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Hey Guys, My 1983 Gpz 305 is still running on one cylinder. A couple months back i changed the oil, spark pluggs, cleaned out the carbs and it fired right up. I did however notice that it was only running on one cylinder because when i removed one spark plugg wire, it ran just fine. When i removed the other plugg wire the engine turned off. I checked the spark on the non operating cylinder and was of eaqual spark to that of the functioning cylinder. This ruled out the spark issue. When i removed the filters from the carbs and fired it up i notice there was and outward force of pressure(along with gasoline) coming from the non operating cylinder, carburator. This was strange because there was no pressure nor gas coming from the cylinder that was functioning properly. Could it be timeing......Any thoughts

I wouldn't rule out the spark issue. A plug could fire or appear to fire in air but subjected to the pressure and heat in a cimbustion chamber may not be able to fire or at least not fire hot enough to set off the fuel/air mixture.

Could you have a bent valve or one with less than zero valve lash, allowing fuel/air to be pushed back out of the chamber? Have you done a compression check?

Could there be a float bowl needle valve stuck open, flooding the carb and cylinder?

if running on one cylinder, i seriously doubt that it is timing.

i notice there was and outward force of pressure(along with gasoline) coming from the non operating cylinder, carburator

sounds like a leaking valve.

-Duck

I agree, it sounds like a valve problem.
Hope you get it fixed soon. 'Tis the season for riding you know
Take care and ride safe

Thanks a lot guys.
I ran a compression test and sure enough the faulty cylinder had low compression. Once the head came off it was onbious i had a bent intake valve. It is currently being worked on at Advance kawasaki.I now want to figure out what caused this bending. I dont want to throw the fresh head back on the block and end up with another bent valve? Any Suggestions?

check timing chain and gears.

Obviously bent and only one valve bent?
I would suspect that it stuck in the guide, has a weak or broken spring, or got over revved. The shop may be able to tell you after they've had it apart. Checking the rest of the valve train is not a bad idea while you're in there.

If the cam timing is still on mark, then the valve bent from:

1. lack of clearance
2. weak springs
3. over revving

It would be hard to check clearance at this point so about all that can be done is check the valve springs. I think that on most older bikes, you just check their length which indicates wear but on some, a compression test must be done. I would think that if your springs test out OK, you could just replace the valve and ride.