Honda CB750 (and CB450) Compression Test Results

Posted by 750K8 on Feb 21, 2013; 6:15am
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/Honda-CB750-and-CB450-Compression-Test-Results-tp4036911.html

So I'm at the point where I'm questioning if my bikes are in need of a rebuild, or if my methods of testing are poor.

I have a 1978 CB750k with 12,000 miles. Bought it used off eBay. Runs really good. Idles awesome. Kickstarts really easy. It even feels like it has good power.

This was with a compression meter that screwed in the spark plug hole:

Cyl #1: 125
Cyl #2: 110
Cyl #3: 110
Cyl #4: 110

* Wide open throttle
* Didn't open the choke
* Can't remember if the engine was cold or hot during testing.
* Dry numbers.

You can hear the bike here:
http://www.youtube.com/watch?v=HTrkFKirg-E

I just acquired a 1972 CB450 with 22,000 miles. It was parked for several years, and ran a couple times last year by the PO. I did some rudimentary tuning (adjusted the idle, points). It now idles pretty good, but still needs additional tuning.

This was with a compression meter that you press up to the spark plug hole:

Right cyl: 120 PSI
Left cyl: 110 PSI

* Wide open throttle
* Opened chock all the way
* Cold
* Wet numbers

So I'm starting to question if both engines are tired. I've read in a few places that if it's under 150PSI, then it's time for a rebuild. That would mean that my engines are long overdue.