Fuel leak into crankcase- again.

[r.e.wing_fc3s]

Pretty simple- the fuel leaks into the crankcase. Ive already had the carbs off and apart. The rubber ends of the needles are still flexible and show no signs of wear- slide easily in the seats. Seat/ o-rings ok. Floats adjusted and ran fine the last time it was out. Even if the float needle and seat or o ring were leaking shouldnt the extra fuel just drain out the correctly routed bowl breather hoses and onto the ground. I got one ride on the oil before i had to toss it out.

[T Legg]

What year bike do you have? If the carbs are gravity fed the fuel petcock should shut off the gas flow when the engine stops and no vacume is present. If it has a fuel pump no gas should flow when the pump is off. If the float valves are leaking bad enough to fill the crankcase while the engine is running I think you would see it dripping from the overflow tubes at idle.

[racerrad8]

The fuel will leak into the carb throats and into the engine before it gets to the overflow tee height. So, it will fill up the engine before leaking onto the floor.

You either have a leak at the o-ring around the needle seat or past the tip of needle; that's the only two ways for fuel to flow uncontrolled into the carbs.

Randy - RPM

[Greenlander]

Pretty simple- the fuel leaks into the crankcase. Ive already had the carbs off and apart. The rubber ends of the needles are still flexible and show no signs of wear- slide easily in the seats. Seat/ o-rings OK. Floats adjusted and ran fine the last time it was out. Even if the float needle and seat or o ring were leaking shouldn't the extra fuel just drain out the correctly routed bowl breather hoses and onto the ground. I got one ride on the oil before i had to toss it out.

Have you checked the petcock? I had a similar occurrence last year on my 84 FJ which is gravity fed. The leak turned out to come from the petcock which was the original. Replaced it with a new one from RPM (they safety wire it for you) and no leaks since. :good

[fj1289]

Pretty simple- the fuel leaks into the crankcase. Ive already had the carbs off and apart. The rubber ends of the needles are still flexible and show no signs of wear- slide easily in the seats. Seat/ o-rings OK. Floats adjusted and ran fine the last time it was out. Even if the float needle and seat or o ring were leaking shouldn't the extra fuel just drain out the correctly routed bowl breather hoses and onto the ground. I got one ride on the oil before i had to toss it out.

Have you checked the petcock? I had a similar occurrence last year on my 84 FJ which is gravity fed. The leak turned out to come from the petcock which was the original. Replaced it with a new one from RPM (they safety wire it for you) and no leaks since. :good

That simply means you had two issues - needle or needle seat issue AND a petcock issue.   

[r.e.wing_fc3s]

Thanks for replys. I have an 89 with electric pump so no petcock issues. Someone at the local moto shop suggested that using the side stand could be putting excess fuel into the #1 carb. He thought the float might be binding when tipped. Ill also recheck the seat o rings. And refit the center stand with a tight spring. 

[T Legg]

If your center stand spring was loose there is a good chance the holes the stand pivots on are elongated. I've had that problem leading to a low hanging center stand when up and loose spring.

[Pat Conlon]

Your fuel pump is leaking fuel...and....
1) your carb float needle seat leaks, or 2) needle seat o rings leak...or 3) both.

But it all starts with your 33 year old leaky fuel pump. When shut off, your fuel pump should not let *any* fuel pass by to the carbs. If it does, it's broken.

Fix your fuel pump or buy a new one, or install a 12v fuel shut off solenoid between the fuel pump and carbs.

Where's Noel? He will tell you his solution.

[r.e.wing_fc3s]

in an attempt to finally solve this problem i have replaced the needle seat orings and double checked the needle ends for softness and no ring from the seat. gently burnished the inside of the seats with a brass brush on a drill. all the floats were right on spec. checked each needle and seat for a good seal by blowing into the fuel tube. i also drilled a small hole in the choke vent circuit that was done by someone here on the forum.  i decided to take the fuel pump apart after hearing of this check valve function of the pump. My pump appears to be original with an oem connector and a mitsubishi logo on the bottom. powered off i can easily blow through the inlet and air comes out the outlet to the carbs. and vice versa. it was easy to bend the tabs and take the top off with the nipples in it. Upon inspection, theres alot going on in there. under the cap is the diaphragm -- which looked fine. then there are what look like one way valves for entry and exit of fuel into the diaphgm chamber. but outside the chamber it seems like the nipples share a common open area in the cap which allows flow form one nipple to the other?

[ZOA NOM]

Where's Noel? He will tell you his solution.

Understatement of the week. 

[Nimbus]

This has just happened to myself and I figured the needle valve/seat. Figured check this forum for confirmation. It makes a mess and having to flush the engine oil, at least twice. thanks for the answer.

The fuel will leak into the carb throats and into the engine before it gets to the overflow tee height. So, it will fill up the engine before leaking onto the floor.

You either have a leak at the o-ring around the needle seat or past the tip of needle; that's the only two ways for fuel to flow uncontrolled into the carbs.

Randy - RPM