my sons 50 leaks gas from the cap when he gets on bumpy ground. The caps is screwed on very tight but seems to spill out onto the tank top. Is there a rubber casket that's missing or something? Thanks

 

I'm not that familiar with the 50's but my Falcon 250 does have a rubber gasket inside the gas cap. If it is there you may want to check and make sure the top of the fill hole/cap area isn't scratched or gouged. If there is a scratch or gouge in the sealing area that the gasket isn't sealing it will allow the gas to come out. Also look for any deformation of the cap or cap sealing areas where gas can come out. If you want to pinpoint the area that the gas is leaking out of you can mix up some dish soap and water and brush/douse the tank top (with the cap installed), close the petcock and blow throught the vent tube. You should be able to see bubbles coming out from the area the gas is leaking from. If there are no gouges and the gasket is in place the cap or the tank may not be threaded enough or cross threaded (threaded crooked). One last thing you can try is covering/coloring over the gasket in the cap with a grease pencil or crayon. Screw the cap on fairly tight and then take it back off. You'll be able to see the color transfer from the gasket to the tank and the sealing area on the gasket. If there is color left on the cap gasket the colored area is most likely your leaking area. If there is an area on the tank that has no color that is most likely your leaking area. It's not foolproof but it usually works. Hope this helps.

i8amm

 

Yes there is a rubber gasket in the cap but that might not be your problem:

What happens is if you screw the gas cap down to tight you actually seperate the gas tank around the threads..I had this happen so I ordered another gas tank..within a month same problem. I then went to the hardware store and got some gasket sealer that is "gas" safe/resistant and on the inside of the gas tank at the top where you screw on the cap I smeared it all around it. I waited a day and did a second coat. Hasn't leaked since. This is obviously a problem with these from the factory.