Cold Cylinder #2, '81 KZ750 LTD

Injected wrote:

You need a minimum of around 100 PSI for combustion to occur. I would also check valve lash while your running thru all the rest of a basic checks.

Wookie58 wrote:

Have you tried setting the petcock to "prime" and blanking the vacum port on #2 carb ?

Wookie58 wrote:

Have you tried setting the petcock to "prime" and blanking the vacum port on #2 carb ?

Wookie58 wrote:

Progress then, looks like a vacum leak through the petcock. Sounds like you also have other air leaks given the "hanging revs"

SnyperX wrote:

Wookie58 wrote:

Progress then, looks like a vacum leak through the petcock. Sounds like you also have other air leaks given the "hanging revs"

I already have new carb intake boots as well as new airbox boots. Do I need to start spraying WD-40 or starter fluid in places? 

Wookie58 wrote:

SnyperX wrote:

Wookie58 wrote:

Progress then, looks like a vacum leak through the petcock. Sounds like you also have other air leaks given the "hanging revs"

I already have new carb intake boots as well as new airbox boots. Do I need to start spraying WD-40 or starter fluid in places? 

You can try WD40 but it tends to be inconclusive unless the leak is huge. Have you tried slackening the throttle cables then operate the throttle linage by hand (this will rule out a mechanical or cable adjustment issue)

SnyperX wrote:

Wookie58 wrote:

SnyperX wrote:

Wookie58 wrote:

Progress then, looks like a vacum leak through the petcock. Sounds like you also have other air leaks given the "hanging revs"

I already have new carb intake boots as well as new airbox boots. Do I need to start spraying WD-40 or starter fluid in places? 

You can try WD40 but it tends to be inconclusive unless the leak is huge. Have you tried slackening the throttle cables then operate the throttle linage by hand (this will rule out a mechanical or cable adjustment issue)

Wookie, I did try this and it seemed to operate fine. If I pushed the throttle more closed using my hand it made the engine sound like it wanted to die. So in my mind throttle linkage is not an issue. The bigger issue that is now scaring me at the moment is that all 4 cylinders are showing a cold compression level of only about 100 psi for all 4 cylinders. I did re-shim the valves and hoping that's not impacting anything. Terrified the top end if going to need to come off and if machining is needed I don't know what I will do. No real good machine shops around.

84_GPz750 wrote:

@SnyperX I just found this thread but have and am still having all of the exact same issues you describe here with my GPz750. Cold cylinder #2, hanging revs once I was finally able to get it to start and idle, charging issues, and currently I'm fighting poor running just off idle. 

I'll be keeping a close eye to your progress to see if you find a resolution that I can apply as well. 

For my hanging revs, I found a combination of the throttle cable binding up and not fully returning, and the angle of the throttle cable holder bracket needed tweaked. 

Best of luck on your project!