Topic: 72 CB750 Engine knock/ overheating

[schwabbyboy]

Bike: 1972 Honda CB750 K2

This bike apparently hasn't touched asphalt for 15 years before I acquired it. Mostly garage stored. Wouldn't start at the guy's shop but would turn over. Brought it home and cleaned the carbs and the gas tank thoroughly. Started up first try and drove well. Ran a little rich but nothing crazy. I noticed a slight engine knocking/ tick and decided to do some research. Initially thought that the three bolts holding the flywheel in the crank case might be loose but it turns out that the older models of this bike don't have those bolts. Next I tried loosening the cam chain tensioner and the noise didn't stop but it did change. Seems to at least partially go away at higher RPM's. I am going to try tightening the tensioner this time and see if that helps, but wanted to get some advice first. Here's a video of the noise:

https://www.youtube.com/watch?v=1-bn...ature=youtu.be

Let me know what you think / possible solutions.

My 2nd problem is that the engine seems to be running hot or easily overheating. I don't know if it's a coincidence or not but I didn't notice anything until I started messing with the air mixture screws on the carbs to try and lean out the mixture. Rode it to work fine and then rode it to lunch, when I got back from lunch there was a little smoke coming from the engine slits on the left side of the top end. When it cooled down I noticed some oil residue on the slits where it was smoking, not a lot though. There was also smoke coming from the air release of the oil reservoir. A lot more seemed to be coming from the reservoir than the actual engine. Do I need a higher temp oil or is this a major engine issue? I should also note that the day this happened it was about 105 degrees out. Rode it this morning when it was only 90 degrees and some smoke still came out of the air release on the reservoir after a little ride around the neighborhood. Also smokes if it idles for a while, even in shade. It hasn't smoked or leaked any oil from the top end since that one time but I'm still worried. Please let me know what you think.

[evinrude7]

video is coming up as "does not exist".  do you use a fan when it's idling and parked?  i wonder if it's dust getting burnt off from the bike sitting.  my bike needed an oil change soon after the initial change when i acquired it. 

[BomberMann650]

It is an air cooled engine 

Your knock/tick could go away if you do a full 3kmi tune up.

[disco]

You are running fresh oil, not some 15 year sludge right?

Sounds like the 'pucks' in the head are leaking.

[calj737]

The point about letting it idle is very important; don't let it stand around idling for several minutes without a fan circulating over it, shade or no shade.

The "ticking" could easily be an exhaust leak, a tappet is loose (valves needing adjustment) poor oil pressure, etc. The full 3,000 Mile Service is mandatory for a fresh start up after a long winter's slumber.

The "knocking" could easily be the carbs are out of synch. And adjusting them to "lean" them out is contributing to a hotter engine. Best to do the 3K service, and fully clean the tank and carbs, set everything to stock (if the airbox and exhaust are stock) and give it a really good tune up.