Hello I would like to help you with this.
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?
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.
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.
What did you set to dwell to?
Sorry ......what did you set the dwell to?
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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?
the Ys is a good carb I had on on my 68 DJ5 postal jeep I would look at you coil.
Do you know what you set your Dwell At on you distributer?
or maybe the float in the carb is set too low and the bowl is running dry.
i do not think it is your carb unless the float is set incorrect
I changed coil, and dwell is set at 45 degrees, no improvement.
45 seem a bit hi try 31-34
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?
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.
PS I adjusted and checked all the lifters
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?
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.
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.
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.
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.
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,
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.
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.
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.