Working on a '72 CB450 and it is putting up a pretty good fight. Sorry, this might be a rambling post -
When it came to me I cleaned the carbs (completely apart - CLEAN), put some fresh oil in it, did a quick check of the timing (static) and started it up. It started, ran, and actually sounded pretty smooth. I only did a compression check when I initially got the bike, but I typically try and get them running and check again once some oil has circulated as it always seems to go up. I forgot.
In the meantime, the bike, other than the motor, got a cosmetic work over. It has, new coils, wiring harness, and condensor. New combo reg/rec and battery. Charging correctly at just a tick over 14 volts when running. It has a very high hanging idle no matter what you do. You have to hold the throttle open to keep it running. I've gone through and checked the valve clearance first at .05mm. Same effect. I thought it might be the carbs so I went through them again. Now, the main jet and pilot jet were aftermarket, so I found an old set of carbs with original Honda/Keihin brass and used them. Same results. Even cleaned and tried the second set of carbs. Still hanging idle.
Yesterday, after rechecking the valve clearance, I tried starting it again. I got some crazy popping/back firing out of the left cylinder. Pipe would go warm then hot then warm.
I have verified the fuel level in both sets of carbs using the clear tube method. I am confident that the carbs are not the problem. Then did a compression check with a slightly warm engine.
145psi on the right and only 35 psi on the right. BOOOOOOO!!! Will do a leak down test tonight to see if I can pinpoint where the leak is. Somehow I think I have a sticky exhaust valve on the left. I wish I had one of those cute little cameras that I could put in the bore to take a look.
So, today I will check the valves and timing AGAIN. Are there any marks that I can see on the cam etc (while it's still in the frame) to verify that things are put together correctly without taking the head off? I'm assuming that since it actually ran, that it is put together correctly. It could be that the rings are still sticky or a valve is sticky. I have ran the motor for about 15 minutes total - a few minutes at a time, with a big fan on it. And, I've actually ridden the thing about 1-2 miles. It sure seemed like it pulled pretty good. I took and old cover and put a hole in it so I can check the timing with a timing light without getting oil all over the place.
Any other ideas? I'm gonna be sad if I have to take this clean clean motor out of this freshly painted frame and go through it. I'm going to put some seafoam in the oil and see if that can loosen thing up ?
