Choke knob trim

This is something you can try if you are running rich or have poor mileage and you can’t seem to solve the problem no matter what you do. It isn’t meant to take the place of a proper float level, correct jetting, and a well sealed system. This will not solve problems caused by running the wrong grade of gas or lugging the motor. It is simply meant to be an additional tool. It has been done on enough bikes to make me believe that everyone should just go ahead and do it.

During discussions about poor mileage and the smell of a rich running motor  two things were discovered. The first is that when we take the choke cable out of the bracket to work on our carbs we could be pulling on the cable too hard causing the sheath to be pulled slightly out of the crimp on terminators on either end of the cable. You will see a scuff mark on the sheath by the terminators if it has slipped. The second was that a cable that has not been touched may still have the knob bottom out against the stop too soon. If either of these are the case with your bike the choke will not go all the way off even with the knob all the way against the stop. I wanted to see if either of these could be the problem with my bike. My bike smelled of rich exhaust at shut down or when setting at a light. I didn’t want to buy a new cable unless I knew this was the problem so the mission was to find a way to work with the cable I had. I couldn’t do anything on the carb end so my only other choice was the knob end. I found out the choke knob is just hard rubber and cuts very easily with a razor blade. I began by cutting approximately 1/16 inch back from the butt end of the knob (Not the stop) running the blade all the way around.

Basically cutting a washer shaped piece off the end.

After cutting that piece off the knob it was still going in tight against the stop so more trimming seemed to be in order because I wanted to know my choke was really all the way off. The rest of the slices were much thinner. I would cut a slice and push in the choke. I did this until the knob stopped going in but there was a small gap (About the thickness of a business card) between the knob and the stop. (See note 1)

With a gap between the knob and the stop I know the plunger is seated completely in the carb. It does not affect how far out the knob will go so you still have full choke if you need it and the midpoint clicks are all still there too. The knob is still firmly attached to the bar so it doesn't appear trimming the knob has weakened it. That is really all there is to it. I put a piece of white paper behind the cable so it would show up better in the pics. All the work was done with the carb on the bike and the cable connected to the carb. All I did was take the cable out of the bracket.

The results are my bike no longer smells rich. It reacts much better to choke adjustments. And the overall running, especially the idle, is much better. I have picked up about 4 mpg also.

Note 1. The round rubber stop is adjustable by turning it in or out. It is used to set the tension on the cable. Turning it clockwise will increase the tension on the cable and move the stop in. Turning it either way will affect how soon the knob hits the stop. So have it set to where you like it before you begin the trim.

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DISCLAIMER: This information and procedure is provided as a courtesy and is for informational purposes only.  Neither the publishers nor the authors accept any responsibility for the accuracy, applicability, or suitability of this procedure.  You assume all risks associated with the use of this information.  NEITHER THE PUBLISHERs NOR THE AUTHORs SHALL IN ANY EVENT BE LIABLE FOR ANY DIRECT, INDIRECT, PUNITIVE, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, OF ANY NATURE ARISING OUT OF OR IN ANY WAY CONNECTED WITH THE USE OR MISUSE OF THIS INFORMATION OR LACK OF INFORMATION.  Any type of modification or service work on your motorcycle should always be performed by a professional mechanic. If performed incorrectly, this procedure may endanger the safety of you and others on your motorcycle and possibly invalidate your manufacturer’s warranty.

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