Buick 455 Stage 1 carburetor floats from top

Hi everyone, I have a weird problem on my 455 stage 1 engine, my Rochester Quadrajet carburetor floats from the top, after some minutes running the top gasket between body and air horn becomes wet and fuel will going down everywhere and engine revs up etc. and this problem will not shown on only one carburetor. I have my original one, I have another 68 Pontiac Quadrajet, a 1976 modified one, even I tested an 80`s Quadrajet, I rebuild all of them before installing, double check everything, even for test on one of them I bend float lower then original place that it barely have a little movement to close the needle, I double check the float needle and the float needle seat to body, the float itself is OK. the accelerator pumps are new and OK, I checked jets and needles. my carb filter is original with anti drain valve, my mechanical fuel pump is original non stage 1 AC fuel pump, my return pipe is in place, on the carburetor all vacuum ports and PCV valve and canister are also attached.

After two weeks working on them and testing I have not any clue that what is happening and why it is floating.

It will be very helpful if anyone have an Idea that what is going on.

 

I would be willing to bet the return line going back to the tank is obstructed.

To test, simply remove that line from the pump, and put a long piece of hose on the fuel pump return, put the other end in a gas can. If you see no gas in the return line to the gas can then replace the pump, the fault is internal.

Your pushing fuel past the needle and seat assembly, and when that is happening on multiple carbs, then we look at the fuel pressure. Put a gauge in line between the pump and carb if you have one.. I suspect it will read 12-15 psi.

Good luck
JW

 

New pump time!

 

1. Have you vacuum-tested the needle and seat? Is the gasket between the seat and the casting still in place? IS THIS A HIGH-FLOW SEAT using a larger-than-stock fluid passage?

2. Has the float absorbed fuel (become heavy?)

3. Are the carburetor castings still reasonably flat? VERY common for Q-Jet castings to be high in the middle, crushed-down at the two front bolt-holes. A straightedge across the gasket surface of the air horn and main body will tell that tale. There are folks selling a "straightening" service--and at least years ago a person could buy the fixtures to perform the straightening themselves (fixtures were unreasonably expensive.)

4. As has already been mentioned...verify your fuel pressure. Enough pressure will blow the needle off the seat even if everything else is perfect. Note that Q-jet carbs were produced in many versions over about twenty model years. Not all the floats are the same--and some are designed (along with the carb body) so that they cope with high fuel pressure very poorly.

 

Could the float pivot be too "closed", such that the air horn doesnt hold it down? The needle can be lifted by fuel pressure in that case, causing overfilling.

 

I ran into that one a few years ago for the first time in 35+ years of working on Qjets.

 

I like to run a regulator even with mechanical pump mainly to stabilize the fuel pressure. Cuts down on the pulsation and allows the needle to do it's job better. I've seen it wildly pulsating from 6-9 psi. Regulate down to 5 and runs alot better IMO

 

My fuel pump is new NOS AC fuel pump. I will test it, maybe it is not compatible with today`s fuels? also will check the return pipe.

I have not equipment to vacuum test the needles but I tested it normally and it works, Only thing that seems abnormal is fuel pressure.

I always check those pivots and will bend it close to where air horn seats. but I don`t know if the float itself be bend lower than it should be it can cause a problem?

 

I haven`t test the fuel return yet but another question cross my mind,

Is it possible that when I bend the float lower than it should be it make opposite effect?

 

No, a too-low float setting alone will not cause a fuel bowl to overfill.

 

As Ken G states the c shaped clip that the float pivots on can sometimes become pinched which allows the float to move as the bowl fills which allows the needle to move upward and allowing more fuel into the bowl. I have seen this many times.
I always spread the c shaped clip so that the top of it protrudes above the top of the main body which allows the airhorn to hold the clip and the float positively in place.
Also when checking the float level always hold down on the clip when pivoting the float to check the full level.

 

Finally today I found time to test the return line, It was OK, I use 8 BAR air compressor from engine side and clean it trow the tank and it was OK, I also tested fuel pump`s return outlet. It was clean and OK.

Also I tear apart the carburetor and double check everything, C shaped float clip, float seat to carburetor body, float height (according to user manual 13/32) air horn was OK, I checked contact marks on air horn gasket to see if in somewhere it is weak but it was OK, what I saw without pressure on table (carburetor was full of fuel on the table when I worked on it), when I fix the air horn on it place and tighten the screws and set the accelerator pump arm. upper gasket becomes wet. in fact it floats on the table!

Is it possible that the NOS gasket that I use on my carburetors is not compatible with today`s fuels?
Is it possible that fuel comes up from acceleration pump pipes non stop?
Fuel pump have any pressure regulator on it? is it possible that fuel pump`s pressure goes higher than it should be?

 

Some old carburetor mechanic told me that if your gasket between the fuel pump and engine block be thinner that it should be, it can cause higher fuel pressure but it dosen`t seems right on Buick fuel pump because it`s rocker arm is straight. On some European cars I saw such things but on Buick I don`t know.

 

So it is leaking while on the bench top unpressurized and static?

 

It is because I don`t have the needed equipment right now but I vacuum tested the needle and it is OK. even mark on viton end of the needle shows that it seats and tries to seal.

It is not leaking from those plugs under the carburetor, when it was on the bench full of fuel and I put the air horn on and tightened the screws and put the accelerator pump arm it start to leak from air horn gasket, In fact air horn gasket itself will absorb fuel and leak it out and it is original GM gasket from GM rebuild kit.

 

Th

Thanks Larry, I will test the pressure but another reason that I`m not going to test the pressure is that the engine can`t run with that amount of fuel in intake.

 

I'm missing something. If it is leaking removed from the vehicle is the fuel pressure a moot point?

 

I guess there is multiple problems. When it is on the car fuel pressure push the needle and carburetor floats, second problem is when it floats from the air horn gasket it goes to other passages for example to the by pass and directly to intake or goes from the bowl to ventury than to the intake.

I don`t know how air horn gasket should resist against fuel but I think it should keep fuel on the bowl.