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Discussion Starter #1
So... I've run into a problem with my GPZ 600R from '86, and me and my mate have concluded that it's a japanese devil that's at fault.

Here's my problem:
Bike was sitting over the winter (had it run warm once a week).
Then back in april when the season "started" i took it out. BUT it's not running right.
When i twist the throttle, the bike starts shaking and is barely pulling it's weight.
The thing is supposed to accelerate with 75 hp, but it feels more like 25

What we've done so far:
Changed the spark plugs.
Cleaned the carbs.
Synced the carbs.
Changed the air filter.
Checked the Coils (resistance was good according to the Haynes book)

I'm at an absolute loss here.
Anyone now what it could be?
Would rather not have to change half of the engine.
 

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You have done a lot, but more information is needed:

1) what did the old plugs look like?
2) what maintenance was done on it before you put it away for the winter?
3) does it idle normally and do all 4 exhaust pipes warm up to the same temperature?
4) how is the oil level and how often does it and filter get changed?
5) with plugs removed and laying on cylinder head, do they all have a good spark when cranked?
6) while plugs are out, you should do a compression check and report numbers back here.
7) when was the last time the valve clearances were checked?

It is also possible that your cam chain has become loose and has jumped by a tooth. If you decide to check your valves that would be a good time to check cam timing.
 

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Discussion Starter #4
You have done a lot, but more information is needed:

1) what did the old plugs look like?
2) what maintenance was done on it before you put it away for the winter?
3) does it idle normally and do all 4 exhaust pipes warm up to the same temperature?
4) how is the oil level and how often does it and filter get changed?
5) with plugs removed and laying on cylinder head, do they all have a good spark when cranked?
6) while plugs are out, you should do a compression check and report numbers back here.
7) when was the last time the valve clearances were checked?

It is also possible that your cam chain has become loose and has jumped by a tooth. If you decide to check your valves that would be a good time to check cam timing.

1: They looked fine
2: Chain was lubed and oil was changed during the winter
3: It idles a bit weird where it jumps a bit in the revs (between 1200 and 1500)
4: The oil is from january and is between min and max.
5: We actually didn't check that.. Will do.
6: Will do if i can get my hands on the tools.
7: febuary 2019 if i remember correctly. and they were actually pretty good compared to the fact that it just rounded 90.000 km

I'm fearing that it might be the Cam chain, only ever fixed that on a single cylinder 125, not exactly hyped to do on a 600 4 cylinder.

Did you check the air box for mice/nest?
Yes, the airbox is clean (apart from a very light layer of dust)
 

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Ok, it looks like the compression check has jumped up the list of importance. To check the cam chain timing is fairly easy. Changing cam timing is not as easy and if you screw it up you can damage your valves. If not confident in doing cam timing then take it to a reputable shop once you have determined that it is off. It should not take more than an hour or two.
 
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