QuestionI have a 1969 CT90K1 that I start a couple of times a year, keep fairly fresh gas in it (with stabilizer in the gas), and drain the carb. I don't remember when I rode it last or what its performance was like when I did. I rode it for about 10 miles or more yesterday. It sputtered a bit when the throttle was wide open, but other than that, seem to run alright on flat ground. Anytime we would go up a hill in the road, it would struggle to get up the hill. I would have to downshift to first or second and my speed went from about 40 to 10 or 15 mph, with the throttle wide open. Even on flat ground, it seemed to be a little underpowered. I do have the high/low gear lever set to high. Sometime years ago, I had the cylinder bored and put in a new piston (maybe because I thought it was sluggish, but I don't remember for sure). I don't know if I ever checked the valves, but I think I did set the timing statically. I assume that I did all that correctly. I checked the spark plug and it is the correct one and is light tan and clean. Any advice on the power issue? Just wondering if these are normally a little sluggish and underpowered? Some other folks offered some ideas, so here is what I additionally told them: The filter is new, but I just pulled it off to be sure nothing had crawled in. It is clean and nothing plugging up the breather hole. The carb was new years ago and probably only has 100 miles on it. I did pull it and clean the jets before riding it. I'll check the points over the weekend and report back. I never checked the compression on the cylinder (or leak checked). Feels pretty tight when kicking it over, but more mushy than a crisp kick. Not sure if that is normal. Do you know? I have a friend that has a C70 and it feels sort of the same soft and mushy when you kickstart his. I figured I should be looking at timing, valve adjustments, etc. to see if everything is as it should be. I got the intake valve cover/plug off but the exhaust valve cover will not budge. I have tried wrenches, vice grips, heated with a torch numerous times, Kroil and PB Blaster numerous times, water pump pliers, hammers, etc. and it will not budge. It is pretty much rounded off now. Advice on getting that off and what I might consider for the power issue would be greatly appreciated.
AnswerScott, they aren't the most overpowered bikes on the planet, but a good CT90 should go about 60 mph.
Here's your checklist:
Check compression.. spec is 170 psi for an engine that is fresh and broken in properly. If significantly low, either the rings got stuck from sitting or the cam timing could be off a tooth. Cam timing errors will also show up as a difficulty getting the spark timing/point gap set properly.
Get that valve cover off... catch an edge with a big chisel, if you have to and verify that the valve clearances are .002" cold, on compression stroke.
Verify ignition timing at the F mark and also check the spark advancer to see if it is not stuck/frozen during engine operation.
Auto-clutch machines tend to seem a little soft when kicking the engines over. Be sure that the clutch adjustment is set correctly, otherwise the clutch can slip or jerk when shifting. The clutch disengages at idle and when shifting occurs, normally.
If carb is jetted for stock air filter, it should be okay. If you pulled the baffle out of the muffler or changed the air filter, then you may have to jet up the carb a step on the main jet.
Float level is 23.5mm for a K1 CT90.
Make sure that the gas cap is venting properly.
Bill Silver
