K Bike Tech

Throttle Body Air Leaks

Introduction:

As K bikes age the rubber boots between the throttle bodies and the cylinder head can crack due to age and heat cycling. When this occurs it allows air leaks and the bike may run poorly.

K75 or K100 TB Boots:

Under the throttle bodies - behind the fuel rail in this picture.

K100RS4V, K1, or K1100 TB Boots:

Symptoms:

Rough idle

Difficulty in syncing throttle bodies

Diagnosis:

GAS: With the bike idling, spray some UNLIT butane gas or propane gas around each of the throttle body boots using a handheld torch. If the RPMs increase from the gas leaking in then you have a leak and the throttle body boots need to be replaced.

It's probably a good idea to do this outside. I've never had the propane gas flame up when doing this but it doesn't hurt to be safe and you probably don't want propane floating around in your garage.

Replacing the boots:

Click here to see an example of replacing K75/K100 throttle body boots.