Replacement valve sources ,'82GPz750

Hate to type type long sagas and hair-brained thoeries (if they wrong... or genius if they are correct--unlikely). It is somewhat possible that it has mis-adjusted, tight valves. The bike starts and runs on all four cylinders for about 5 to 10 mins. After that it seems to drop cyls intermittently.

Could it be tight valves that are getting tighter when hot and then wont seal causing the cyl to not fire until the valve cools and then is able to seal again for a while ? As I mentioned earlier I did the overrev incident the first time I fired the bike up so I am unsure how it ran prior to that. I cleaned the carbs properly,and they have the plugs installed in them. I've swapped all the electrics and that effected no change either.

The valve adjustment is slightly suspect due to their being orange silicone on the valve cover gasket....most likely no proper mechanic would leave that showing !!

OK now we're getting somewhere. If the bike runs fine for the first some minutes and than starts to run rough, It may be the valve adjustment. Your ship gaps may be too small. as your engine heats up the valve lengthens and the tolerance gets even tighter. This will cause the valve to stay cracked open if the gap was too small to begin with. It is better to have a gap a little too big than one that is too small. If you had a bent valve or valves you would hear it in the exhaust or intake depending on which one is bent. I would check the gaps immediately before you burn the valve faces and valve seats.

Ok then, my theory may be valid !!

I will check that , hope to have some time this weekend.


..........and my GPz305 does the same thing..

Boy, that would be a lot of bent valves. Is that a coincidence? :ohmy: :blink:

I wasn't able to check as many things on the 305 because I didn't have duplicate electronics and I hadnt yet bought my compression tester. It was acting in a similar fashion though.

It's been sitting for about 3 years now though..
...new issues I'm sure will result from that. My projects seem to progress on a geologic time scale. The 305 was bought as a girlfriend bike....she's long gone, but I still have the bike.

like some others said, first test compression, it will be pretty low with a bent valve, if bad, lift cover and check cleareances. If any has an abnormally big clearance, then yes, that one is bent (and is not seating fully, hence big clearance)you should hear also some very loud tappet noise if its bent. Dont ask me how i know

A bent valve will also let out gases during combustion, you should hear some sort of whistling sounds in some of the pipes.

Would be surprised if they are, a dohc is pretty resitant to valve float and your motor is stock i'd guess, no high lift cam or dome, shouldnt really happen.
there are so many other reasons for rough running....

TG

Finally got around to checking the clearances . They were all tight except for one intake.

My .0015" feeler wouldn't fit into any of the exhausts. All the exhausts had #250 shims in them. I swapped them for the #240's that were in the intakes and I was able to get some clearance measurments that I could use to determine the proper shims. After swapping the 240's in I was able to determine that with the 250's I had the following clearances -.001, .000, .002 and .002.

The intakes were all at .0015" , except one that was .005". Shims and gasket are on the way, hope to get to it this weekend

I think that you will find a big difference now. I hope that you did not burn any of the valve seats with the bleeding you had. After you re shim them and seat them for a few miles, you may want to check them again and than do a compression leak down test.

Yeah, I hope that I didn't cause any damage. I rode the bike probably less than 100 miles, but not sure about previous owner. We'll see.

I got it shimmed and it runs. Now the fine tuning begins. It's idling high @3000-4000 and it returns slowly to that speed. It's also a little hesitant from down low, but does clear up and pull well all the way to redline. I hope to spend some time on it this week, I have a feeling that the intake manifolds may not be sealing.