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 Dodgerench Your Own Question

Dodgerench
Dodgerench, ASE Certified Technician
Category: Dodge
Satisfied Customers: 3130
Experience:  30+ years Dodge/Chrysler exp., ASE Master with L1 certification. Driveability/ combustion specialist
4486286
Type Your Dodge Question Here...
Dodgerench is online now
A new question is answered every 9 seconds

1988 Dodge Ram 50: Misses..blows black exhaust..spark plugs

Resolved Question:

1988 Dodge Ram 50 - Misses terribly, and blows black exhaust until the engine warms up. I changed all the spark plugs, then found the #2 plug fouled, so I replaced it again. The problem persisted, so I changed the wires, dist. cap, and rotor.
There is no change in the problem. However, the engine idles and runs fine once it's warmed up.
Submitted: 7 years ago.
Category: Dodge
Expert:  Dodgerench replied 7 years ago.
Customer welcome to Just Answer. While there are a number of things that could cause your problem, all but one would continue on after the engine warmed completely.

It sounds like a choke problem. First remove your air cleaner lid and check to see if your choke blade moves freely (it's the butterfly valve at the top of the carburetor). It needs to move freely. If it doesn't, a few shots of carb cleaner, directed to the shaft area does wonders. Now working freely, start the engine (it will be somewhat flooded) and let the idle stabilize. Attempt to close the choke blade, using light finger-force. If the valve closes completely, with little or no resistance, there's more to the story. Your Mikuni carburetor uses what's called a choke breaker to crack the choke open after starting to prevent flooding. The exact amount of choke opening is critical to vehicle driveability; too little opening and you have flooding. Too much, stalling and hesitating until warm. Your breaker has probably failed completely.

They're simple units. A small diaphragn, with perhaps a little over a half-inch-square surface area. Attatched to it is a flat shaft, with a pivot on the end. A started engine applies engine vacuum to the diaphragm end. It's pulled in the direction of the vacuum, pulling the shaft along with it. The pivot then encounters a lever that's attatched to the choke shaft, opening the choke.

The problem is getting to them. It requires break-off screw and rivet removal, not a handy thing if you're not acquainted with Mikunis. If it proves true that you need a choke breaker and would like me to walk you through it, write me back. Otherwise, I strongly suggest trusting your '50 to a good mechanic.

I hope this has been helpful,Customerand thanks for using Just Answer!

Dodgerench, ASE Certified Technician
Category: Dodge
Satisfied Customers: 3130
Experience: 30+ years Dodge/Chrysler exp., ASE Master with L1 certification. Driveability/ combustion specialist
Dodgerench and other Dodge Specialists are ready to help you
Customer: replied 7 years ago.
Reply to Dodgerench's Post: Sounds like your on the right track. The engine is warm, and the choke blade freely opens when I close it by hand. Now to try it in the morning, when it's cold. Then I can tell if it's opening too much/soon.
I have to tell you, when I put plugs in about a month ago, I sprayed everything with carb cleaner, and then I moved (out of stupidity) the automatic choke adjuster a bit. Here in CA, I didn't think it needed to be closed so much.
Now, how do I know when I have it back to the correct/original adjustment. I can do it, but have no idea how to tell when it's correct, other than running it and then re-adjusting it, until it runs right.
Expert:  Dodgerench replied 7 years ago.
Customer I once again ask you... do you want to go down the rabbit hole? Mikunis scare the absolute begezzus out of most people. I've made a living out of these units, but most people... do not. It's a situation where I may be able to talk you though, but there simply are not enough pictoral aids to guide you through the mess that is... Mikuni hell.

Still interested? Let me know, and take a seat. This will take some time. I have a day job.

And I drive one these vehicles.

Customer: replied 7 years ago.
Reply to Dodgerench's Post: I'm not sure what I'm getting into, but neither am I afraid of it. I can follow instructions explicity, it's just a matter of how much you're willing to do.
I'm going to check the "Pay" button, wherever it is, so you get paid for your help. But, there may be more here than you're willing to do.
If you have any idea of where I could get the paperwork for this carb, and/or a rebuild kit, I'd really appreciate that info.
The truck started, lately, to develop a flat spot when first accelerating. So, I think it needs a kit, beyond fixing my 'screw up' stuff.
Thanks loads for your help.
Jim
Expert:  Dodgerench replied 7 years ago.

Jim, I like your style. We'll go into the choke breaker replacement, likely tomorrow. It's late and, sorry, the day job's a bit taxing sometimes. In the meantime, tell me about this hesitation. Is it just off-idle? Hard acceleration or just getting started? Hot/cold engine?By hesitation (by definition), you're experiencing something that causes a sudden, short decrease in available engine power, but then quickly returns? Or something else? Also, do you have a standard or automatic trans? At what altitude (approx) do you live/drive?

Another thing about Mikunis... at least at the factory level... they don't offer kits. Everything is a la carte. Gasket kit. Float kit (came with needle and seat). Shim kit (for adjusting float level. Accelerator pump diaphragm. Enrichment diaphragm. Choke breaker. Bowl vent package. Tamper-proof screws... the list goes on. Parts can easily exceed $300 and that was back in the old days. There might be a decent aftermarket kit available by now, but I just don't know.

If this is acceptable to you, Jim, expect a dissertation in Mikuni 101 tomorrow around dinnertime. Provided your hesitation problem doesn't require cracking the thing apart, I think you can probably handle it without a whole lot of trouble. Also, let me know... generally... what kind of mechanical aptitude you have. I don't mean to talk down to you, I just generally write in a manner that doesn't assume that the receiver has a whole lot of experience and include lots of detail, sometimes needless. It's never meant as a disrespect, I just tend to err on the wordy side. I look forward to working with you. Ed.

Customer: replied 7 years ago.
Reply to Dodgerench's Post: Hey Ed: Thanks so much for your time and info..
The hesitation happens any time I try to accelerate quickley. From the stop, at idle, it just seems to load up or something, then just catches and takes off. The same kind of thing happens if I'm driving and try to accelerate. It just stalls out for a few seconds, and then starts to catch up. There's no problem if it downshifts, which is frequently when stepping into the gas quite a bit. And, then it keeps going ok.
It seems to hesitate (that's my "stall") any time I step into the gas fast and somewhat hard.

Just a little about me, I was a tool maker previously, so I'm able to deal with most mechanical "things." I did rebuild a 4 barrel on my '78 Buick about a year ago, and I maintain my '75 Mercedes 450 SLC on my own. So, working on cars doesn't scare me, and I'm usually able to figure out 'most' things (other than this danged little Dodge).

I'll be watching for your reply. And, THANKS LOADS.
Jim
Expert:  Dodgerench replied 7 years ago.

Hi Jim, I'm back. I dug out the '88 D50 manual at work today and got a surprise. The carb you have isn't the same one that I expected. 1988 model year was a major departure from the earlier type, used for many years. While it's an upgrade from the earlier models, I don't have the depth of experience in this one last gasp of carburetion. It was simply a less-needy unit, so I didn't see enough of these units to create a lasting impression. That said, let's get started.

Choke operation and choke breaker condition remains the focus on the cold engine loading. The choke breaker just upgraded from a single diaphragm to a dual diaphragm assembly. The first half is active at all times, pulling the choke open immediately upon cold start by a measured amount (spec is about .100", not much). After coolant temperature reaches 65 degrees F, a thermovalve opens and applies vacuum to the upper chamber, further opening the choke blade (.130", measured at the top edge of the choke blade to the air horn). The two diaphragms are serviced as an assembly (part number MD617170) and come with new castings and springs.

Should you see no resistance to light finger pressure when attempting to close the choke blade, at least the lower breaker has ruptured. After 65 degrees, the second system tags in, so you might see some resistance at that point. Not good enough. You have to have the lower breaker working or the engine might not run long enough to get to the second stage.

Replacement appears to require removing the electrically-heated bimetal choke cap, located to the side facing the bulkhead. Tamper-proof screws will attempt to repel your efforts, possibly making carb removal necessary. The choke breaker shaft runs into the cavity covered by the choke cap and directly interacts with the linkages.

The breaker assembly (I apologize for the lack of visual aids) is located in a direct line from the bimetal cap to the vehicle right (toward the valve cover). It has a single vacuum hose connected to the outer 3-screw aluminum cast cover. The vacuum nipple on the cover has a single vacuum hose connected to it and has a vacuum delay valve cut into the hose about 4-5' away.

You may need to remove the secondary depression chamber to access the screws on the breaker assembly. The depression chamber, then, would be the large gold-colored thing (classic UFO shape) that has a link extending to the secondary barrel throttle shaft. Usually it only takes two screws to release it and it can just hang if it's sufficiently out of the way. A word of warning: Mikuni phillips-type screws are notoriously soft. They round easily. If you can catch any of these with a pair of battery pliers (my pref) or other strong-jawed plier, try to break them loose first. That way, you still have good phillips ends to work with later.

Once the three breaker screws are removed, tap on the assembly lightly and it'll fall apart. Make note of where the springs (I think there may be two) go. Remove the breakers, insert new. Initial adjustment of the lower breaker can only be done with the bimetal choke cap removed. With the breaker assembly screwed down tight, reach into the cap recess and move the breaker shaft to vehicle right (like it would do if vacuum was applied). You will also need to close the choke blade by hand. Measure the distance from the choke blade top to the carb air horn side. If your altitude is below 4000 feet, the factory adjustment will probably be OK. Above that... you might consider opening it another .010" or so.

The second stage can be checked by applying a vacuum source to the outer nipple. This should provide an additional .020" of kick (goes to about .130) and is adjustable by turning a set screw in the breaker outer casting (you'll see it). Backing it out increases travel, increasing blade opening.

Another note on carb removal, should it be necessary. You will need to drain some coolant, enough to get the level below the intake manifold surface where the carb bolts on. It has a coolant-heated base.

OK, hesitation. You say in your last post that it happens any time. Since the truck sounds pretty much undriveable until it heats up, that's where I'll concentrate the attention. Also, you state the problem passes and then it runs better, if not OK.

An immediate hesitatitation with rapid throttle movement is classic... lack of accelerator pumpitis. Your carb has two accelerator pumps. Lucky you.

The pump that you would call normal is the one that shoots a stream of fuel into the primary carb throat each time you open the throttle. A quick opening will produce a somewhat stronger stream, comparted to a slow roll-in. You can test for this by simply looking down the carb throat (engine off) and operating the throttle. Lack of a good, tight stream indicates something less than what you'd like. If it sprays in different directions, you have a blockage in the discharge nozzle. If the spray is erratic, not always appearing to start at the same throttle travel, a check valve internal to the carb is likely not sealing properly. Either way, there isn't much that can be done without carb disassembly. Pump stroke isn't adjustable on these units, either. Could be that the link fell off the throttle shaft-- they're held in place with a plastic grommet (tiny) and a small e-clip. The grommet could have disintegrated, eventually wearing away the clip (just a thought).

The second accel pump is for cold engine use only. It operates up to 65 degrees of block temperature, then shuts off. It's operated with engine vacuum, plumbed through a thermovalve that passes vacuum only to that temperature. An anaology: Imagine you're at a pinball machine. The ball rests on the plunger, waiting to be pulled back against spring pressure. Your hand in this case, becomes engine vacuum. Pulled back, the ball follows the plunger and waits. Releasing the plunger sends the ball shooting into the game, never to return again.

Engine vacuum (cold engine) is applied to the backside of a spring-loaded diaphragm. It causes fuel to be drawn into the chamber on the other side, where it sits, idle. A change in engine vacuum (acceleration) causes engine vacuum to drop, releasing the spring. Problem is, this applies only to cold engines and I'm not sure it applies.

All the engine sooting you've had might have had ill effects on the oxygen sensor. On your system, a failed sensor usually isn't detected by the feedback system. Rather, lack of a signal appears to be a lean mixture and may cause additional fuel to be dispensed.

Carb bowl vent failure can be a source of grief, too. Outside air pressure needs to be prevented from reaching the float bowl while driving, because the pressure differential between air cleaner and atmospheric can literally push fuel through the jets. Sometimes, just removing the air cleaner lid for a test drive is all it takes to tell if you have problems. Runs OK, bowl vent time. Not always, tho. The bowl vent is connected to the largest hose exiting the carb body, snaking its way across the valve cover to the vapor cansiter. With the engine running, disconnect the hose at the canister and attempt to blow through it lightly. If the bowl vent is working properly, nothing happens. Failed, it will be open and you'll flood and kill the engine. One other possibility is that vacuum may be applied to the carb bowl from a rotted bowl vent diaphragm. Vacuum is what's used to operate these units and if the vacuum makes its way to the bowl, it can have just the opposite effect--difficulty getting fuel through the jets. You may note a light vacuum on the hose, easiest with the hose in your mouth (yuk, I know). Ya duz wut ya has to duz sometimes.

I'll leave you with just this quick post for now. While more possibilities exist, they get difficult to test, long-distance. You still have EGR, feedback fuel controls, possibility of exhaust gas reversion from aspirator valves, throttle position sensor, timing (both cam and ignition) and other base carb problems to sort through. I surely wish you luck, Jim. Write back if we get close on something. Ed.

Dodgerench, ASE Certified Technician
Category: Dodge
Satisfied Customers: 3130
Experience: 30+ years Dodge/Chrysler exp., ASE Master with L1 certification. Driveability/ combustion specialist
Dodgerench and other Dodge Specialists are ready to help you

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 AM VERY GLAD THAT I TOOK A CHANCE ON YOUR PROBLEM SOLVING SKILLS. I WAS SUCCESSFUL IN REPLACING THE FUEL PUMP. MY TRUCK RUNS LIKE A CLOCK. IT RUNS LIKE THE DAY I BOUGHT IT. NO LUNGING FORWARD, THE TURBO REACTS THE SECOND I STOMP ON THE GAS, AND IT HAS A LOT MORE POWER AND EVEN SOUNDS BETTER TO ME. IT SAVED ABOUT $500.00 BY DOING THE WORK MYSELF. I GIVE YOU ALL THE CREDIT FOR YOUR DIAGNOSING THE PROBLEM, JUST FROM THE SYMPTONS I GAVE YOU OVER THE e MAIL. I WILL USE YOUR WEB SITE AGAIN AND REFER MY FRIENDS. THANKS SO MUCH FOR THE HELP. TOM WHITTAKER USA
< Last | Next >
  • I AM VERY GLAD THAT I TOOK A CHANCE ON YOUR PROBLEM SOLVING SKILLS. I WAS SUCCESSFUL IN REPLACING THE FUEL PUMP. MY TRUCK RUNS LIKE A CLOCK. IT RUNS LIKE THE DAY I BOUGHT IT. NO LUNGING FORWARD, THE TURBO REACTS THE SECOND I STOMP ON THE GAS, AND IT HAS A LOT MORE POWER AND EVEN SOUNDS BETTER TO ME. IT SAVED ABOUT $500.00 BY DOING THE WORK MYSELF. I GIVE YOU ALL THE CREDIT FOR YOUR DIAGNOSING THE PROBLEM, JUST FROM THE SYMPTONS I GAVE YOU OVER THE e MAIL. I WILL USE YOUR WEB SITE AGAIN AND REFER MY FRIENDS. THANKS SO MUCH FOR THE HELP. TOM WHITTAKER USA
  • Just a quick line to tell you how pleased I am to have my brakes working properly after all this time. Your answer was what I needed. I would certainly recommend you highly. God bless! Rev. Jerry Baysinger Holts Summit, Mo
  • I recently asked a question about my 2005 dodge ram, and I just wanted to let my Expert know that he hit the nail squarely on the head with his answer. I wanted to thank him again. Greg Pittsburgh, PA
  • Just a quick line to tell you how pleased I am to have my brakes working properly after all this time. Your answer was what I needed. I would certainly recommend you highly. God bless! Jerry Holts Summit, MO
  • I was skeptical at first but thought I'd give it a try. I was pleasantly surprised. Your site actually is a quality service that I would recommend to others in a heartbeat. Stan Sayre, PA
  • Wonderful service, prompt, efficient, and accurate. Couldn't have asked for more. I cannot thank you enough for your help. Mary C. Freshfield, Liverpool, UK
  • This expert is wonderful. They truly know what they are talking about, and they actually care about you. They really helped put my nerves at ease. Thank you so much!!!! Alex Los Angeles, CA
 
 
 

Meet The Experts:

 
 
 
  • Jerry

    Master Mechanic

    Satisfied Customers:

    1227
    ASE Master tech, 30 years exp. troubleshooter, driveability tech
< Last | Next >
  • http://ww2.justanswer.com/uploads/SU/supermechanic/2013-8-23_03546_500.64x64.jpg Jerry's Avatar

    Jerry

    Master Mechanic

    Satisfied Customers:

    1227
    ASE Master tech, 30 years exp. troubleshooter, driveability tech
  • http://ww2.justanswer.com/uploads/MO/MoparCertified/2012-6-7_4142_mechanic.64x64.jpg Mopar Certified's Avatar

    Mopar Certified

    Dodge Technician

    Satisfied Customers:

    5813
    24 Year Chrysler/Dodge Certified Specialist
  • http://ww2.justanswer.com/uploads/jeep10000/2008-9-18_222938_192601.jpg Chris's Avatar

    Chris

    Shop Foreman

    Satisfied Customers:

    4041
    ASE and Chrysler Certified Master Tech
  • http://ww2.justanswer.com/uploads/ke4ich/2009-08-12_212931_DSC02211.JPG moparfl's Avatar

    moparfl

    ASE Certified Technician

    Satisfied Customers:

    3285
    ASE Master Tech Gold level Chrysler Status 30 years dealership exp
  • http://ww2.justanswer.com/uploads/DO/dodgerench/2012-8-1_1142_IMG3173.64x64.JPG Dodgerench's Avatar

    Dodgerench

    ASE Certified Technician

    Satisfied Customers:

    2480
    30+ years Dodge/Chrysler exp., ASE Master with L1 certification. Driveability/ combustion specialist
  • http://ww2.justanswer.com/uploads/RO/rodcuda/2011-7-25_224114_Donhoff1.64x64.JPG Neal's Avatar

    Neal

    Dodge Mechanic

    Satisfied Customers:

    1870
    30 years experience in Dodge Chrysler and Plymouth
  • http://ww2.justanswer.com/uploads/tsmodie/2009-6-10_144056_tim.jpg Tim Mohr's Avatar

    Tim Mohr

    ASE MASTER TECH

    Satisfied Customers:

    1664
    30 YRS EXPERIENCE, FOREIGN AND DOMESTIC, GAS AND DEISEL