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Honda Motorcycle, CB900C needs expert advice? |
The Patient: 1980 Honda CB 900 C, stock except for Jardine 4 into 2 headers, being restored after 3 years abandoned in garage. 30,000 miles total. Condition and Treatment so far: Carbs replaced with overhauled unit by reliable shop, and synced to bike. (Original carbs were cleaned, but still popped as noted below; were never tested at high rpm.) Jets stock at 105, running in Houston Texas at sea level and 80 degrees F. Compression all excellent. Valve clearances all within specified tolerances. New plugs D9EA (recommended). Plug wires checked for 100% continuity. New battery: Alternator output 12 amps at 14.5volts, battery voltage at 12, coil voltage at 11.2, Pulsar gap to .016, static time checked Ok. Waiting on new timing light for dynamic timing. (Note: Pulsar was gapped with metalic gauge, although not magnetic.) She runs fine except: Problems: #1 When no accelerating (ie. loafing along, not much load on engine or backing down) get popping on right side Jardine, some times a lot of popping. Not full backfire, but a lot of popping. #2- Main problem: On opening her up, whether off the line, or on the highway, at 7500 rpm, power just quits. Will not go above 8000. Can sneak up on 8000 at less than full open throttle, but then same problem and will not go above 8200. Pulling on some choke makes no difference. Ran at 6500 for 2 minutes -- lots of popping on right side-- shut down and pulled 1 and 4 plugs immediately. Very light beige color, with a touch of pink(?). Absolutely no oil or soot or black. Possibly too lean due to Jardine headers??? Would that cause these symptoms? Diagnosis? Mechanics not familiar with Honda CV carbs, don't clean or thoroughly check them. The air cut-off valves and throttle slides aren't checked. The air cut-off valve plunger gets stuck in their bores due to old gas gumming them up. A basic carb clean will not clean them. And the diaphragms get torn/deteriorated from carb cleaner fluid. http://www.mrcycles.com/ # 11 Carburetor Com. Parts The slides - with the carbs assembled, lift 2 slides and release them at the same time. They should drop to the bottom of the bore at the same time. Check all 4. If they don't - Clogged slide lift holes. Worn out springs. Slide getting stuck in the carb top. Dirty throttle slide. Leaking gasket on the carb tops. Now let me ask this. When you put that header on did you rejet to the headers? otherwise pull the valve cover off and see if you have a flat spot on a cam or do a leak down test to see if your drawing air either from an intake or exhaust port. or perhaps one of your carb boots have a leak or crack, and I well assume you synced the carbs? You may have to readjust your main needle valves in your carbs since you opened up the exhaust with the headers. You may have to rejet as suggested but you can tell that by looking at the plugs. Do they look powdery white? If not your not too lean. Those bikes were not designed to run lean. Popping was very common upon messing with the exhaust. I would be more concerned about what sounds like fuel starvation at high rpm. Like I said try the needle valves. sounds like it is running lean up top end, try going up a size or two on the main jet, and check for exhaust leaks sounds like it is sucking air into the pipes some where. im guessing you changed the air cleaners? best bet would be to run the bike on a dyno and see what the exhaust emissions are doing. good luck. |
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