650/X-2 650SX starts but immediately dies

[03Cummins]

Searched for a bit but couldn't find much. As of recently, my 1990 Kawasaki will die about 2 seconds after starting it. It starts right up but I can't keep it running for more than a couple seconds. The 2 second run time seems pretty consistent too.

I rebuilt the carb, but issue is the same. Even swapped from my buddies carb and still no luck. Just made sure the check valve to the fuel tank is working, also checked for any clogs. Pretty sure I am getting fuel and the carb/fuel pump is good.

Spark looks good, reed valves are good. I'm starting to think its something with ignition or rev limiter. Anyone else had this problem? I don't think its the kill switch, took it apart and everything looks normal to me.

Thanks.

 

[03Cummins]

Swapped the CDI from a running ski and found my CDI was not the issue. Ran a compression check, getting 190psi front cylinder and 170psi rear. I don't know specs on this motor, assuming the head must be milled. Should I pull the cylinder head and check the top end?

 

[Vumad]

I don't have an answer for your problem, but stock compression is 150. Something is wrong with your motor that it's compression is off by that much.

Lets assume for a second that your gauge is correct and that your compression numbers are real. 190, and even 170 are too high for regular unleaded (87 octane). You need to be running high octane pump gas (premium, 93 octane). 190 PSI is boarding the need for race gas. You may be using too low an octane fuel, causing detonation and the motor stops working. Detonation may also be the cause of the loss of some compression in the rear hole.

If you truely have 190 psi, and if you are running regular unleaded, don't touch that thing again until you drain the tank and add the proper fuel.

 

[03Cummins]

I have been running premium in it. I don't know the history of this motor, but it must not be stock.

It was running fine since I bought it a month ago up until a few days ago when this issue started happening. I did notice recently there is some oil in the hull, causing me to think that maybe my crankcase has a leak. I pulled the motor out of the hull but didn't find anything obvious. I saw in the manual about doing a leak check on the crankcase but don't have the tools to do it.

 

[Vumad]

There is something called a leak down test. It checks the motors for any air leaks. The motor should hold X amount of PSI for Y amount of time. It's not something I know anything about.