tank question and oil question, probably pretty basic

these could be stupid questions, but ill ask them anyway...

is it possible to have a vacuum leak through a bad gas cap?(is anyone looking to sell a tank?)

hypothetically speaking, IF i over filled my bike with oil could it get up into the cylinders and foul the plugs?

thanks much!

 

Your gas cap has a vent in it (or should have) so that the tank does not create a vacuum.

If you overfill your oil it will most likely get pushed out into the air box (seen this happen). If you are getting oil in your cylinders it could be the valve seals are going bad.

 

Another common scenario is that the carb floats aren't at the right height, or the float needles aren't sealing well, and the petcock is not shutting off correctly (it's vacuum actuated), and the result is gasoline overflowing the carburetors and flooding the crankcase.

After that, you have a lot more oil volume, and, of course, it's a lot thinner as well, so, between gas that may have gone down the cylinders and thin oil that can easily get past the rings, things get fouled.

 

thanks!

The reason i ask is because i rebuilt the carbs and changed the head gasket this winter, went to start it up and it was acting crazy. hanging idle, bouncing around, id give it throttle and it would die, sometimes id give it choke and it would die, sometimes 3 and/or 4 cylinder wouldn't even fire.
Valves were all in spec, compression test was good, float levels were all good. Ordered all new parts and o-rings for the carbs. Figured it was something to do with the fuel being old
Put in new plugs and hooked up the alternate fuel source and she ran great, almost hooked the fuel source up to my helmet and went for a ride!

Regardless my tank is shot. Anyone have an extra they're willing to sell?

 

Is it the TANK or just the original vacuum-op petcock?

And it would really help if we knew what bike you're talking about.

 

the petcock was replaced last year, don't think it could be that right?

its an xj700 86'.

 

Replaced with?

What do you think is wrong with the tank?

You could have a petcock issue or a plugged gas cap vent.

Unless there's something physically wrong with the tank itself (severely rusted internally, somebody "lined" it and did it wrong, etc.,) then it's probably not the culprit.

 

Yeah, bet it's the petcock. Rebuild it or replace it. Pretty damn cheap option to try first. Make sure you use an inline filter, too.

 

thanks guys

The lining was peeling off in the tank, i tried my best to remove as much as i could see of the lining with Por15. I then re lined it with the Por15 kit.

Im going to go through the petcock and gas cap, refill her with fresh fuel and then try it again. Ill get back to you guys soon, thanks Much!