SOHC.co.uk Forums > CB500/550
Low compression but the bike runs fine?
alexdecker:
Hey
Just finished a tune-up of my CB550F2, and carb synced it in the end. My new compression tester just came in the mail today, so wanted to try it out. I am surprised that I get really low compression on all four cylinders though! Between 60-70 on all of them. I tested the bike while it was warm, and had choke and throttle fully open.
I have a clip of the bike idling (warm, as I took it right after the compression test), and it idles well and runs well, and not rough at all. So why the low compression??
https://youtu.be/3XW8BiG1dDk
Any help or advice is greatly appreciated.
- Alex
alexdecker:
No smoke at all. And the motor is running fine at low and high speeds…
Nurse Julie:
With all 4 reading low but very close to each other and the bike is idling / running fine, I would suspect the accuracy of the guages.
alexdecker:
It's a no name brand I think. You can see the tester here: https://www.vidaxl.dk/e/kompression-tester-til-benzinmotorer/8718475816249.html?gclid=Cj0KCQjw4eaJBhDMARIsANhrQAC0pyvjfPzjCYf-QU30mMlAD0I0k3xOdMCAamOyiaTZqdA8_jaue1kaAh_hEALw_wcB
I do have an oil leak on each side of the head (the oil galley because of too small O-rings), but that shouldnt affect the results that much, should it? I will try the oil drop trick. Though I could only warm the engine up and get the same results.
Also, do all spark plugs have to be off at once?
I just set the valves, so that should not be it…
McCabe-Thiele (Ted):
When I checked mine on my 400/4 last year (unrestored) after it's first run for 12 years mine were all around the 80psi mark that was with all the plugs out and throttle fully open with no air cleaner in place. Hot start was good but a swine from cold so hence the strip down.
If it goes okay & starts easily I would not worry about the readings as the gauge is probably not very accurate. One of the disadvantages of checking them is you are likely to be disappointed.
Navigation
[0] Message Index
[#] Next page
Go to full version