QuestionI recently purchased a 1985 Yamaha fj 1100. It had been sitting for a couple of years and did not run. I emptied the fuel, cleaned carbs and completed all normal maintenance. The bike fired and ran. well. But, the bike is very hard to start when the engine is cold. It also Sputters at full throttle. do you think the carbs need to be synchronized or would a total rebuild be in order. Thanks.
AnswerLee, I suspect that you didn't get all of the old fuel solids out of the system before you fired it up, so some residues could have come down through the petcock, fuel lines and behind the float valves and wound up in the float bowl and gotten sucked back up into the metering passages/jets.
Hard to start cold problems are generally related to blocked idle passages. Sputtering at full throttle could be either main jet issues and/or the emulsion tubes that mix fuel air in the main jet holders or the air bleed passages in the carb throats. If the carbs have rubber diaphragms, have a close look at those as well. Any vacuum operated controls could be ruptured, as well. This will cause vacuum leaks that will lean out the metering circuits in one or more carbs.
The carbs are interconnected with fuel lines/passages that all need a thorough cleaning, so I think that the carb rack needs a good cleaning, along with the petcock.
http://www.bikebandit.com/houseofmotorcycles/1985-yamaha-motorcycle-fj1100n/o/m7... Looks like it might have a vacuum diaphragm on the petcock, which can fail and cause restricted fuel flow to the carbs.
Beyond that I would check over the spark plug caps for equal resistance values around 5K ohms. Fresh spark plugs would be a given in this circumstance, as well.
Bill Silver
aka MrHonda
