Keihin carb flooding badly

[AGilbert]

I have recently rebuilt my carb on my cobbled quad project and have run into a problem. The carb floods very badly. I got it to run for about 10 minutes after the rebuild but it ran poorly and then as it got warmer it didn't want to run at all. After some more investigating over the next couple attempts at getting it to run I came to the conclusion that the carb is flooding badly. When you turn the petcock on, just count to 5 and gas starts dribbling out the overflow tube. I checked the float height and it was at about 12mm which I thought was odd 'cause that should have caused the opposite problem. I persuaded it up to about 13.7mm and put it back together with no help resulting. I also check the float for leaks and that it actually does float. I then took the carb off and used a small metal tool that I made of the same size/shape as the float needle and made sure the seat wasn't buggered or otherwise misshapen which seemed to go well but when I put it back together it still just dribbles out the overflow tube. I have a wet spark plug, thin oil that smells like gas and the obvious fact that it just dribbles out on the ground anytime the tank is turned on but I just haven't been able to fix the issue.

Does anyone have any ideas about what to try next?

Are there any good replacement carbs for the Keihin PB20A?

[4x4van]

The needle valve/seat is not closing. That could be due to the float tab that presses on it being bent, or the seat is sticking open, or the needle/seat is damaged and won't seal, or there is some foreign object keeping it from closing. I'd start by making sure the float tab is not bent and actually presses the needle vale up into the seat. Remove the float bowl, press up on the floats while blowing into the fuel line inlet; the valve should close and stop the airflow. Next, remove the needle valve & seat from the carb and inspect it. In fact, if you aren't 100% positive that it is in good shape, replace it; they're cheap.

[muthey]

is your float the all plastic type, or is it plastic with a bendable metal tab to adjust height, I have an all plastic type that is non adjustable, and one of the little plastic arms is broke on it which allows for a constant flooding issue. Otherwise, are you sure you have it in right side up?

[AGilbert]

Mine is the all plastic kind; no metal tab. I am not sure it can go in upside down because then you wouldn't have the attach point for the needle to slid into. I checked the float really well when I had it out last for cracks and stuff and made sure that it did float and didn't let any air out when submerged. I am kind of confused because it ran rough before I redone the carb but it did run, now it just floods real bad and doesn't really want to do much of anything. I compared sizes on all the parts with calipers before I put the new kit parts in to make sure there weren't any parts swap problems and every thing was the same size. It should be a straight forward fix but nothing obvious has fixed it. I was thinking about the possibility that the seal around the inlet hole/passage might be leaking where the carb body/bowl may not be smooth/flat and gas could get straight into the bowl before the float had a chance to do it's job but that's about the only thing not obvious I can think of. Thanks for the help guys.

[muthey]

your plastic float can warp as well which can be your flooding issue as it is non adjustable, which is a pain. Easy solution is replace it or buy a whole replacement carb off ebay

[kb0nly]

The only way fuel can get into the bowl is through the float valve, so it has to be the float valve or the seat that it closes against. Did you pull the seat and replace it? I know guys will blow compressed air through all the passages of a carb when cleaning them and blow out parts they didn't realize.

What i would do, pull the carb, drain it, put a piece of fuel hose on the carb and blow into the hose while playing with the float and valve, move it up to what would be the closed position, are you still able to blow air through? If so then its leaking, pure and simple quick and easy test. Replace the float valve and seat, or just the seat if you already replaced the valve. Then test again. If you can hold the float up by hand and it seals then try again with fuel, you don't even have to mount it up, just sit the fuel tank on the edge of the workbench and hook up a length of fuel line to the carb and hold it over a bucket, thats how i test them before tossing back on the motor. If its still leaking then it must be the float is not pushing it up far enough, a new aftermarket float with an adjustable tab for the valve would fix it.

Leaking carbs suck, but they can also cause major engine damage from diluted oil and running too rich. There is a new replacement carb available to replace it on eBay for like $30, you can buy a new one for not much more then a rebuild kit these days. I still like to rebuild if the slide is not worn out, but sometimes a new carb is just the best option as they do wear out.