valve assembly under float area?

valve assembly under float area?


Mena, AR
1976 CJ5 258. MC2150 carb, PSC steering, Team Rush upgrade, 1 piece rear axles, all electronics relayed. Coming soon: Herculined tub, camo paint- and a bunch of filthy, muddy kids!
76' AMC 258 i6 / 4.2l CJ5 with MC 2150 or 2100

Guys, what is the valve assembly on the underside of the float area called? I think its the problem to my venturis leaking after engine shut down.

Also, is it interchangeable in either a 2100 or 2150 like the carb kits are?

Since I'm here, how can you tell the difference between a 2100 and 2150?

Its a brass "button" like valve on the very bottom of the float chamber- not the float valve.
Its not the jets. Damn I wish I could pull better images with this phone. Wish I could post pics.
Ok Thank you. Does this come with a rebuild kit? I think I got shorted.

Also, I believe its the reason why gas keeps coming out of my venturis (only 1 at a time) after shut off.

Is this common on an m/c?
Ok thx. If its faulty would it allow fuel to bypass after shut off? Is it sold with a kit or separate?
Ok I really appreciate it.
The power valve allows an extra shot of fuel to enter the venturies when vaccum drops for a second going from the idle jets to the main jets when you hit the gas. It's purpose is to keep your engine from leaning out and stumbling when you first hit the throttle. They tend to blow out if you have a bad backfire, and they do go bad from age after a few years. All MC2100 and 2150 carbs have them, and they're the same exact part that Holley carbs take. It should have come with your kit, but if it didn't, you can pick one up at O'Reilly's for only a few bucks in the Holley section. They come with different weight springs to determine at how much vaccum they'll open, so you'll want to get a good, unported vaccum reading to get the exact right one. I believe the kits usually come with a size 45, so you can just get that one if you want to be in the ball park on a stock AMC 258 i6 / 4.2l .

I also read that Motorcraft carbs tend to leak a little fuel around the power valve threads causing them to run rich. This can easily be fixed with a little permatex thread sealer to seal the power valve to the main body. I did this to mine when I rebuilt it.

As for your current issue of fuel dripping from the venturis when the engine is shut off, a bad power valve won't cause that because it's under the fuel bowl and actually lower than the main jets. TRUST ME ON THIS!

The only thing that could cause what your describing is that the fuel level in your float bowl is raising higher than the level of venturis either because your needle and seats are leaking slowly, your float level is set too high, or you have seriously high fuel pressure still in the line after shutoff that's pushing past an otherwise good needle and seat. Since you're running a stock mechanical fuel pump, I'd really be surprised if it's a fuel pressure issue.

Replace the needle and seat, and set the float level 1/2" or 9/16" between the top of the carb body to the top of the float at the opposite end from the needle. The float level setting for your specific carb will be listed in the directions that came with your kit.

Good Luck!
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