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Date: Thu, 28 Sep 1995 12:27:11 -0400
From: Rob Lentini

Ed Guzman is asking how to fix K backfiring:

Here’s an [edited – wd] earlier post, friend…

Rob Lentini
’87 K75S
Tucson, AZ
K Whiner MC#11
———————– [Original [edited – wd] Message] ———————-

Major backfiring is NOT acceptable, though some is inherent. Have your dealer check the fuel/air ratio at idle, throttle body synchronization, and the throttle switch adjustment. You may also have too little throttle cable “play” which may be holding the butterflies slightly off idle, keeping the throttle switch actuated. Check for a audible “click” at the injector area as you slowly ease off the twistgrip to idle. If the switch is incorrectly adjusted or the throttle cable too tight, you won’t hear the “click”, and the engine will receive fuel as you decelerate, causing backfiring.

Rob Lentini
87 K75S
Tucson, AZ

Date: Thu, 26 Oct 1995 20:11:20 -0400

In a message dated 95-10-26 06:49:33 EDT, Jim Olin writes:

>Also, it backfires when I let up on the throttle. Is this an indication of a
>serious problem?

The problem is almost certainly a mis-adjusted throttle cut-off switch – located on the rearmost end of the throttle plate shaft assembly – left side of engine, just ahead of the coils. This switch is supposed to close – with a faint click – just as the throttle closes completely. This signals the ECU to cut the fuel flow to the injectors if RPM is over 2000. If it is mis-adjusted so it doesn’t close (and click), then the injectors keep pumping in fuel even on throttle off conditions. This will cause the backfire. The switch is adjustable by loosening two screws and slightly rotating the entire switch assembly. Set this correctly and most of the K bike backfiring will go away.

And BTW, use the Clymer manual with confidence. There are very few (if any) significant changes between a ’89 and ’90 K75.

Paul aka Dr. Sprocket

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