Mikuni Parts help?

My baby is a 1987 Ram 50 with the stock 2.0L and Mikuni carb... The carb doesn't have anything printed or stamped on it that I can find except "Mikuni Corp". There are a number of other little problems with the truck, but this one is the most pressing at the moment.

1. Which Mikuni carb did the 2nd gen 2.0L come with?
2. Where can I find replacement parts without buying a whole new carburetor?

The accelerator pump has a hairline crack and the diaphragm is shot, and intermittently leaks fuel.

The truck also starts, idles, and seems to run fine, but randomly loses power. Initially, I thought it was simply the original coil and resistor, which I found and replaced using information from this forum, but she still sputters and loses power at random times. I'm hoping the accelerator pump is the other half of the equation, but I need to find a replacement to be able to test that hypothesis.

Any help at all will be greatly appreciated.

~Dr Steel

If the body of the carb is cracked, it can't be repaired. The resin they are made from doesn't accept any kind of adhesive or epoxy filler and there are only a few parts on them that are available new and 'can' be replaced. You will need to hunt down another carb from a JY - the carb itself is designated as a Mikuni 32-35DIDTA but there are a number of different variants depending on year and emissions requirements. These carbs are found on Mitsubishi vans as well but it will need to be from another 2.0 as the jetting from a 2.6 will cause it to run rich. If you haven't pulled apart a carb before, the Mikuni is either your worst nightmare or a perfect baptism of fire. Be aware that, if a carb you choose to use hasn't been apart for 15 years+, it will be due for an overhaul anyway as the diaphragms and seals are past their serviceable life.

Thank you so much, the body of the carburetor isn't cracked just the accelerator pump cover. I'm hoping I don't have to find a scrap carb just to get that part. Also where would I order a new accelerator pump diaphragm from? I tried through AutoZone and it was almost twice the size of the one I need.

Pump cover isn't a serviceable component so you need to do some JY diving for a replacement. They are all the same. If the accelerator pump diaphragm is tired you won't be getting a decent stream of fuel into the primary throat on open throttle take-off.

http://www.mightyram50.net/vbulletin...id=27256&stc=1http://www.mightyram50.net/vbulletin...id=27257&stc=1

As long as it's idling, it's fine... but if you rev it a couple times, it starts leaking.

What is this "JY"? The soonder I can find a replacement part and diaphragm, the better.

I appreciate your help

*Sooner. Allegedly, this carburetor and the fuel pump were replaced shortly before I bought it. Why he replaced it with the Mikuni is beyond me, but it's not in my budget to get the Weber conversion kit right now so I'm stuck trying to finagle this one.

Sometimes simple things go over my head. JY = junk yard :bang: I've checked the local salvage yards here, and none of them have the D50 or MM trucks so secondhand parts are nearly impossible to source locally.

I have a spare cover and diaphragm, both used and look okay. If you don't find anything near you, PM me an address and I'll send them to you.
Also, the carb number is printed on the top, air horn of the carb between the mixture control valve and the secondary throat. Remove the air cleaner and its rubber gasket to see it if it hasn't been rubbed off with age or removed by a rebuilder. Here's a pic of it:

http://www.mightyram50.net/vbulletin...id=27258&stc=1

If your carb has an electric choke, its number should be similar to that in the picture.

That is an odd looking carb. Fuel line going into the accelerator pump is from the top? And how the hell did the PO crack the damn thing? I have a bad feeling the guy put the diaphragm in the wrong way and torqued it til the cover bent and cracked. There is a possibility of internal damage too...

The Mikuni is a bit of an odd duck. The fuel line in Dr. Steel's pic is the tank return line. There is an inlet line to the pump reservoir not shown in his picture. It comes from the restricted port on the stock fuel pump. Not sure why the pump needs a separate inlet since there's an internal passage from the float bowl to the pump. Maybe it's to keep the pump charged when float bowl fuel levels are very low. Who knows the mind of Mikuni.

Got the parts, got them put in, and at least now she's not spraying gasoline out the side. But she's still sputtering when under load and sometimes she runs fine and I can get up to highway speed, but most of the time she won't get over 35. Acts like she's out of gas.

The fuel pump is new, the carb is new but the previous owner tried to "tune" it. Original ballast resistor went bad, replaced it with the one O'Reilly's said was correct which somehow killed the coil so I got the coil and resistor kit off eBay. New fuel filter as well. I need this truck to run well enough to get me back and forth to work until I can afford the Weber upgrade. Any advice on the multitude of adjustable screws? Or what to look for that I'm not thinking of. I'm not losing power all together, but I can't tell if it's not getting spark when it does it or if it's not getting fuel.

I forgot to mention, when it sputters, sometimes if I feather the throttle it recovers. Sometimes it makes it worse. If I floor it, it dies. I assumed since the accelerator pump was spraying fuel out the side when it would sputter that that was the problem. And while it does run a little better, the sputtering seems to be random and makes trying to go anywhere nearly impossible.

I'm at a loss and I don't have the money to do the Weber conversion. This carburetor was bought at the same time as the fuel pump by the previous owner.

Also, I try to run only non-ethanol.

It's like it's not getting enough fuel or not getting enough spark and I don't know how to diagnose which problem it is. So any help will be greatly greatly appreciated.

Sorry I keep posting multiple times but I keep remembering other details.

Another odd thing is that the choke doesn't open all the way. I have no clue how to adjust that. Maybe at highway speed it's not getting enough Air instead of not getting enough fuel?

Quote:

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Originally Posted by Dr Steel

Another odd thing is that the choke doesn't open all the way. I have no clue how to adjust that. Maybe at highway speed it's not getting enough Air instead of not getting enough fuel?

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If the choke isn't opening it will sputter from lack of air. It isn't really adjustable but with a fully warm engine, the choke butterfly should be completely open (vertical). If it stays mostly closed, check that the red wire to the choke has 12v while the engine is running. If not, check the wire on both sides of the eight-pin connector, and then the same red wire at the choke relay and the black/white wire to the choke relay. The relay is in the "device box" attached to the driver's side wheel well.

Check the accelerator pump operation. Remove the air cleaner top with the engine not running. While looking down into the primary throat, quickly open the throttle linkage. You should see a small stream of fuel squirt down into the primary venturi. If nothing or it only drips some, the accelerator pump circuit is obstructed and that can cause the drivability issues you described.

Lastly, with the exception of the idle speed screw, resist the temptation to adjust any of the other screws. Most are set at the factory (or by a rebuilder). "Adjusting" them can make matters worse at this point.

If the engine is hot and the choke doesn’t open. The thermal wax is bad and you can’t get that anymore. But if it idles ok and just dies when trying to get up to speed. It can be the fuel filter or the coil.

The accelerator pump only works from closed to open throttle - literally just a single shot of fuel to stop it from stumbling on a lean fuel mix. Don't go messing with the screws on the linkages. There are fast idle adjustments and choke settings affected by them and not knowing when or how to adjust them can turn ugly. Resetting the choke butterfly spring tension on the thermal wax pellet choke takes near superhuman strength to override the main loading spring and can crush a finger lol (and that is only IF you are able to get the anti-tamper screws off it to make the necessary adjustments). The actual wax pellet 'is' still available but you will have nearly zero chance of successfully installing one. *extra tip on the wax pellet choke - if you see a thick looking grease built up around the actuator rod on the choke assembly, that is the wax that is meant to be inside it and it has failed. Yes - the Mikuni is a BIATCH

Quote:

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Originally Posted by FMS88

If the choke isn't opening it will sputter from lack of air. It isn't really adjustable but with a fully warm engine, the choke butterfly should be completely open (vertical). If it stays mostly closed, check that the red wire to the choke has 12v while the engine is running. If not, check the wire on both sides of the eight-pin connector, and then the same red wire at the choke relay and the black/white wire to the choke relay. The relay is in the "device box" attached to the driver's side wheel well.

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There is definitely some minor issue with the choke. I'll have to check the electrical stuff after work. It only opens 3/4 of the way. I can move the plate all the way open, but it gently springs back to three quarters open as soon as I let go of it. It shouldn't be the wax pellet issue, because the carburetor is less than 2 years old. Previous owner bought a brand new mikuni and fuel pump, it still couldn't get it running the way he wanted it after screwing with the settings on the carb. It ran fine until the original resistor failed, but it never ran optimally as long as I've had it.

Quote:

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Originally Posted by FMS88

Check the accelerator pump operation. Remove the air cleaner top with the engine not running. While looking down into the primary throat, quickly open the throttle linkage. You should see a small stream of fuel squirt down into the primary venturi. If nothing or it only drips some, the accelerator pump circuit is obstructed and that can cause the drivability issues you described.

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I'll double check this as well, but it should be functional now unless there's a clog between the pump and the throat.

Quote:

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Originally Posted by FMS88

Lastly, with the exception of the idle speed screw, resist the temptation to adjust any of the other screws. Most are set at the factory (or by a rebuilder). "Adjusting" them can make matters worse at this point.

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Unfortunately, previous owner already fubar'd that for me. I need to find out what the stock settings are on all the screws so I can get it back to spec.

Quote:

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Originally Posted by camoit

If the engine is hot and the choke doesn’t open. The thermal wax is bad and you can’t get that anymore. But if it idles ok and just dies when trying to get up to speed. It can be the fuel filter or the coil.

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Fuel pump and carb were less than 3 months old when I bought the truck, but unfortunately the previous owner did try to "tune" the carb. I replaced the spark plugs, filters, & fluids within a month of buying it, and recently replaced the coil and resistor, as well as replacing the fuel filter again. Last night I bypassed the factory fuel filter setup, as well as taking a small piece of partially kinked line out, and put a clear glass fuel filter in the line right before the fuel pump under the hood. I haven't taken her out on the highway again since, but that did get me home last night.

Quote:

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Originally Posted by geezer101

The accelerator pump only works from closed to open throttle - literally just a single shot of fuel to stop it from stumbling on a lean fuel mix. Don't go messing with the screws on the linkages. There are fast idle adjustments and choke settings affected by them and not knowing when or how to adjust them can turn ugly. Resetting the choke butterfly spring tension on the thermal wax pellet choke takes near superhuman strength to override the main loading spring and can crush a finger lol (and that is only IF you are able to get the anti-tamper screws off it to make the necessary adjustments). The actual wax pellet 'is' still available but you will have nearly zero chance of successfully installing one. *extra tip on the wax pellet choke - if you see a thick looking grease built up around the actuator rod on the choke assembly, that is the wax that is meant to be inside it and it has failed. Yes - the Mikuni is a BIATCH

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I don't see any gunk around the choke linkage... But that's what I was afraid of on the settings since the previous owner admitted to trying to tune it.

I didn't fiddle with the screws on the carb but the previous owner did unfortunately. I would like an option besides having to buy a whole new carburetor... If I could get a hold of the original owner I would ask him to do a warranty swap but when I left Kansas I lost contact. I don't really want to fiddle with the settings on it, but if nothing else works I'm going to have to or have someone more knowledgeable do it. And I thought my quadrajet on my old C10 was a PITA.

Quote:

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Originally Posted by Dr Steel

There is definitely some minor issue with the choke. I'll have to check the electrical stuff after work. It only opens 3/4 of the way. I can move the plate all the way open, but it gently springs back to three quarters open as soon as I let go of it. It shouldn't be the wax pellet issue...

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Mitsubishi went to an electric choke for the 87-89 model years. If the firewall side of the carb looks like this, there's no wax pellet to worry about:

http://www.mightyram50.net/vbulletin...id=27281&stc=1

If the choke butterfly is mostly opening, it's probably not the issue. But to be sure, you can temporarily "fix" it in a fully open position. With engine off and air cleaner removed, manually open the throttle so you can move the butterfly to the fully open position. Then jam a piece of wood, rubber or plastic into the space circled in this pic:
http://www.mightyram50.net/vbulletin...id=27282&stc=1
Make sure the butterfly is nearly immobilized in the open position and that the jam piece won't interfere with installing the air cleaner and its gasket. Install the air cleaner and test drive it. If it still has drivability issues when hot, it's not the choke. Then check the accelerator pump operation, if you haven't already.

One other remote possibility - if the PO replaced the fuel pump, check that its output lines are properly routed. One FP output port is restricted; that line should go to the accelerator pump. The unrestricted line goes to the float bowl. If reversed, the engine can be starved for fuel under certain conditions.

FSM has got this :thumbup: