80 honda cm400 running problem

[belver1]

I have had this bike for about a year and half. It ran great until the motor let go. I rebuilt it and it runs ok except it will not run more than 60 mph wide open. When before it would do 75 or 80 before. I have tried gearing and it did not change it. Ive check the timing, went back to the orginal mufflers and air box, also have cleaned the carb and tank. Could someone please tell me what else i could try to make it run.
thank

[Johnj]

Hello and welcome to the forum. Make sure you have the valves set right and timed right. Good luck.

[belver1]

I have check the valves twice just to make sure, anything else would be grateful. I'm wondering could it have anything to do with the motor only having 700 miles on a rebuilt motor?

[Wrider]

It sounds like the cam timing to me as well. A lot of times even a tooth off could have drastic results like that.
If it's not that, I'd ask a few more questions. Does it rev as high as it used to? Does it take longer to get up to 60 than it used to? What happened when the motor let go and what all did you replace?

If it's not the timing, I'd check the clutch to make sure it's not slipping, I'd check the compression to make sure it's good, then I'd do a leak-down test to check the rings and valves.

[belver1]

I have 2 motors which ive had on this bike, the one that let go spun a rod bearing, the motor i rebuilt the ring just gave up and lost compression. I replaced the main bearings, rod bearings. and rings which fit within specs of a rebuild. Ive tried moving the timing chain one tooth foward and it did not change alot. the clutches feel like they are hooking up good it does not slip at all.

[belver1]

I check the compression, it was 120 on left side and 140 psi on right side, any suggestion?

[Wrider]

Sounds like they're both pretty decent. A little far off for normal, but decently high. All I can think of now is somewhere you didn't re-seal something properly. I keep coming back to valves and cams, but honestly without being there I'm out of ideas. Sorry. Maybe you can find a local board and get someone to come over and help?

[Johnj]

Try a little oil in the left side and see if that helps. That wouldn't keep you from going over 60 though. What I would do is re-time the valves. Make sure the sprocket index marks are flush with the head mating surface while the alternator "T" mark is aligned. Then make sure to set the intake valves at 0.10 mm or 0.004 inches and the exhaust valves at 0.14 mm or 0.006 inches.