GPZ900 jetting

Hi All

I did a search first before posting this but could not find any posts about jetting for GPZ900.

I have recently bought a project bike, 1984 GPZ900. I do not know anything about the history of the bike.

It has pod filters and twin exhaust with Tranzac mufflers.

I have cleaned the carbies, put new plugs in, changed the oil etc.

The bike starts easy, idles well and pulls to about 4000 RPM really well. 4000 - 5000 is rough then it seems to clear till it stops at about 8500.
The carbies have 145 main jets which I would have thought may be too big.

Was just wondering if anyone had a similar setup and what size jets they were using to help sort this out. I really want to get her back on the road.

Thanks in advance.

Not sure why you would put bigger jets in - I would have thought just richening up the mixture for the pods would be all you'd need to do? I'd have a look in the book for teh standard jet size and go back to that for starters. Are you saying the rough running stops at 8500 or the revs?

NO the rough running stops at about 6000 then it only revs to 8500

Drop the needles 1 notch, that will tell you which way to go, if its clearing up high in the revs, then the main jet is probably ok.

......Drop the needles 1 notch, that will tell you which way to go, if its clearing up high in the revs, then the main jet is probably ok.......

I'd actually go the other way mate - lift the needles 1 clip position. That rpm range old mate is having the issues - is right on the transition point to the main jet. Lifting the needle will richen it up a bit which it probably needs because its running pods.....

145 mains are pretty big - stock on these bikes was 132.5. They go up in increments of 2.5, so you are 5 sizes up on stock still running twin pipes, that is probably 2 or 3 sizes too far.

I would suggest using 135's or 137.5's. These should get the motor revving out properly at high rpm.....at the moment it is just running far too rich....