PM999S
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- Joined
- Jun 26, 2019
- Messages
- 82
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While there are loads of threads on pilot/mixture settings, my problem doesn't seem to fit with the many very good suggestions. I recently installed new exhausts on my '72 Combat using baffleless peashooters. Initially, I jetted up to 280 from the 230s that were standard to compensate for the reduced back pressure and went for a quick test ride. The bike certainly revved up quicker although I was still unsure whether the jetting big enough albeit the plugs have never been cleaner. Partial closing of the throttle didn't markedly affect the acceleration so I thought things might still be a bit lean.
This is where things started to go wrong, because I decided to try out the 300 jets and change the aging filter with an unused K&N for the standard airbox from the 1970s that I found on eBay to see if it improved breathing even further. However, while the acceleration remained strong, closing the throttle set off coughing and spluttering to the point of popping and backfiring. So, I went back to the original settings complete with the old filter but the problem remained.
I then looked for air leaks and saw the previous owner had tried to repair the carb rubber hoses with a bike tyre repair kit. Certain that this was the issue, I fitted new hoses after carb-clean spraying the pilot/mixture channels and checking the seating of the floats. No discernable difference. Speeding up the idle and richening the mixture screws have helped a bit but not massively. I've also checked the seating of the new headers, secured by new brass roses and gaskets, and there is no movement there to let air in. What have I missed?
This is where things started to go wrong, because I decided to try out the 300 jets and change the aging filter with an unused K&N for the standard airbox from the 1970s that I found on eBay to see if it improved breathing even further. However, while the acceleration remained strong, closing the throttle set off coughing and spluttering to the point of popping and backfiring. So, I went back to the original settings complete with the old filter but the problem remained.
I then looked for air leaks and saw the previous owner had tried to repair the carb rubber hoses with a bike tyre repair kit. Certain that this was the issue, I fitted new hoses after carb-clean spraying the pilot/mixture channels and checking the seating of the floats. No discernable difference. Speeding up the idle and richening the mixture screws have helped a bit but not massively. I've also checked the seating of the new headers, secured by new brass roses and gaskets, and there is no movement there to let air in. What have I missed?