Vacuum Leak Troubleshooting On Your Motorcycle

Vacuum leaks can be the cause of a poor running bike engine, including rough idle and difficult starting. In this video I'll explain the meaning of engine vacuum and discuss four methods of troubleshooting vacuum leaks on your carbureted or fuel injected motorcycle.

[@Gringo_In_Chile]

Good topic and thanks for explaining it so thoroughly. I have a 2015 Bonneville T-100 and would like to let everyone know that this is an issue on Older WC Bonnies'. You can see at 1:35 that the throttle body (TB) rubbers are angled. This design along with the weight of the x2 TB's will loosen over time and rough riding. Each TB has only two rubber connection points as well as being connected to each other. It is important to understand that the engine vibrates on its mounts according to engine speed, clutch action and chain torquing. This is different than the TB's that react more to frame moments. Anyway, my point is the protentional for vacuum leaks on this bike need to be checked at the start of each season.

[@stevewolf2620]

Excellent video! Recently my 09 started to idle terribly, and make a rattling sound in the left cylinder. Long story short, that rubber hose you show had fallen off! After putting it back on, I could still pull it off with gentle pressure. At almost 15 years old, it was time to change it. Project for today.........

[@stevewolf2620]

After a bit of investigation, I found that that hose goes to the charcoal canister that collects fuel fumes from the gas tank. A solenoid opens upon start-up to let the fumes there be burned. You may have heard of people doing "canisterectomies".
Bottom line is that if your hose ages and does not stay on while away from home like mine did, you can just put a vacuum cap on the barbed nozzle, and unplug the solenoid. The canister and solenoid are located under the front right tupperware.
This hose and canister are installed only on U.S. models, so it does not show up on all parts diagrams.
FYI, the hose has a bend and wider opening at the canister end, so it is BMW specific. You cannot just go to the auto parts store for some 1/4" hose. I put a vacuum spring clamp on the loose end at the throttle body.

[@tinderboxarts]

That charcoal canister is an emissions device which goes back at least to the early 1970s. They have never worked very well, and they have caused headaches for mechanics for decades. They work adequately out of the factory, but later they can become fuel logged, cracked or the vacuum hose can crack. Glad you found your problem.

[@hayrack8937]

Highly flammable sprays!

[@tinderboxarts]

Yes, they are. That's why I mentioned in the video that there is no need to saturate the bike with the stuff. A few squirts are enough to check for leaks.