Autolite 4100 sticking float?

[Kerry j]

I have a rebuilt 4100 1.12 on my 69 Bronco with a stroked 347 and it usually runs great. But there have been a few times when the front float sticks and makes the carb spew gas out the breather that's on top of the front of the carb. I've taken it apart 3 or 4 times and can't see why it's hanging up, it seems to be free and clear, but it still hangs up once in awhile.

Any ideas or suggestions? I would really like to keep the carb on this outfit, but it's starting to worry me because it puts so much gas on top of the engine when it sticks that I'm afraid of a fire. If I can't solve it, I'll have to look at getting some other carb; maybe a 670 truck avenger.

Thanks for your help...

[jayb]

Are you pretty sure its a sticking float?  I've had gas come spitting out of the vent the carb due to the fuel boiling in the carb.  Fuel these days boils at a very low temperature, around 170F according to the tests I did on my car several years ago.  The problem I had was that I'd shut the car off for a few minutes and it would heat soak, and then when the fuel in the line to the carb hit the float chamber it would boil, because it was heated up during the heat soak and was no longer under pressure once it hit the float chamber.  Gas would come gushing out of the vent on the Holley 750 for a few seconds when this happened.  A return style fuel pressure regulator solved this problem.

If it is a sticking float, have you deburred the float hinge components to make sure there is no issue there?  If the carb is clean and there aren't any burrs or dirt/varnish buildup in the float hinge components, there isn't any reason the float should be sticking.

[Kerry j]

It's not just boiling out a little fuel, it put about 1/2 cup of fuel on top of the engine; I had to sop up all the fuel that collected in the intake manifold areas that would hold fuel because they were all full of gas. Kinda scary...

This carb, was rebuilt by Pony Carbs; which by the way, I wouldn't recommend to anyone. The charged me about three times what it should have cost. In any case, they were supposed to set the carb up for off road application since it was going in my 69 Bronco. Evidently what they did was install a spacer or block in the fuel bowel so the bowel can only hold about half as much fuel as it normally would. The piece they put in has glue smeared all over it and sometimes the float was hitting this spacer, so it couldn't shut off the fuel feed.

I took the spacer out and filed in down so that the float clears it now and that seems to have solved the problem... I hope. I'll drive it and see what happenes.

[Garyford]

Kerry,

 Many years ago I had a 4100 carb, brand new float,  sink  (at least I think that's what happened), and spewed fuel out the vent, ignited and burned the car down.

Sounds like that is not your problem but something to consider. 

[Kerry j]

When I smelled and saw all that fuel on the engine, that's exactly what I was worried about. I've got a huge amount of time and $$$$ in that Bronco and I sure don't want to see it burn up. I think I have it fixed, but I'll be watching it like a hawk to make sure.

[FirstEliminator]

    A friend came by my shop the othe day talking about his Holley overflowing the bowl. I asked if he had a good fuel filter and such. He said yes. He installed one of those dual feed lines with the fuel pressure gauge and determined it was around 12 or so. Somebody told him to mke sure he has a vented gas cap. He found his cap was not vented. He put a vented gas cap on and the pressure hasn't gone that high since and has cleared up his problem.

   Mark