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Hello Everyone,

I have a 1975 Kawasaki G5 that I've been tinkering with over the last couple months. I finally got it starting and running great, then adjusted the clutch and am having a new issue.
When the bike is cold (sat overnight), I can pull the choke and it starts on the first kick, idles up like it should and warms up. I can take it for as long of ride as I want, 5 minutes to 30 minutes until the bike is plenty hot. It idles fine, revs properly (occasional bog but mostly only when it's still a little cold) and has good power. If I turn the bike off, I can restart immediately (within 30 seconds), but if I wait any longer, I can kick and kick and it won't fire. Maybe the occasional backfire. I then have to wait until it cools before it will restart.

Jetted with a 22.5 pilot and 80 main (tried a 17.5 pilot and 75 main and starting was an issue and plug showed lean), needle is at 3rd clip. BR8HS plug shows light tan after running hard, then killing the engine.

So far, I have:
Checked for spark when cold and hot, nice blue spark for both.
Cleaned the carburetor twice.
Installed a new carb cover gasket and sprayed outside with carb cleaner to see if I have an air gap both when cold and hot, no change in engine speed.
Checked compression, 130 psi both hot and cold.
After checking the new plug, if I do get it to restart (within 30 seconds) it bogs heavily if I crack the throttle, but doesn't die. The plug went from a light tank to very gray, looking almost like carbon fouled.

The strange part is, it used to start even when hot, without an issue. But after I adjusted the clutch (used to slip under heavy load) this new hot start issue has arisen.

I've spent so much time on this thing, I'm guessing I'm missing something really simple. Any help would be greatly appreciated.

Thanks!
 

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1983 GPz 750, green
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38 Posts
I going to try and give some ideas that may help with the problem. First off what ever the problem its heat related. When the engine gets hot things expand and aluminum expands more than steel.
Double check your compression when its hot. Tighten up the head bolts when its hot, use the correct torque. Loss of compression happens when it gets hot. Second, are the plugs wet when you try to re-start when hot? You maybe 'flooding' it. Thrid, pull the clutch in when trying to re-start. Make sure its in neutral, she wont start in gear unless the clutch is pulled in. There is usually a switch at the lever that disallows starting when in gear if the clutch isn't pulled in. Sometimes these switches are faulty. I'll think of a few more things and post them later. Report back with any new symptoms. Lastly spray it with water carefully to cool it faster and then try starting. Light water mist only.
 

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1983 GPz 750, green
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38 Posts
Just thought you might not understand about the bolts, because the aluminum expands more than steel, often what happens on older equipment is that the aluminum loosens up allowing the steel bolts/studs to move. A helicoil might be needed to keep things tight if the threads are worn.
 
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