TOPIC:

I have read some posts about going up 2 jet sizes after each mod. All I know is that after pods were installed my acceleration is weak like it's slipping on the low revs. my mods are listed below...also, most manufacturs say that 550 and under don't need rejetting, is that true?

No, its not true that 550 and under dont need rejetting, atleast not the 550 part. I gained a solid 20-30mph higher top end just going from #92 stock '82 550 jets (tekei carbs, same as your '83) to #95 keihin small head main jets with JUST pods. I had to choose 92.5 or 95 or 97.5, so I went with the 95's and my plugs are nice and tan. You'd probably need #97.5 jets since you have 4-1 AND pods.

The jets are keihin 99101-393 series (call Jeff at z1, he had to order mine)

Although, my acceleration was still excellent with pods & stock jets, my top end was just garbage..Maybe having 4-1 AND pods is screwing your acceleration, or perhaps your clutch IS slipping or somthing else is wrong? If no one else chimes in with better advice (very common, my advice is usually wrong when I think I'm right), I'd give #97.5 jets a try, at somthing like $2 per jet (you need 4, of course), and how easy they are to change, you wouldn't be out much if they don't help.

Pods and 4-1 exhaust raise the power band so even when jetted properly, it may not have as much torque at low RPMs, but should have a lot more power in the top end.

You probably do need to rejet after those mods. I had to on my gpz 550. There is a Dynojet kit out there that should do it. It comes with a needle too.

You might also have to change the needle clips with both mods, Lou's post reminded me of that. I didn't have to play with mine (good thing too, I don't know that the stock clips are moveable). In which case, a dynojet kit would probably be better.

Based on customer feedback, it appears that the stock jet needles work better than Dynajet needles, even though they are not adjustable. Shim them to raise them but the the Dynajet needles from a 550 are the same as used on ALL OTHER displacements, types of carburetors, etc etc, so are pretty unlikely to be a good fit in the bike's needle jets with their skinny profile and lack of taper.

Great info, thanks! I do have the Keyster carb rebuilt in place sorry, but I can't remember by needle position, but I think I put a washer in there to raise it up a hair. I do remember seeing a different taper between the keyster and the stock needles in the area by the tip. Needles should just effect the upper range right?

What about pilot jets? shouyld I increase those too, since it effects lower range?

I just saw that denis kirk has stage 3 jet kits. Does this involve drilling? if I go up to 95 or 93 with z1's replacements do I have to drill as well?

Post edited by: guavatone, at: 2006/04/29 13:15

Post edited by: guavatone, at: 2006/04/29 15:25

I purchased four carb kits and drilled the main jets out to 102 size or 1.02mm with a dremel tool (drill press would have been better probably) and had good results with my GPz. I saved the stock main jets (94's or .940 mm in 22mm smoothbore TK's) for future reference. Replaced other components out of the carb kits but kept the stock needles and OEM size pilot jets. I also drilled out the "plugs" hiding the air screws and replaced them too (part of carb kit).
This "drilling" idea for the main jets came from wired George last summer and saved me the cost of a $100 Dynojet kit!
The bike runs great, although it leans out a bit in a strong crosswind.
Overall, I'm quite happy with the results...great top end.

One of my exhaust pipes was leaking and sealing it corrctly fixed the low range somewhat. I will ride and test more, but so far it rides very rough around 55-60 mph.

Loud, did you drill or just replace jets?

wiredgeorge wrote:

Based on customer feedback, it appears that the stock jet needles work better than Dynajet needles, even though they are not adjustable. Shim them to raise them but the the Dynajet needles from a 550 are the same as used on ALL OTHER displacements, types of carburetors, etc etc, so are pretty unlikely to be a good fit in the bike's needle jets with their skinny profile and lack of taper.

Good to know.


I'm pretty sure the GPZ uses different size main jets than an LTD, well, if the GPZ has #94 mains then I know it does, so 102 would be a bit rich.

I didn't change my pilot jets. Changing the main jets to Keihin small head mains didn't involve any drilling. Unscrew the old jet, screw the new one in, repeat for each carb. The stock jets are hex head, the keihin jets are a slotted head. Larger pilot jets might help your low end a small amount, but I don't think they make aftermarket pilot jets for our TK carbs. Based on Neilage's findings, you could go up to somthing like #100 main jets if you so desired. I'd stop at 97.5 myself, just because you can do that for $8+ shipping, screw em in and be done with it, it would more than likely make a significant difference in your top end. Before I rejetted, my bike struggled to maintain 55-60 mph on flat ground with no wind. It'll run 85 mph fairly easy now, although it feels a little lean around there, which I could change by shimming the needles.

I used the Dynojet kit and it seemed to work great on my 1981 550 D1 (gpz). I bought the kit because I went to UNI pods. I also have a Kerker K-series canister with 4-1 pipe.

I've gone through several combinations of filters, carb kits, and exhausts, and different main jets. I re-did the jetting for each setup. My favorite combination is probably Kerker with airbox. It gives a little more puch off the line than the pods. The pods may give better top-end on the highway, but I live in a city so the nearest open stretch of highway is at least an hour away.

The stock mains are 94. The Dynojet kit came with 98 mains and a new needle. The needle is longer with a little less taper. The starting diameter is the same.

The stock needle would have to move more than the equivalent of a shim to be similar to the Dynojet needle. It would probably need two shims. If you can get the Kawasaki 4D93 needle, that would work well. It's the same as the stock needle, but has 5 notches for adjustment.

Neilage, I would think 102 would be too big for the D1 motor, but you probably need it to compensate for the midrange lean condition since you can't raise the needle.

I always get a medium to dark tan color on my plugs.

Click on this to see the proflies of the needles.

home.att.net/~sherri2000/GPZneedles3types.gif

Post edited by: loudhvx, at: 2006/05/02 02:02

Thanks all, I think I will go cheap and call Jeff tomorrow.

Oh, can anyone comment on there being any disadvantage to going too big. In my case 97.5?

97.5 won't be too big with 4-1 AND pods. With stock exhaust and just pods I went from 92 to 95 and have light tan plugs (just a HAIR on the lean side).

The disadvantages to going with jets that are actually too big are:

1. fuel mileage
2. if you crack the throttle hard, it'll fall on its face then launch you off the back, if it doesn't die.
3. fuel mileage
4. regularly fouled plugs
5. fuel mileage
6. if you were to go hugely too big (like 130+ on a stock bike), you could POSSIBLY wash the cylinders.
7. fuel mileage