Carbs over-fueling like crazy!

Hi All,

My first post and I already need help.

I bought a 97 from a buddy who moved back to Oz. He had an off and parked the bike for about 5 years.
Anyway, I ordered a few bits for the carbs, new manifold rubbers and stuff for brakes etc.
Eventually got as far as a start-up. Engine runs really sweet, but i noticed the pump wasn't working. Stripped and cleaned, tested and all seemed OK, so next move to reinstall and do a start-up again. Bike starts but then there is massive fuel leak onto the floor. At first I assumed float needles by-passing. Stripped and cleaned float bowls, reinstalled started up with pump disconnected. Runs fine. Reconnect pump and serious flooding out of what I assume is overflow/bypass pipe running out of the air vent manifold. Item 34 in the exploded view, Part No
TUBE,AIR VENT
product number: 16199MZ7640


So, any suggestions other than disconnect the pump?

Cheers

 

did you bench test the carbs before reinstallation?

If the fuel is coming out of the overflow, then the floats are not shutting off, so needles / floats is where I'd look.

I think there is a pump test in the manual - isn't it supposed to flow x mil a second ?

 

I did a search and seems not an uncommon issue, and as you point out bypassing needles have to be the problem. I did a bench test after the second clean and wrongly thought the pump was over pressure. All seemed OK with gravity feed. I'll do an individual float test and try nail which one is passing.

 

the one leaking won't be firing, so check exhaust pipe heat or look down carb throats (with air filter removed) to see fuel bubbling up under the slide needle.

there is zero fuel flow unless the pump is running so i don't see how u got engine running unless it was on some fuel remaining in float bowls.

 

Thx @squirrelman , at one stage I bypassed the pump direct to carb inlet. There was enough fuel for a gravity feed.
Thanks for the tip, I'll check with your method today.
What controls the pump pulse rate? Back pressure?

Steve

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right, back pressure.

 

I am totally remiss for not following up.
I cleaned the needle seats once again. Q tips eventually worked.
Bike started again with no leaks. A win at least, but there was still a miss. Turns out one sparkplug was dicky. Replaced all and bike runs well.
Now to replace the fork seals.
I live 40km from the closest tar road and it's the rainy season, so will be some time before I can get her down to the main road in March for a proper blast.


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Thanks for the update. Glad that you figured it out! Keep up the good work.

 

Thx bud. I have one gripe, and that's the fuel tap is buried under the tank and behind bodywork so can't be accessed to close fuel overnight. Strange indeed. So getting the carbs leakproof is essential.

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^^ really no need to shut off the tap as no fuel can flow through the pump unless it's powered up.