Whats With My Gas Cap

Wheel Rush

New Member
Jun 21, 2008
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Last week I got the engine installed and have it up and running, (Kings 80cc), what's with my gas cap ?

It seems that pressure evaporation is escaping and leaving a wet gas ring around the cap on the surface of the tank,
what to do about it ?

Also, I have noticed a eyedropper full of what seems to be oil, below the carb. on top of the clutch gear housing, not sure where it is coming from, . . it looks a little heavy, (oil), to be gas ? Anyone know what it may be, I cleaned it off yesterday, took it for a ride, when I got back there was nothing there, so I thought it might be evaporated gas, leaving oil behind, then this morning it was there again.
 
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Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
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up north now
Don't worry about the oil is more than likely just some oil left from a drip of your gas/oil mix that the gas evaporated out of.

Now about that cap....most are problematic. Here's a couple of "helps".
Drill a tiny hole in the top of the cap. This helps pressure escape instead of it building up and leaking around the gasket. The tank should be vented anyhow, but a lot of them seem to have a problem there.
Don't fill it all the way up.
 

Wheel Rush

New Member
Jun 21, 2008
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BikeGuy 31,

The gas cap has an extended cylinder in its center, I am taking it that you are saying to drill a, "tiny hole", just into the surface of the cap, if I do this the cylinder that holds the pressurization spring, will not be effected correct ?

Do you have any idea why the pressurization cylinder assembly does not work well enough to prevent this evaporation in the first place ?

My guess, . . is that there is not enogh pressure on the rubber washer that seals it when it is turned tight ?
 

misteright1_99

New Member
Mar 21, 2008
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Treasure Coast, Florida
If you look at he gas cap, the gas goes up inside the cylinder, thru the tabs that lock the cap to the tank. I made another rubber gasket and added it to the stock one, and drilled the hole as Joe said, and have alot less leaking then before. If you just add the gasket without the hole you might have too tight a seal and the gas wont flow out the petcock...
 

Dave31

Moderator
Staff member
Mar 1, 2008
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BGJ, wasn't it you who posted pic's on drilling a hole in the gas cap? I can't find it, I know it's here somewhere...
 

tinkerfinger

New Member
Jun 10, 2008
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If the cap is like my Boygofast cap. you dont have to drill the vent on top. Place cap on table upside down., peel up rubber seal as far as you can. untill it is touching the spring loaded tabs. You will see that you can drill a small hole just outside the border of where the rubber seal seats. This will allow it to vent via the 4 small holes on bottom of cap. But regardless. Do not fill it up all the way if you know your not going that far. Its still moving, bouncing, vibrating, leaning and sloshing around like a good fun motorbicycle should.