Why is gas running right through my carb?

Anyone have an idea why when I turn on my gas petcock, the gas runs right through my carb? Draining out that little hose on the bottom of the bowl and onto my garage floor.

I took off my tank to check my valves but that should not have caused a problem. I did rinse off the under tank area before I removed the engine cap. And I did probably get water in the carb because I forgot to tape up the gas intake on the carb, but that was a week ago and I doubt there is any water in there.

I can't figure it out. Anyone?


Check the carb needle/seat (fuel valve) and float height. You probably have a little crud that has worked its way in between the needle and seat. Another possibility is the float is binding or hung up on something. In either case, this will result in this valve not closing all the way allowing the fuel to fill up the bowl and run out the vent hose. You might try tapping on the side of the float bowl to free the valve/float to get it to stop. Even it this works, you should pull the bowl and inspect everything.

Scotts right on the money....

Pull the carb, Clean everything out real good an you'll be fine. Most likely its junk in the carb.

Spend the extra $2.00 and put an inline filter between the petcock and the carb.

Bonzai :)


While winding the rest of this up, something occured to me. Water is enough heavier than gas that it will float the float higher than gas will. Before you do anything, turn off the gas at the petcock. Remove the 14mm bolt from the very bottom of the carb. Drain all gas (and water) from the carb. Replace the 14mm bolt. Turn gas back on and see if that fixed it. If not, go ahead with what I already wrote:

There are two needles in the carb. The one we usually refer to is the needle of the needle jet. It controls the jetting between 1/4 and 3/4 throttle.

The needle valve is similar to the valve that controls the height of your toilet tank. There is a float in the bowl of the carb that closes the needle valve when the gas level in the bowl is the correct height. The float raising pushes the needle valve into a seat to close off the fuel from the tank.

To clean it, it's easiest to remove the carb. At least you have to remove the bowl. To remove the carb (I have an 01 but have worked on a few 99 400's):

(1) remove the cover over the throttle pulley (where the throttle cables come in). Then loosen the locking 10mm nuts in the front of where the cables connect. Slide the throttle cables out of the bracket and pull the barrels of the cable ends out of the throttle pulley.

(2) Remove detritus, including the hot start tube, the TPS electrical connector (at the connector maybe 6 inches down the electric cable), and the fuel line.

(3) Loosen the phillips head screw on the air boot and pull the flexible boot back away from the carb.

(4) Loosen the 3mm allen bolt from the front of the intake manifold several (like 5 or 10) turns.

(5) Pull carb back from intake manifold and out into your lap.

(6) Pour gas from bowl into an environmentally safe recyclable benzene hazardous waste container or onto the floor by turning the carb upside down and onto its side until gas quits draining.

(7) There are four 3mm allen bolts that hold the bowl on the bottom of the carb. Remove these and lift bowl off of carb. 2 hold the idle adjustment screw and 2 hold vent tube guides. Remember which. Also, a rod, the accelerator pump actuator will flop over. Remember where it goes because it can slip out of the rubber flex boot and you will have to put it back in.

(8) Holding carb upside down, you are now looking at the float. Remove the hinge. On yours I believe there is a screw to hold it in place. Now lift float out. Attached to it, near the hinge, will be a inner metal tab with a hex ending in a cone. That's the needle valve.

(9) Remove it from float tab (gently) and make sure it is round and hasn't worn a notched ring in the cone part.

(10) Remove seat for needle valve. Blow both off.

(11) Reassemble, or clean rest of carb while you're in there.

Good luck,


Since you mentioned hosing it with the fuel line open, you most likely washed a little bit of dirt in.

Clean everything well, including the fuel line. you can check that the floats still float while you're in there, but I don't think that's the problem.

Originally posted by Mark Cantrell:

(6) Pour gas from bowl into an environmentally safe recyclable benzene hazardous waste container or onto the floor by turning the carb upside down and onto its side until gas quits draining.


Do it the first way for California, the second way for everywhere else.

Yeah, after I posted I realized the float was probably sticking. So I pulled the carb and cleaned it up. Put it back on and everything is fine. Thanks for the replys.

Mark, That was real nice of you to write that (long) reply. I know that takes alot of time to do that, nice job. :)


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