Gas Cap Problems

floridaboy

floridaboy

Member
I have two bikes one has a Grubee engine and the other has a Dax engine. The gas cap on the Grubee vents like it should but the cap from the Dax engine does not vent right. When i look at the two i can not see any difference betwen the two. Has anyone had a venting problem and fixed it or found out what is the cause of the cap not venting? I know that i could just buy a new one but i like to know why some thing does not work.
 
When i was useing the Dax cap when the engine tryed to die i could open up the cap and it would start running like it should. If i put the Grubee cap on it would run with no problems. Both bikes run with no problems with the Grubee cap. If i put the Dax cap on eather bike i have the problem of the engines dying after a short distance.
 
Oh o.k. that explains that. I wasn't sure if you knew for sure if it was the cap not venting. You definitly have that figured out. I don't know what would cause that? I have had a lot of trouble with those cheesy caps the way the spring is in there but no venting problems.

John
 
It took me awile to find the problem but i still would like to know how the caps are vented and what makes the one not vent. I guss i could get another one and hope it is good and then take this one apart to see what makes it tick or not tick in this case. I thought i would ask incase someone has allready taken one apart and knows how they work.
 
I thought about that and was wanting to know if anyone had tryed it. Don't know if it will leak gas back on the tank. That would not be to good i would think.
 
I found out if you turn the cap up side down and raise up the rubber gasket and look around the edge you will find the little vent hole. The cap that i had used a small slit not a hole like the the cap that worked good. I took a small bit and lined up with the slit on the outside edge of the cap and drilled through the edge and into the slit and made it larger. Problem solved and no hole in the top of cap that water can get in. Ypu only see the small hole ion the edge of cap.
 
I've got the same problem with a DAX Titan. I can hear the cap venting when the bike is sitting but it vapor locks or something when riding. It stalls and won't start until the cap is loosened and tightened. I was told it's flooding but it's the opposite, it's starving. It'll idle up sometimes before dying, that's lean, not flooding. I haven't figured out how to remedy it yet.
 
All these vented caps will leak if you fill the tank up to the top!!!
I always just fill my tanks a little past 3/4...
Drill a tiny hole and go ride!!!
dnutdnutdnutdnut
 
I am starting to build custom gas tanks and I have been looking at making the caps myself as the vented ones available are either too expensive or not worth the material used to make them. If anyone has any suggestions for vented gas cap designs that are leak proof I would love to hear it.
 
I had the same prob with one of my gas caps. Don't drill a hile in the top of the cap.

Bend the gasket out of the way and drill a 1/16 or smaller hole in the metal there and it's fixed
 
same problem on zoombicycle 80cc had to drill small hole top center of gas cap and even into the guts to vent rite....it worked
 
A low pressure check (one way) valve would allow air to enter the cap, but not allow fuel to leak. The carb should be able to hold back what little pressure builds in the tank from sloshing. I've seen such valves in 1/8" npt male. Some are even adjustable.
 
Does anyone know how to stop the rattle from the gas cap?

Most of my bike noise comes from the rattle of the cap. I can put my hand on it and it stops. I was thinking of putting a dent in the top of the cap to make it stop.

Would silicon help stop the rattle if placed on the under side?
 
The proper way to fix this according to my friends dad who designs parts for Boeing.

Note where the cap stops turning. Mark the high spot on the cap if there is one. Or the spot most forward on the cap.

Remove cap. Remove "O" ring. Place a very strong magnet on the cap directly next to where you have decided to drill your relief port to catch most or all of the shavings.

Using a drill bit the same or slightly larger than the stock hole drill a hole in the same area as the original vent in relation to your target area. Slide magnet over the hole to remove the debris. (He also suggests dropping a strong neodymium into the tank or epoxying one externally to catch any and all polorizable metal or sediment. Which according to mr B is 85% of all debris found in any given fuel pod.)

Next make note of where the rubber gasket lays in accordance to the vent ports so as not to hinder their function. Any overlay can be trimmed away with a toenail clipper or using the elipes of a hole punch used for punching holes in papper. (He uses the hole punch for cutting out holes in gaskets also. Thanks Mr B!)

Replace o ring on cap and run. It wont hurt to have to much venting but it will for there to be to little.

If you find one hole isnt enough try another. Loosening the gas cap will tell you its enough when it no longer effects the way it runs.

If the one way spill valve is stuck closed or primary in conjunction with the vent hole it could be a material defect keeping it from functioning properly. Replace cap.
 
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