Just bought a CB750 kz '80

[Vignobles]

My project for the next months, a 36 year old CB 750 kz and this is new for me, because untill now I only had sohc 750's. The motor is about 98% compleet and the sparparts are in boxes. The parts as the seat bumper and the flashlight mounting I found on the internet.
The engine isn't running because it has been standing for a few years and the carbs need to be cleaned.
I'm very exited to get started....

 

[Flogger]

Welcome... check the compression first...

 

[Steve P]

Hi - I've just restored a KZ, great bike. I did a full strip of the engine so if you need any advice let me know.

 

[Vignobles]

Thanks for youre advice, when I have questions I'll ask on this forum.

 

[amc49]

Compression check and for sure run the valves. Besides carbs clogged from sitting then not done valve work is the single biggest cause of trouble on them. The OEM spec too close and leads to some of that trouble, look for no closer than .005" on valves. They burn at the allowable .002" and can on .003" in some cases. Most of the time even the dealers did not set them, just passing them as 'OK' after charging to do the work.

The problem is that the cam cap clearance is bigger than the valve settings leading to them not being what you think they are. .002" is usually .000. and why they burn.

 

[Vignobles]

Compression check and for sure run the valves. Besides carbs clogged from sitting then not done valve work is the single biggest cause of trouble on them. The OEM spec too close and leads to some of that trouble, look for no closer than .005" on valves. They burn at the allowable .002" and can on .003" in some cases. Most of the time even the dealers did not set them, just passing them as 'OK' after charging to do the work.

The problem is that the cam cap clearance is bigger than the valve settings leading to them not being what you think they are. .002" is usually .000. and why they burn.

Thanks for youre warning and explaining why, I'll make sure to check this before starting the engine.

 

[Vignobles]

View attachment 6727
It toke more then a month to get the missing parts en clean the carbs, rebuild the front brakes and sorting out the electric on the bike, because that was really a mess left by the last owner.
The engine started at first push on the starter button and I made a trip for checking the gears and the handeling. Tomorrow I'm going to check the compression, bought myself a kit and I'm waiting for sync-kit for the carbs, because the bike doesn't idle well.

 

[Vignobles]

I just did my compression test and it seems that my 3e cylinder is having problems. 1e cylinder 80 psi, 2e cylinder 87 psi, 3e cylinder 50 psi and 4e cilinder 87 psi.
I hope for valve timing to cure this problem but I'm afraid that my valves are burned. The engine isnt smoking and has run 53000 km. Could I try adjusting the valves or is it beter to take the cylinderhead off?

 

[amc49]

Try another gauge, those are numbers for a dead engine ALL of them. Don't use a gauge that simply presses into the hole, worthless. Engine should have been barely running if at all. Any engine below 100 psi is shot. Looking for 140+ to 170. Throttle MUST be held wide open and spin engine until the gauge quits increasing. All 4 plugs removed.

 

[Vignobles]

Thanks amc49 for youre reply. My fault was that I din't open the throttle, so my reading was wrong. After I had checked the valve clearence ( they were all correct) I kept thinking about the compression los of the 3e cylinder. The bike hasn't been running for years so it could be that the piston rings were not doing there job. So I sprayed a bit of WD40 into the cylinder and let it stay for two days. Mean while I changed the oil, and filters and the sparkplugs.
When I started the bike, I could hear the difference, while it first was smoking a bit the refcounter jumped much faster to the red zone.

Just got back from I testdrive, with a very big smile. This bike got his power back and is running like it should.