Topic: CB750f 1975 Supersport tank gas vent

[roll58]

Hi everyone,
Where is located the vent on this tank cap... I can't see no hole anywhere. After a 30 minutes ride if I open the cap there's a big whoosh of air and I had a few stall while riding... the bike start to struggle like "out of gas" and stop and I had to wait a few minutes to start again.  I read that no venting in the cap may have caused the stalling.

[ekpent]

 Under that metal ring is part of the vent system.

[jlh3rd]

you got my curiosity up, so....i looked at my 550f's cap. see your last pic with that raised ridge on it? and directly underneath, on your third pic, you see a small protruding part of that inner cap part?
I wonder if that is it...a needle does go all the way into that.....

[roll58]

Yes you are right, I think it's block, I tried with pressure air with no success, I think I will make a little hole in the top of the cap, will it cause some problems?

[DaveBarbier]

I would remove the seal and try and soak with penetrating oil before I drill holes. Maybe even a rust remover like Metal Rescue or the equivalent.

[roll58]

I would remove the seal and try and soak with penetrating oil before I drill holes. Maybe even a rust remover like Metal Rescue or the equivalent.

It's ok now, I managed to unblock it, I test ride for 2 hours and everything is fine. thanks.

[Don R]

 It's like a check valve, it doesn't vent pressure, it vents vacuum. On occasion you remove the cap and it'll go woosh. If it's pressure, it will do that. If it's vacuum then there is a problem.