All makes and models. Trouble shooter, shop forman, service manager
  • http://ww2.justanswer.com/uploads/CR/crzydrvr00/2013-11-3_12123_246347.64x64.jpg Richard's Avatar

    Richard

    ASE Certified Technician

    Satisfied Customers:

    942
    12 years Ford Lincoln/Mercury Jaguar dealership as a technician and shop foreman reparing all makes
  • http://ww2.justanswer.com/uploads/ST/Steve7654/2012-6-5_215929_japic800x660.64x64.jpg Steve's Avatar

    Steve

    Auto Service Technician

    Satisfied Customers:

    1980
    25+ yrs experience as a professional working technician; ASE L1 master technician
 
 
 

Related Car Questions