Doesn't sound good

MBx2

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Hello


*Edit. The clutch handle is held down in the clip so it's not engaged.
I have a 1983 CB 750 F2 RCO4

I have a worrisome sound from my engine that appeared a couple of days ago (or at least it is more pronounced). I've used a screwdriver and also a tube to try and figure out where the sound is coming from and I think I can hear it the clearest on top right where the valve cover is.
I also have a lot of condensations and soot from my exhuast (it's not in particular good condition).
It also vibrates a bit above 4000 rpm (which I thought was because of sync and timing).

What I've done:
Cleaned carbs following MacGregor Carb Cleaning Services "Honda Carb Manual rev G" and plugged the air cutoffs.
Replaced spark plug caps and wires
Cleaned contact surfaces
Measured valve clearance and adjusted it
Compression tests
Adjusted timing
New exhaust gaskets and a new pin bolt (broke one off on cyl #3)
Synced carbs
changed oil
Adjusted cam chain tensioner at idle according to the CB750 manual.
Removed and had a look at and cleaned the starter clutch

After all of that I have taken it for a short test run but I noticed that it was leaking a lot of oil from the tach gasket and only during load. Unfortanetly the oil lamp lit up just as I was in-front of the garage. So I replaced the gasket and changed oil, I didn't notice any metal when I drained the oil though the plug at the bottom. I ran with 10w40 mineral oil and added some zinc.

Later I took it for another test drive and I noticed it was vibrating when I was driving a bit faster. I also heard a ticking sound which I thought was the exhaust. So I ordered new exhaust gaskets and a new pin bolt because I broke one off on cyl #3. After I mounted the exhaust I took it for another test runt and it was still vibrating so i tried adjusting the timing again, Still vibrations so I decided to borrow a sync tool and I balanced the carbs. But I had to bottom out the screw between carb 3 and 4 for it to be ok.

1660167488025.png


Here's a picture of the exhaust "leakage", it doesn't smell so i suspect water and soot. Still it ain't good, the system is patched and a bit rusty.
1660168515912.png


This is how my spark plugs looks at the moment. I think I've run at idle for a while and before that I've been driving.
1660167173884.png

Bellow is the valve measurements I've taken and corrected (the ones in bold are shimed) I also added the compression test I've done. I put everything in sequential order

CylinderFirst measurementSecond valve measurementCompression test cold after new shimsCompression test warm after new shimsThird measurement when the problems were most noticeableLatest compression test after running the motor for about 800km
1 intake15mm, 9mm13mm, 10mm170167,514mm, 13mm165 (weaker battery)
1 exhaust10mm, 11mm10mm, 10mm10mm, 10mm
2 intake14mm, 15mm14mm, 13mm172.516517mm, 17mm170
2 exhaustToo tight to measure, 8mm15mm, 13mm17mm, 16mm
3 intake12mm, 8mm12mm, 12mm167,516515mm, 17mm175
3 exhaust10mm, 11mm12mm, 12mm10mm, 10mm
4 intake8mm, 14mm14mm, 15mm170162,5 (weak battery)16mm, 16mm185 (started measure with cyl 4)
4 exhaust13mm, 13mm14mm, 13mm16mm, 15mm


My next plan is to adjust the valve clearance, curl up into a ball and rock forward and backwards and hope it helps. Maybe having a look if there's something with the exhaust.
 
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MBx2

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I have given a bit more of thought and I think I need to have a look at the ignition as well (judging by my sparkplugs together with my valve clearance). I will do a spark gap test together with valve clearance and another sync when I have the time and update the thread. But I don't want to do too much of I need to split the engine for a bigger overhaul.
 

MBx2

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Thanks for the reply. I fill some oil and see how it effects the sound. And after the valve clearance, timing and sync I migh empty the oil and remove the sump to look for evidence.
 

MBx2

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Ok! Thanks again. I'll update when I've had the time to check. And if I remember I'll take some pictures
 

kirky

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my 1979 750FZ DOHC vibrates a bit above 4000rpm as well. but the engine is very quiet according to my mate who has owned a few. so this could be normal, anybody know if it is?
 
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