GPZ900 jetting

[bazbaz666]

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.

[pkay]

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?

[bazbaz666]

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

[s man]

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.

[Gosling1]

......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....