81 CB750F project

[81cb750]

I just picked up an 81 CB750F as a project for my son and I to work on. When we picked it up, it turned over but didn't run. I pulled the carbs off and cleaned them up. Had to replace all the screws holding it together (what a mess). Anyway, it has 46k on the odometer and once I got it to fire, the engine was pretty noisey. I was happy about the fact that it actually ran pretty smooth.

This is my first CB750 so my question is, are these motors normally pretty loude? I am not referring to the exhaust sound, there was a lot of lifter noise and I am worried about a possible rod knock! I did not have it running very long due to loosing battery power. The bike is mostly coplete with only a few body parts missing like the side covers and rear shield for the headlight assymbly. Any thoughts as I decide wether or not to do a total rebuild on the motor?

Any input, advise or insight about this bike is very welcome! Thanks.

[WICHOL98]

i just got a 79 cb750 and i got it running this weekend and i noticed the rod knock noise it kinda faded but one of my pistons is not firing

[MightyMutt]

I may have some parts you can use. I have the left side cover, the whole headlight houseing(including the lamp, both front and rear turn signals, both fenders, and Seat, Tank, and several other parts. Email me maybe we can work something out.

[FLYTYM]

The noise isnt normal,these motors are pretty quite.The lifters might need to be adjusted or possibly something internal is bad.

[theban]

I have just picked up a cb750F 1981. It runs well, and after I put a a plug in the open vacuum nipple on #2 Carb its running smoother too!

but there is a clanking/knocking sound at low RPMS.
http://www.youtube.com/watch?v=YVPpScwzbfM 

this is what it sounds like! something like yours? I hope its due to carbs out of synch, since thats the quickest fix!:)

any input?

[Re-run]

Probably easier to do a new thread on this one, the topic was 4 years old!

ANyways, I would do 3 things, adjust cam chains with engine at idle, check valves, adjust carb sync.
Try pulling in the clutch and see if the noise gets lower. If it does, then a carb sync will probably be your ticket.