Bonneville America Forums Forums Technical Forums General Tech Gas tank vent problem

I took a trip trhough the Hill Country today and everything was fine for about 175 miles. Then when I got on the freeway where I was in danger or being run over by double trailer rigs, I could not go over 3500 RPM and there were some very large grades. Gearing down made it worse-the further you twisted the throttle, the less response. Started and idled just fine-limited to about 3500 in each gear.

I was sure the high speed jets were clogged. Then I stopped and filled up with gas and the problem cleared up. Then it dawned on me about breaking the vacuum lock by opening the gas tank cap. I drove 90 miles back home at any speed I wanted and had no problem.

It did not rain and I did not run through any water. Anyone know what causes this beside riding through water?

you said it yourself,the tank vent. could have gotten plugged or maybe the tip over valve got stuck, or if you had the tank off maybe it got pinched in the front by the rubber tank mount.

Thanks Ian. The tank has never been off the bike. I got a big clean up job ahead becuase I rode through %$^& fresh tar that I could not avoid so I guess I will just examine everything when I am under there.

I was mainly wondering what preventive measures to take to prevent this in the future.

If you cut the bottom of the vent tube at an angle it is much less likely to clog.

If it was a clogged breather hose, you should have heard a quite audible "whooosh" when you opened the gas cap.
Beyond that, make it a practice to check the 4 hoses every time you lube the chain, or every time you change your oil.
2 are breathers - engine and fuel tank, and the other 2 are airbox drains. Those 2 should have "squirrel condoms" inside them to keep from drawing dirty air in beyond the filter. They need milked and cleaned once in awhile also, although that's not related to the problem you had...

You could install a vented fuel cap like Brent sells. I have never had any problems with mine.

Thanks for all the good info and suggestions. This board is the best.

The cap from Brent is a HD cap that is available from many other places for less money. I posted a list of the HD bikes it fits a while back.

If you get it from someone other than Brent, make sure it is the same one. It's made by Kuryakyn and they make a number of models some vented and some not. Maybe Dog's post has the part number listed. It would take some digging to find my paperwork/packaging.

No part number but I did say what tank it has to be for. The right side fat bob is vented while the left isn't so on the kick stand it doesn't leak. So you want the one for the right tank not the left and with right handed threads since they make left handed threaded ones too.

Fits 83 and later XL,FXR,Dyna,Softail,& Roadking.

Mine is a Kuryakyn "Flush Mounted Vented Gas Cap 8309" there has been some problems with some of the newer bikes with the thread being compatible??

yes I think late 06 and 07s had a problem with not wanting to thread in if I remember correctly.