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Thread: Mikuni Trouble: Bowl Vent Diaphragm

  1. #1

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    Richland, WA
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    1988 Dodge Ram 50
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    4G63

    Mikuni Trouble: Bowl Vent Diaphragm

    Hello,

    I just bought my first Ram 50 a month ago. It's a 1988 with a 5-speed and the 2.0 L. It's also got the stock Mikuni carb.

    It was running fine, and then not--it really started to sound lousy, running rough and hesitating. After a lot of research, I had the problem about 80% diagnosed as a bad bowl vent diaphragm. After DAYS of searching, I was finally able to locate one of these diaphragms over the internet. It's a little rubber ring on about a 3" shaft, and "pops" out of the carb sort of like the axle on a front-wheel-drive car. Anyway...

    The new part arrived today, but when I tried installing it, I encountered resistance. Turns out the gasket on the receiving end (DEEP in the carb!) had become unseated, and was rattling around loose--thus, it wasn't grabbing the shaft like it should, and me forcing the shaft in was only making things worse.

    It seems like my only options now are to A) take the carb completely apart, hoping to re-seat the gasket, or B) take it to a shop and throw money around. I hate to do the latter, but I've never opened a carb before and I'm not sure I'd be able to get it back together. Help!

    Thanks,
    Adam

  2. #2



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    1986 Mitsubishi Mighty Max
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    Adam, you live in Washington as myself does. If your going to throw money, Throw a 32/36 weber on it. You have no more smog checks on your truck and we are exempt. Enjoy some extra power and a better carb. Those Mikuni carbs are pretty much garbage once they go bad. The weber will also relieve you some of the other smog stuff.


    Welcome to the Forum also.

  3. #3

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    Thanks for the welcome. I've thought of going the Weber route, but hate to throw money, as you say. I've also heard (on this forum) that buying a Weber also means buying a fuel pump, regulator, etc., which adds up. I just need to figure out if the cost of a Weber is a better return that the cost of a Mikuni repair, which could be anything.

  4. #4

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    Adelaide, South Australia
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    1985 Mitsubishi L200
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    Welcome to the site AdamW. If you've never pulled apart a carby before my recommendation would be to source a reasonably good second hand unit, get a manual and pull it down on a nice open bench that won't get disturbed in a hurry. It's too risky to take apart the only carby you've got and end up getting stranded. The Mikuni's are not the most forgiving thing to disassemble but if you pay attention and ask for advice, you'll be able to work through it. They are nicer to work on than a Nikkei or a Hitachi carby (both of which have some nasty design issues) but they are complex. Oh, and get your hands on a rebuild kit too - there's no point in taking one of these things apart and trying to re-use junk gaskets, seals and diaphragms. It'll grief you no end... Good luck.

  5. #5

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    I appreciate the advice. I actually managed to install the new bowl-vent diaphragm, which was nice, and when I tested it all seemed well. (Disconnect vacuum hose running from vapor canister to carb, at the canister, and blow through it--if you hear air running through to the carb, the diaphragm is shot. I heard air with the old part, but not with the new one!)
    So I was very surprised when that didn't do anything to fix the problem--the truck still runs poorly, with much hesitation and vibration throughout the drivetrain. The shift knob and cab shake so much I'd be sure it was a loose mount somewhere, if not for the poor performance. Though the engine at idle doesn't sound too bad--only when driving does it really bog down. Maybe it could be as simple as a bad fuel filter or something along the line. I guess I'm back at square one!

  6. #6



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    If you have the g63b motor, it could be that the timing belt skipped a tooth or lost one or more. Check out the filters, all the vacuum lines, especially the ones going into the metal box on the drivers side inner fender. A vac leak will cause that poor performance and shaking.
    Pennyman1
    The best Dodge that Dodge never made
    Living the D-50 lifestyle since 1980

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