Hello all. I have a 98 m900 with 19,000 miles. No mods apart from after market exhaust and no carb vent boxes. Until recently when trying to start bike fuel would leak from the front cylinder head exhaust port. Now the fuel leaks when bike isn't running, all the fuel in the tank will drain through the carbs. Pulled the carbs off to find the right hand side carburettor inlet duct full to the top with fuel!! Float bowls all very clean and floats in good order. Would a faulty cut off valve be the cause, took off the unit, can these be tested, can blow through either end of the pipe and air passes through it. Could it be float height, how do you set these. Many thanks in advance all advice greatly appreciated. Clive from Ireland.
If the float and needle/seat assembly are sealing fuel will not enter the carb, but the reason why carbed bikes have a fuel fuel cut off device, either a manual petcock or vacuum cut offbecause shit happens, particularly in transit since the floats can bounce.. If memory serves me correctly, your bike came equipped with a vacuum cut off, which do fail. If so, replace it with a manual petcock. Then check the float assemblies , repair if needed, and confirm floats are set at 14mm.
Many thanks Howie yes the cut off valve is vacuum operated, if I replace with manual valve do I just blank the vacuum hose that attaches to the vacuum valve. Can I continue to use the vacuum fuel pump? I checked the float heights measured from the gasket base to highest part of the float one was 11mm the other was 12mm. Adjusted both to 14mm as you advised. Excuse my ignorance but does this mean the bowl will now hold more fuel or less. Thanks again for taking the time to read these
You're better off to blank the manifold, remove the fitting and hose, replace fitting with a short screw.
Bowls will now hold less fuel.
Prior to starting, drain what is likely to be upwards of 2 gallons of fuel/oil mix from your crankcase.
Replace the oil filter, filling it at least halfway with oil prior to install.
Fill engine with new oil.
Seconding howie...
I removed my vacuum petcock and replaced it with this: Motion Pro 12-0036 5/16" Inline Fuel Valve (http://www.amazon.com/Motion-Pro-12-0036-Inline-Valve/dp/B000WJA33I). There are cheaper options, but that valve has good reviews and I have not had a problem in 5 years.
The vacuum source for the petcock, I believe, comes from the intake runner on the bottom of the carb. You can seal this with a rubber cap - I would not replace it with a bolt because you can just pop off the cap when you want to synchronize your carbs.
Also, your floats may have been sticking open. But you just adjusted them so that would fix it. If you adjusted from 11 or 12 mm to 14 mm, then you have lowered the float height (since the measurement is taken from the bowl/carb body mounting surface to the bottom of the float) - it's confusing because you usually hold the carb upside down to take the measurement. The bowls are on the bottom of the carb when installed on the bike.
There is a picture about 3/4 of the way down this page which explains it better: Ducati Suite (http://www.ducatisuite.com/jetkit.html)
edit: I'm too slow :)
Thank you everyone for your advise. Put the carbs back together and noticed the internal overflow pipe in front cylinder carburettor was blocked hence why the fuel didn't exit here and flooded through to the engine. Have new cut off valve ordered will put carbs back on bike and report back thanks again
Good call on the overflow pipe. carburettor? Where do you reside?
Yes hopefully one of the culprits anyway Howie. I live in co. Limerick, Rep. of Ireland. [drink]
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I would also suggest using the search function and enter "carb flooding".
Cheers.
Just want to say a big thanks for the help and advise I received. New cut off valve fitted and carbs stripped and cleaned, float heights reset to 14mm. She fired and ran with no fuel leaks. Balanced the carbs and reset the idle. Went for a spin and she pulls nice and strong. Must recheck the plugs in the morning just to confirm the mixture is good. [drink]
You changed the oil and filter, yes?
I did indeed, flushed the engine with cheap oil then refilled with a quality brand.
Excellent.
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