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I got my Bonneville tuned to the point it was starting on a half kick a while back. It was cleaning and adjusting everything. I also raised the needle a notch.

Then I changed silencers to a straight through 60's style muffler and took off the side covers and stock air cleaners in favor of pods. Now it's back to the start in 40 kicks or less. Plus when going down the road it cuts out when I'm at a constant rpm and spitting back through the carbs like when I first bought it.


I'm reasoning that I maybe opened up the airflow to the point I screwed up the carb settings. Spark, compression all fine. Plugs are a beautiful light brown color so maybe leaness is not the problem.

I've heard these MK ll's are finicky. Would bigger jets help or hurt...or do nothing?
 

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Hi rmak,

I guess from the carbs you are running that your bike is a 140. Sorry I don't know much about them, however I know that the 69 bonnie had 190 main jets and the 71 (with different pipes and filters) had 180 mains, so if you up your mains by 010 you should be close, I'm sure someone out there will know for sure.

Webby
 

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Yes, thanks Webby. I've been asking so many questions here lately about my new bike I just assumed everybody knew. It's the 78 T140E. I'm really just trying to find out if anyone put larger jets in their MKll carbs when changing silencers and air filters.
 

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Hi rmak,

I've changed my filters & pipes to the pre OIL type, so I fitted 190s I guess it should be pretty close. As my engine's still in bits I've no idea how it runs but someone out there will know for sure.

You could do a plug chop to check, but it sounds like it's running lean.

Webby
 

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Then I changed silencers to a straight through 60's style muffler and took off the side covers and stock air cleaners in favor of pods.
I have a '79 T140D with the sixties-style mufflers and modified air filters. When I made those changes in the early 80's, I also installed a carb rejetting kit from an outfit called Burak By-Products. This is the jetting setup from that kit: throttle slide 3.5, throttle needle 2A1, needle position 2 of 5 (counting from the top), pilot jet 15, pilot air jet removed, needle jet .106, main jet no change (200) cold start jet no change (25). I run N-3C plugs. The bike was transformed and has run well since.

Maybe this will be some help, I dunno. With the plugs looking so good, I have to wonder if the problem is with your carbs, but I figured maybe this setup information would at least add to your base of knowledge.
 
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