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A (brief!) history: This bike ran suprisingly well when first put back on the road 6mos. ago after at least ten years as a garage queen that was not registered but got started weekly and polished. The engine ran like new, no issues except for a quickly resolved idling problem. The bike had some gauzy white cotton-candy-like material stuffed in the stock airbox in place of the stock oiled-foam filter along with a couple of small blocks of very porous hard foam that seem to be there to provide a little restriction to the airflow as this white stuff is almost like running no filter. It and the blocks were dry, no oil whatsoever, and clean as a whistle. I left it alone and rode it. 3500 miles later the bike was still running great. I had done a few things like repair the charging system, tires, brakes, oil changes, camchain tensioner, but the motor was still running very well, smooth power from 3k to 8k, my self-imposed redline, without any "driveability" issues, misfiring, or flat spots in the power curve.
The problem started when I replaced that funky air filter with a stock pre-oiled foam filter. I ignorantly stuck it in there without removing the excess oil. The bike sounded strangled, didn't have the low to midrange torque it had before and misfired at 60-65mph (5500-6000rpm in 6th gear) at 1/3 to 2/3 throttle openings. I immediately put the old filter back in but the problem didn't go away. The plugs weren't fouled, tan in color, but I replaced them anyway. That did nothing. I tore the carbs partially down (bowls, floats, jets and diaphrams out but carbs not separated) and cleaned the jets and slides and adjusted the float levels to spec. They were way high, the floats were hitting the top of the bowl, indicating a rich condition (?), but there were no gas leaks. Jets are stock 115 and 17.5. Diaphrams were good, the pinholes in the jets were partially clogged but are clean now. Back together and there is much improvement but there is still a problem at 1/3 to 2/3 throttle openings and only at revs from 5k to 7k in any gear. I did not remove the needles from the slides, didn't have a pair of circlip pliers that would reach that far into the slides. The previous owner noted in the manual that he had removed the spacers under the needles. That would have gotten rid of the EPA-lean factory setting. He had also noted that he went to 117.5 main jets but must have gone back to stock 115's at some point. One other thing, when I changed the plugs I noticed that the spark was white and weak instead of blue and fat, but it has always been that way - the plugs were changed and spark was checked earlier when all was well - so even though that problem needs fixing, I don't think it's the source of this current problem. But what do I know?
I can cruise the bike around town keeping revs under 5k and roll the throttle on and off or hold it at any position and the motor just sounds happy and the low to mid-range torque is there. I can do a drag strip imitation and rev the bike out to 8k up through the gears and do 0-70mph in under 10 seconds (1st thu 4th gear). There's a slight misfire/hesitation at around 6-6.5k but I can rev right through it and power from 7k on up is strong like before. What I cannot do and want to do is cruise at a constant 60-75mph at half throttle. It doesn't misfire but power is on/off/on/off. If I twist it open past 2/3 power comes back on and I accelerate. If I roll off slowly the bike does the rocking horse on/off/on with the power thing that is getting my goat. If I close the throttle completely and quickly there's no surging, just normal engine braking. I can't go on any long trips with the bike like this, dadgummit. One other thing, now that the new air filter is drier than before it can be used in place of the funky white filter with little difference in performance. The white stuff makes the intake sound ballsier, the stock filter muffles it a little but performance is very close to the same.
So what do I do now? Tear down the carbs again? Separate them and dip them? I sprayed aerosol carb cleaner through the passageways and am reasonably sure all they are all clean and free-flowing. I don't have a carb balancing tool. The slides close at the same rate of speed when pushed up and released and you can hear the air escaping when they drop. The butterflies snap shut at exactly the same time, the clicks are in unison. I didn't think they needed messing with. I'm an "if it ain't broke..." guy whenever possible. I put homemade thin paper gaskets under the intake boot o-rings to help them seal better until replacements arrive. I don't think they are leaking, the bike runs too well at small and large throttle openings. Should I chase the ignition problem first. Could the coils be cutting out at those revs (5k-7k)? It doesn't seem like a misfire, more of a lean running or fuel starvation issue. The one thing I didn't check is the needles. How do you get that circlip out without a special tool? Would lifting them some more help?
The problem started when I replaced that funky air filter with a stock pre-oiled foam filter. I ignorantly stuck it in there without removing the excess oil. The bike sounded strangled, didn't have the low to midrange torque it had before and misfired at 60-65mph (5500-6000rpm in 6th gear) at 1/3 to 2/3 throttle openings. I immediately put the old filter back in but the problem didn't go away. The plugs weren't fouled, tan in color, but I replaced them anyway. That did nothing. I tore the carbs partially down (bowls, floats, jets and diaphrams out but carbs not separated) and cleaned the jets and slides and adjusted the float levels to spec. They were way high, the floats were hitting the top of the bowl, indicating a rich condition (?), but there were no gas leaks. Jets are stock 115 and 17.5. Diaphrams were good, the pinholes in the jets were partially clogged but are clean now. Back together and there is much improvement but there is still a problem at 1/3 to 2/3 throttle openings and only at revs from 5k to 7k in any gear. I did not remove the needles from the slides, didn't have a pair of circlip pliers that would reach that far into the slides. The previous owner noted in the manual that he had removed the spacers under the needles. That would have gotten rid of the EPA-lean factory setting. He had also noted that he went to 117.5 main jets but must have gone back to stock 115's at some point. One other thing, when I changed the plugs I noticed that the spark was white and weak instead of blue and fat, but it has always been that way - the plugs were changed and spark was checked earlier when all was well - so even though that problem needs fixing, I don't think it's the source of this current problem. But what do I know?
I can cruise the bike around town keeping revs under 5k and roll the throttle on and off or hold it at any position and the motor just sounds happy and the low to mid-range torque is there. I can do a drag strip imitation and rev the bike out to 8k up through the gears and do 0-70mph in under 10 seconds (1st thu 4th gear). There's a slight misfire/hesitation at around 6-6.5k but I can rev right through it and power from 7k on up is strong like before. What I cannot do and want to do is cruise at a constant 60-75mph at half throttle. It doesn't misfire but power is on/off/on/off. If I twist it open past 2/3 power comes back on and I accelerate. If I roll off slowly the bike does the rocking horse on/off/on with the power thing that is getting my goat. If I close the throttle completely and quickly there's no surging, just normal engine braking. I can't go on any long trips with the bike like this, dadgummit. One other thing, now that the new air filter is drier than before it can be used in place of the funky white filter with little difference in performance. The white stuff makes the intake sound ballsier, the stock filter muffles it a little but performance is very close to the same.So what do I do now? Tear down the carbs again? Separate them and dip them? I sprayed aerosol carb cleaner through the passageways and am reasonably sure all they are all clean and free-flowing. I don't have a carb balancing tool. The slides close at the same rate of speed when pushed up and released and you can hear the air escaping when they drop. The butterflies snap shut at exactly the same time, the clicks are in unison. I didn't think they needed messing with. I'm an "if it ain't broke..." guy whenever possible. I put homemade thin paper gaskets under the intake boot o-rings to help them seal better until replacements arrive. I don't think they are leaking, the bike runs too well at small and large throttle openings. Should I chase the ignition problem first. Could the coils be cutting out at those revs (5k-7k)? It doesn't seem like a misfire, more of a lean running or fuel starvation issue. The one thing I didn't check is the needles. How do you get that circlip out without a special tool? Would lifting them some more help?
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