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Fuel leak into crankcase- again.

Started by r.e.wing_fc3s, February 03, 2021, 08:32:42 PM

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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.
T Legg

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
Randy - RPM

Greenlander

Quote from: r.e.wing_fc3s on February 03, 2021, 08:32:42 PM
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
Keep the rubber side down
1975 Harley 250 (Cagiva ) fun but unreliable. Sold After 6 M
1975 Honda CB 550 fun and reliable,sold
1980 Suzuki GS 850 daily driver,weekends.Very dependable. Sold for the FJ in 89
1984 FJ 150K of year round (fun)commute in SoCal

fj1289

Quote from: Greenlander on February 06, 2021, 11:35:06 AM
Quote from: r.e.wing_fc3s on February 03, 2021, 08:32:42 PM
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.
T Legg

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.
1) Free Owners Manual download: https://tinyurl.com/fmsz7hk9
2) Don't store your FJ with E10 fuel https://tinyurl.com/3cjrfct5
3) Replace your old stock rubber brake lines.
4) Important items for the '84-87 FJ's:
Safety wire: https://tinyurl.com/99zp8ufh
Fuel line: https://tinyurl.com/bdff9bf3

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

Quote from: Pat Conlon on February 08, 2021, 10:27:02 PM
Where's Noel? He will tell you his solution.

Understatement of the week.  :Facepalm:
Rick

Current:
2010 Honda VFR1200 DCT (Full Auto!)
1993 FJ/GSXR 1200 (-ABS)
1987 Porsche 911 Carrera (Race)
1988 Porsche Carrera (Street)
Previous:
1993 FJ1200 (FIREBALL)
1993 FJ1200ABS (RIP my collar bone)
1986 FZ750
1984 FJ600
1982 Seca

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. :yes: thanks for the answer.
Quote from: racerrad8 on February 05, 2021, 08:04:24 PM
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
92 FJ1200
1953 Nimbus
1988 Honda VFR 400R
2018 Montesa 4rt
2003 Suzuki SV650S
1968 Honda CL450
1976 Honda CB400F