MC2100 leaking gas out top, help please - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 04-12-2007, 11:20 PM Thread Starter
Sawzall Poster Boy
 
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MC2100 leaking gas out top, help please

I know this is kinda OT but jeep used the same carb, it's '76 bronco, stock mc2100/ 302. The truck sat for 2 years then I got it, poured gas down the carb it started right up. I don't think this happened the first couple times then all of a sudden it started "flow" (it wasn't a drip and it wasn't shooting like crazy) gas out the 2 vents on the top front of the carb where the air cleaner mounts. I went and had a buddy that's pretty good with carbs re-build it. Still does it, I tried different float levels, it still does it. I haven’t touched the idle screws because it idled fine before I re-built it. Any ideas?

Would a vacuum line in the wrong spot do this, I did mess with the vacuum lines. Is there any way the stock mechanical fuel pump could be feeding it way too much fuel? I know almost nothing about carbs please help; I’m trying to take the thing wheeling Saturday.

Thanks,
Andy

Last edited by barrelroll; 04-12-2007 at 11:25 PM.
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post #2 of (permalink) Old 04-13-2007, 12:14 AM
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It's probably the wrong needle seat. I just rebuilt mine and the kit had the wrong seat and it did exactly what you describe. In my case the seat was too high not allowing the needle to seat properly because the float hit the top gasket before the needle was seated.

I messed w/ my float for awhile then just reused the old seat and everything was good. I used a generic kit from Autozone and just guessed on the year of the carb.

John

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post #3 of (permalink) Old 04-13-2007, 12:42 AM
 
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Same thing will happen if you have ANYTHING in the fuel line...
You need a GREAT BIG HONKIN' FUEL FILTER just as close to the carb as you can work it in.

You also need to flush the line before you hook it up to the carb.
Scale off the inside of the short line is enough to foul up the needle and seat... (just went through that on the trail with a guy)
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post #4 of (permalink) Old 04-13-2007, 06:13 AM Thread Starter
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It's got the factory filter right at the carb and then about 6" back one of the clear plastic filters about the size of a lemon. I guess i'll try flushing her out and adding a second. Could a fuel pressure regulator solve my problem?
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post #5 of (permalink) Old 04-13-2007, 06:35 AM
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I used to have a MC2100 on my Waggie and it used to do the exact same thing. My guess is that the needle is not setting down all the way and you are getting fuel pumped into the bowl when it shouldn't be. Could be that you have some crud in there, or you may need to adjust (bend) the linkage a bit. Another thing that would cause this problem (this is what was wrong with mine) is that you may have a hole in your float. Mine had a small pin hole so that fule was getting inside it. Once it was about 1/2 full of fuel... it no longer floated, and so it never set the needle down all the way...
Those are a few things you may want to check out.

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post #6 of (permalink) Old 04-13-2007, 06:55 AM Thread Starter
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Ok, so this sounds like too low or too high of float problem, I'm caburator retarted do I want it sitting lower or higher in the bowl. When we rebuilt it it was set pretty low compared to the specs and we split the differance between the spec and where it was. Since then there's been no method to the madness. I just missed a fricken field trip I was susposed to go on today for school so atleast I have time to work on the pile.
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post #7 of (permalink) Old 04-13-2007, 09:32 AM
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It may be that the float has sunk. If it's brass there may be a pinhole in it, filling it with fuel. Remove it and shake it - if it rattles it's leaking.

If it's plastic it may be filled with fuel too. The foam they use has a tin coating of plastic or something on it to prevent the fuel from penetrating the foam. Trouble is that film dissolves with oil - even the natural oil on your fingers can dissolve it. Best to always use clean rubber gloves when touching the float. Except by weighing, you cannot tell if a plastic float has absorbed too much fuel and is too heavy.

Easy way - get another float - $5? - parts houses should have them.

But - you said you've lowered the float level. Did you also compensate for the drop? When you bend the float a little lower the float hangs lower in the bowl. It can touch the bottom of the bowl, where it gets stuck! Then fuel flows in unrestricted - out the vent, flooding all over.
Measure the depth of the bowl, then measure - and adjust the amount the float can drop - measure the float at the lowest point - make sure it cannot touch the bottom of the bowl. You want it close, but not to touch.

And - make sure the float cannot touch the sides of the bowl either.
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post #8 of (permalink) Old 04-14-2007, 12:35 AM Thread Starter
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It was the float, set it low once and then it worked fine for a couple hours of wheeling, caused problems when set it high and it's been fine since. She's alive and I've gotten some trail time in I'm happy. A new float is in order one of these days.
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