2bbl Rochester Carburetor Adjustment Questions

[DeppvomDienst]

I just rebuilt the 2bbl rochester carburetor on my '74 Chevy 350 since it was leaking fuel. I figured that the ethanol was causing this problem. I cleaned it out and rebuilt it and the leak is still there with the added problem that every time I clutch, the engine quits.

 

I initially did adjust the float according to specs (19/32" and then 1+ 9/32" float drop) with the first measurement being from the air horn gasket to the brass float seam and the float drop being measured from air horn gasket to the bottom of the float. This was what my Chilton's said to do. All this added up to maybe 1/4" total movement which seems wrong to me. I test drove it and the carb still leaked and the engine quit whenever I clutched to coast the truck. So I took it apart and put more float drop in the second time by measuring the float drop measurement from the same spot (float seam) as for the first (9/32") measurement. All that effort got me the same results of leaking and the truck quitting every time I clutch while letting it coast. Can't find a vacuum leak so far and the truck as the old bulletproof mechanical fuel pump that was installed when Nixon was still in the White House so I don't think fuel pressure is a problem.

 

Any ideas? Thanks in advance.

[Squirrely]

All I could really find for a manual trans was a float adjustment of 7/32", not the 19/32" you set. And that was for a 75....

 

Only other common thing I kept reading was that the 2bbl is particularly sensitive to rebuild kits. Lots of problems with different gasket thicknesses, check ball getting stuck, floats going bad, etc.

 

 

 

I'm probably not much help right now. It's late and I've been in LA for 2 months.

[txab]

Any carb kit I ever purchased contained documents that covered all the specs for the carbs the kit was designed for. Where is it leaking from?

[Duelin]

This is from a 1974 Chevrolet passenger car and light duty truck overhaul manual.

 

 

The manual says for Float level adjustment with air horn inverted measure the distance from lip at toe of float to air horn gasket. Now for the float drop let he float hang free. and measure the distance from lip at toe to the air horn gasket (not bottom). And the measurements are19/32" for float level and 1 19/32" for drop. which looks like 1" difference. The Manual list three carbs for manual transmissions, 7044111, 7044113, 7044115 and three for automatic transmissions 7044112, 7044114, 7044116.

 

Also you have different measuring spot depending on the float design. That being said there isn't a hole in the float letting gas in and causing it to be heavy? Also if it is leaking all the time check you oil level and make sure the oil isn't contaminated with gas.

[Doug_Scott]

Without know where the carb is leaking fuel, there is not much anyone can help you with. A general rule of thumb for safe float level is to hold the top half of the carb upside down, and set the float so it is parallel with the edge of the carb. Float drop is not critical, just make sure it does not drop far enough to touch bottom of float bowl. As long as the needle comes competely off the seat and the float does not contact the bottom of the bowl, it will work.

Really need to know where the fuel is leaking from though. You may want to check your fuel pressure as well. Should not be more than about 7psi, and should really be closer to 4 psi. If it is too high, it will push the needle off the seat. Also check the float itself (as mentioned in earlier posts) for leakage. If it is the brass type float, shake it, it should not have fluid inside. If it is one of those black plastic types, check the weight, it should feel very light, almost no weight at all. Toss it in a bucket of water and see if it sinks, or, just buy a new float if you are not absolutely sure about it.

Have you considered an exchange carb?