CL72 high rpm issueWent through the carbs - again, but more thoroughly with Davo's help. Cleaned out the jets, replaced the slow jets with stock ones, removed the screens on the fuel line banjos, removed damaged o-rings on the carbs and carb insulators and replaced, checked float condition and hight, made sure all the vent holes were open, put the carbs back on and fired it up. The left side started to backfire almost immediately. I removed the left carb and re-checked everything then put the slow jets that were in it when I got it back, put it back on and found the backfire was still there. It improved a bit if I turned the mixture screw all the way in, but I won't ride it much like that... Rode it around and it still (regularly) sputtered at high rpms.
It would be so great if it was the gas cap. Any quick and easy way to test that without taking it apart or replacing it? Suggestions? I'm thinking of swapping all the jets from one side to the other to see I can eliminate some possibilities. My goal is to not have my sons signing in to this forum in 15 years to try and figure out how to get dads old motorbike running since he never could... Hi,
When I get a bike with these kind of problems and I'm not sure what it causes, I take a stroboscope (after a view basic tests like leak down test and compression) , connect it to a battery (not the battery of the bike), and place the pick-up device first at the left high tension cable. Start the (already warm bike) and rev it up while I point the strobo at the flywheel. If the flickering of the strobo is constant and like it should, I do the right side. This way you not only checking the dynamic advance timing, but also if the spark is there. The flickering must be constant, and not irregular. It both sides are smooth, you are sure the ignition system is ok and the voltage is high enough to trigger the pick up of the strobe. Now you can focus to the carbs or other related issue's, just make sure you don't look back and start to doubt which often initiate a yo-yo effect in your head. In general: In most cases people are not sure where to look, the only way out is experience or using the an analytical scientific approach, or a mix of both. There is not one motorbike related problem which cannot be solved this way. Actually, the more complex the problem, the more interesting it gets. Very complex problems are fun to solve, because these problems take your analyzing scientific approach to another level, challenging your capacity's as a human being. I often draw a flow chart of things I have to check, it helps, and make sure you don't run into circles every time or chasing your own tail. Reading in also helps, yesterday we where at a swimming pool, kids where playing and I was solving a problem of my CB400F and an electric problem of my SS50.
assembly of Japanese motorcycles requires great peace of mind (Pirsig)
DONZI - it's not the gas cap. I unscrewed it while I was riding at full throttle and found no improvement. Glad to be able to cross that off my list though.
Jensey - I absolutely agree with everything you said. I'm looking forward to the satisfaction of figuring out what was the problem. I also spent a day relaxing, as you suggested, however, my children are 2 and 5 years old so "relaxing" means chasing them around and saying, "NO" a lot. Most of my reflective thinking happens at the end of the day after a glass of wine and a bedtime story (one for me, the other for my sons). We are superior to machines (for now) and I won't give up. Cheers, Graham  Belvedere by candy_gr@m, on Flickr PROBLEM SOLVEDWith the help of DAVO, we found that one of the carbs had a clogged passage way (the one in the the red box in this image)
 Screen Shot 2013-07-19 at 6.59.24 PM by candy_gr@m, on Flickr Once we cleaned it out and put everything back together, it ran as it should - it went from being a big, heavy moped to being a motorcycle again. A huge thanks to Davo and to everyone on this forum for helping. See you on the road!  1964 Honda CL72 Scrambler 250 by candy_gr@m, on Flickr Hi,
I wrote earlier : An ultrasonic device cleans all the passages in carbs, also passages which are not accessible. Actually, when doing an engine, I do it anyway, as a standard procedure / precaution, it's only 10 to 15 USD each time (if you don't have a cleaner yourself). The same for cranks, and if applicable for cam shafts (when they have oil passages) and oil pumps. Actually all parts with inaccessible oil passages. If you're also doing fours you learn these things quickly. btw, beautiful bike. Here in the Netherlands there are no CL72/77 (just a few imported bikes). Jensen assembly of Japanese motorcycles requires great peace of mind (Pirsig)
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