Carb overflowed

[katt]

Uhm just finished rebuilding carb and it overflowed badly gas run out trough the roof over vent hole when i sucked on the vacuum line.

What could have caused this i put all parts in properly and i did not bend float in any way tried raising float by hand and plug closes fuel line tightly.

[gsx600racer]

If it didn't leak/overflow before you took it apart, and now it does after you took it apart, then there something you did or didn't do that's causing the problem.

[katt]

Its a carb from donor bike i haven't used it before, when i blow into the fuel input line when holding float by hand it does seal tight.

My theory because it was dry after carb cleaner and i started to put gasoline inside by forcing petcock open for 10 seconds, so it was filling it up and did not penetrate inside float hinge all the way so it jammed.

I should have let little bit gas inside then wait for it to lubricate everything and try opening petcock again instead of holding it open, could it be it?

Also there's copper insert where the plunger goes and maybe rubber gasket worn out i also seen few chopped spots in it. Too bad this frigging new gasket is not sold by itself dealer sell entire insert for almost $30 bucks!

[FrankenMech]

Typical bad needle valve assy.

[katt]

Valve is okay i suspect o-ring because it has tiny few tiny pocks.

I don't want to buy new kit from OEM it cost $30, all i need is 10cent o-ring, will check autozone.

As for new needle valve there's gy6 repair kit for $2.50 china or $5 in US can someone confirm the size of needle valve on QMB139 Keihin is as follows?

[KSR Moto]

I am not at home right now but I am pretty sure that it is the correct size needle for 139qmb carb

[katt]

Checked the old o-ring its all cracked (dry rot tire) on inside, also it sits bit loose in the carb body so i need new one.

Reason old carb did not leak is because i never removed needle valve copper housing on the old carb so old hardened o-ring was rotted tightly to carb aluminum body (can see its left overs after i removed it), now when inserted back it does not seal good anymore since ring is old and hardened. Mystery solved. 

Fond some info on o-ring material and chemical resistance.

www.martins-rubber.co.uk/blog/an-o-ring-material-selection-guide/

and more detailed here, you can type petrol or gasoline on the left to see what materials are safe.

www.marcorubber.com/o-ring-chemical-compatibility-chart.htm

[katt]

Ended up going to o'reilly auto parts and picking up National 010 o-ring for $1 says petroleum resistant on website, it does not overflow anymore.

[FrankenMech]

The O-ring is part of the needle valve assy.

The needle valve tip can also swell and crack when exposed to ethanol fuel unless it is made from the right material, usually 'viton'.

Valve seats and other seal surfaces corrode and pit when used with ethanol fuel. Moving parts like the fuel needle body also corrode.

Fuel can also enter the engine intake from a cracked petcock diaphragm.

O-rings take a 'set' and should not be re-used. Many less expensive types also swell and crack in ethanol fuel mixtures. The ethanol fuel mix used in the U.S. attacks many elastomers used for O-rings, gaskets, diaphragms, hoses, valves, seals, and other parts made for Asian scoots because ethanol fuel is not used there. Asians in general are far smarter than the majority of people here in the U.S.