fuel leak

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gordonw
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Joined: Tue Oct 03, 2017 9:40 am

fuel leak

#1 Post by gordonw » Mon Oct 16, 2017 10:36 am

fuel leak from two carb overflows begins when engine switched off. Removed carbs and cleaned float valve seats, replaced and all seemed well, now doing it again, any ideas? cheers.

silverstrom
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Re: fuel leak

#2 Post by silverstrom » Mon Oct 16, 2017 12:51 pm

If the float needle tips are hard, pitted, or worn it will leak forever. Replacing the float valves (needle and seat) usually solves the problem.

The petcock should not be allowing fuel to flow when the engine is off and the petcock is in the ON position.

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phildu31
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Re: fuel leak

#3 Post by phildu31 » Mon Oct 16, 2017 5:27 pm

You have 2 problems at the same time.
First : your petcock is leaking.
Second : You have 2 carbs leaking.

For the petcock : dismantle it, it's easy, and check the internal rubbers.
Typical problem with the ethanol in bad quality/low price fuel.
Always use good quality fuel with no ethanol.

For the carbs, check float valves and fuel level.
For each carb, proceed like this : remove the carb tank, open the petcock by moving it to the PRI position and check that the float valve is ok by moving the float with the finger.
It should stop the fuel flow.
When this check is good, if carb still leaks you need to lower the fuel level in the tank.
Anyway, even you have no leak, you should check and adjust it.
Put a transparent hose ( diameter : 3 mm ) on the drain hose and open the drain screw. Your fuel level should be at 3,5 mm +/- 1 mm under the gasket level.
It is a test and try process by bending ( delicately ... ) the floats and be sure that the float doesn't touch the bottom of the tank, otherwise : no fuel !

Don't be in a hurry because this takes a lot of time.

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Speed Freak
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Re: fuel leak

#4 Post by Speed Freak » Tue Oct 17, 2017 4:38 am

Autosol metal polish + cotton swabs.

WARNING: The 2 posts which are holding the floater pin are very weak. Think twice how you get the force on the pin to get it out, otherwise you will break one of the posts.

Take the needles and seats out of the carb (check the condition of the O-ring around the needle seat) and polish the needle seat at the inside.
Do the same with the side faces of the needles where it gets in contact with the seat.
This will remove fuel residuals which hinder the needle from sliding - it`s not possible to remove them with solvents or ultrasonic cleaning.

Check the tip of the needles.
As long as they are not hard and brittle it should be fine.
Also check if the pin and spring in the rear of the needle are working fine.

Check if the floaters are not filled with fuel, they sometimes start to leak at the welding area of the 2 halves.
You do not really recognice it because the floater will still work - somehow... - when only one side is filled with fuel.

And finally check if your float bowls are mounted on the correct side.
Left and right side have different positions of the overflow pipe.
They have to be on the right side of the bowl (in driving direction), otherwise they start to leak earlier when the bike is on the side stand.
My bikes:
RD500 YPVS 1GE
RD350 YPVS 31K 1985
Honda CBR 1000 RR SC57
Yamaha R1 RN04

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