Will a .132" non windowed seat overpower a float causing an overfill in the fuel bowl? If so, is there a remedy short of buying an new needle valve and seat?

The carb is a 2040205 on a 1970 LS5. The fuel pump is a stock type unit, but I cannot say whether it had ever been replaced by a previous owner. If it was, that was more than six years ago. The float is set to .375, per Lars suggestion. When I remove the carb top the float is covered with fuel but it still measures at .375 so it does not appear to be fuel logged.

With the top off I removed the fuel from the bowl and the placed a piece of wood over the float fulcrum and lightly clamped down on the fulcrum to hold it in place. I then cranked the engine and the bowl filled and the float stopped the flow as expected. I observed the action of the float during both the emptying and fill stages and its motion was uninhibited by the metering rods and the power piston tower.

In a separate test, I had an assistant crank the engine while I held the needle valve in the closed position to check the seal between the seat an it's mating surface in the bowl. No leaks were observed.

After reassembling the carb and starting the engine, the fuel bowl over filled.

The new seat is the only thing left that I can think of.

Thanks for your replies.

 

It sounds to me like your float IS fuel logged and I would recommend replacing it before replacing anything else.

 

A .132 seat seems a little large if the engine is stock. I think stock size would have been .107-.110 or something.

Regardless, I'd replace the float first, or at least take it out and test it beside a known good one. I'm tempted to think it's the float.

 

This the second float I have tried. The first one was about 4 years old and the current one is an old one as well. I tried letting the current one float in fuel for about 30 minutes before I Installed it. It did not sink. Is that a good way to test a float?

I ordered a new one and will try again.

Thanks for your replies.

 

If the seat has been drilled to a larger size, there may be a bur that is allowing a leak. Your assistants finger pressure may be enough to stop the leak, but the float can't. Siphon the gas out of the bowl, gently hold the needle down and put a few drops of fuel into the seat chamber. See if it leaks out. But is does sound like your float is bad.

 

The seat was purchased new. I did do a static test prior to cranking the engine and the seat held the fuel for about 20 minutes.

I did weigh both floats after removing them from the bowl and the both weighed 7 grams. My impression was that the nitrophyl floats acted as a sponge and retained the fuel therefore increasing it's weight. Does the float absorb fuel on it's surface while in the bowl and the return to it's normal weight as the fuel evaporates?

Thanks for your reply

 

Are you using a stock-style needle with the little clip that attaches to the float arm? If so, that little clip should just be hanging from the edge of the arm facing the float, not in one of the two little holes in the arm - it's a common mistake to put the clip in one of those holes. This can cause flooding problems on occasion. It's a quick check and you've probably already ruled this out - but just in case you haven't I thought I would mention it.

 

I did weigh both floats after removing them from the bowl and the both weighed 7 grams. My impression was that the nitrophyl floats acted as a sponge and retained the fuel therefore increasing it's weight. Does the float absorb fuel on it's surface while in the bowl and the return to it's normal weight as the fuel evaporates?

To answer this specific question - no, the float has a coating on it that prevents it from absorbing fuel. As the float ages, this coating breaks down and the float can then start to absorb fuel, resulting in a "heavy" float.

7 grams is about right for an early Quadrajet float though, I think. The 1975+ ones were I think about 6 grams.

Still, if both of the floats you have used are old, I would start by putting a new one in there and be really picky about getting the level measurement right.

 

Thanks for the explanation it certainly accounts for what I have experienced so far. What is a typical lifespan for a float used in a street application?

I have been very picky about both the clip and the float level measurements.

I get to do it one more time tomorrow.

Thanks again.

 

I can't say what an average lifespan would be for a float, it likely varies considerably. A brand new one with a surface imperfection for instance could absorb fuel very quickly, and an old one could hold up for a long time under the right conditions. It's just usually a good idea to replace the float whenever a carburetor is rebuilt. An exception to that might be the brass floats, but I don't have any experience with those and don't use them.

Good luck and let us know how you made out.

 

The initial results are in and the new float appears to have fixed the flooding problem. i was then left with my original nemesis, the dreaded main nozzle drip.

I have the curb timing set at 8*. With a few adjustment of the curb idle speed and the mixture screws the drip has ceased. I have the mixture screw set at four turns from being lightly seated, but I have not yet finished the factory set up. I

am being cautious about declaring victory because it has behaved itself in the past only to start flooding and or dripping at cold start the next morning.

Thanks for all of your suggestions, they proved very helpful.