Sticky BMW K75RT throttle grip

Q. I currently own a 1992 BMW K75RT. It has just failed its MoT on one single point. The throttle grip does not return to tickover when released. I have taken the handlebar mechanism apart and it is all working freely.

I have greased it with light grease. If I pull the inner cable out it goes back quite freely but when everything is connected up it will not return freely. I have oiled the inner and throttle mechanism without result. Before I take everything apart at the fuel end, which is a reasonably involved job.

Does anyone have any suggestions, please? Could it be a weak spring at the fuel end?
Leonard McNeill, email
 
A. If the bike has heated hand grips, check to see if it the rubber of the handgrip rubbing against the throttle/front brake mounting. If the bike does not have heated grips, check the hand grip is not against the handle bar end weight.

If it is an ex-Police K75RT then check it has not got a throttle damping screw in the above mentioned unit. (This was a form of fixed throttle to allow arm signals!).

You say that the inner cable is free and moves OK with the throttle cable disconnected, but check the routing of the cable. The fuel tank and other panels etc could have been removed and refitted and could be squashing the cable or it may be routed incorrectly.

While you’re doing that have a look at the throttle return spring on the throttle body bank. The cable comes down and goes around a quadrant by number two throttle port. There’s an outside chance there is a very large build up of dirt (courier bike) that could cause the throttle bank to stick.