Wiseco 615cc jetting

I was speaking with Corey Clough from gpz550.com and he suggested that I post my jetting troubles on this forum and said that Wiredgeorge might be able to help out.

I am speaking about my 1985 Kawasaki GPZ 550 with a Wiseco 615cc over bore kit, K&N Pod filters, Kerker K2S 2" straight through exhaust, and Dynojet stage 3? jet kit.

Day 1: just got finished breaking my engine. I warmed her up and headed to the closest freeway on ramp. I took the on ramp at near full throttle and brought the bike up to 9000 rpm in all gears. (looked down and saw 100+ on the speedo so i slowed down). the bike hit hard and took off like a rocket like it never has before. But again when traveling at around 80 mph and in 5th or 6th gear around 5500-7000 rpm the bike doesn't respond unless I open up the trottle even more, then it hesitates, and takes off like a rocket above 7000 rpms. What do you guys think? I believe this a tuning issue, I just need to know which direction to head.

Day 2: The main jet I am using now is a DJ134 designed for stage 3 and "free flowing exhaust" I have kerker 4in1 system w/ 2" pipe straight through the baflle.

Day 3: Well, I got home today and did wat the jet kit said to do for my symptoms. It said to lower down the needle one position to lean out the fuel mixture. I did this and the bike seemed a little less hesitant and only had a problem in the 4,5, 6 gear @ 5000-6000 rpm. The problem also seems to occur when the bike is warm. It doesn't really happen when I first run the bike. The bike also felt like it didn't pull as hard as the previous needle position

Day 4: I adjusted the needle one postion the other direction (richer) clip position #5. It seems to be a little better, but may have lost a little on the top end.

Day 5: Upon further testing the bike is still doing the same hesitation I spoke of before. The bike stutters even when a constant throttle is held when it hits this rmp range. It hesitates between 5-6000 rpms only in 4, 5, 6th gears. It also only seems to do this when the bike is good and warm, like after 1/2 hr. of riding.

Wich direction do you think I should head. Either get an even larger main jet from the kawa dealer (I have no idea how to order the size, etc.) Go up to the last needle position. or try a size smaller main jet that came with the dynojet kit.

Or even look into another direction like synching the carbs. I did get a set of mercury sticks recently.

Do you think it could be the idle mixture screw since it only happens at a relatively low rpm at a very slight throttle.

I further tested the bike today at it's trouble spot and I used scott's suggestion of opeing the choke while at this spot and see what happens. Well when I did this the bike quit hesitating and started accelerating like it should. I was even able to ride around @ around 70 mph in either 5th or 6th gear with the choke open over half way!

The problem is occuring either while slowly accelerating through this rpm range, or holding a constant throttle at this rpm range, when the bike is warm.

I started with the 2nd smallest main jet #DJ116, which had no top end. I then went to the largest main jet with the needle at position #4. I noticed the current problems I am having now and wen to postion # 3 didn' t solve it. As of right now the clip on the needle is at position #5 counting from the top. and I am using the largest main jet that was supplied with the dynojet kit # DJ134.

Which direction do I head next? Needle position #6? smaller main jet (3rd largest jet supplied with kit)? idle mixture screws?

I am going to sync the carbs right now so that option is eliminated

When you closed the choke halfway, you in effect richened the mixture, you need a larger main jet. I ran into something similar on my KZ550, but the engine is basically stock, with the exception of pods and an open exhaust. I have thought about the wiseco kit, if I did that I would go up in jet sizes. I almost went the dynojet kit route, but did not want to shell out the bucks for something like that. I bought mainjets only, at 4 bucks a pop, and played with the needles.

Geesh... not sure what to say about Dynajet jet kits... They give you a couple of sets of main jets and their one size fits all jet needles. You can NEVER be sure what to do on a specific bike since each one has different jetting needs... let me try.


You have Tekei round slide carbs? The stock main jets are #92s I think... Anyway, if you use Keihin small headed jets, they fit perfectly and I DO understand their sizing so START by buying some #102 Keihin small head round jets. They look much smaller but the thread is identical. Then put your stock jet needles back in and try them on the 4th slot. If you have a flat spot, try the 5th slot. If you want to keep fiddling with the Dynajet jet needles, they typically will recommend you start on slot #2 of 6 slots but if you are wanting "stage 3" I would think 4th or 5th slot would be right... Since you have tried these, try the 6th slot.

Since they don't address pilot circuit rejetting, then you are stuck with the OEM pilot jets so that isn't an issue although you REALLY could use a size larger pilot jets... THAT would likely help the flat spot issue.

The main jet is in use when the jet needle is fully out of the needle jet... that means throttle is wide open. Your problems are totally when you are on the jet needle... and a bitty bit from the pilot/main circuits but mostly jet needle in mid-range.

You can also call Dynajet customer support and see what they say... but the OEM jet needles on 4th or 5th slot will also be a good option and using Keihin small head mains... BTW: Here is a point... I picked up a Stage 3 Dynajet kit yesterday along with some other parts. It contained the SAME jet needles as are in your KZ550 jet kit and also #136 and #140 main jets... it is for a 1978-1980 KZ1000 where the main jets vary from #102.5 to #107.5 in stock form... Where do they come up with these main jet sizes. They MUST have different hole sizes OR they are WAYYYYY OFFFF! And use of the same jet needle profiles for all bikes? Yeah... a real custom jetting set up bwhahahaha

Post edited by: wiredgeorge, at: 2005/11/20 17:26

Hello wiredgeorge nice to meet you and thanks for the help.
A possible helpful sidenote I synchronized the carbs. and the bike runs smoother at idle now.

You are right that I do have Teikei carbs (model #k27V), but I looked them up in my manual and they have 114 sized main jets. I have a ZX550, not a KZ550, anyways. The stock needles have a fixed position so I don't believe I can use them.

Should I look into changing the main jet from the dynojet DJ134 I am using now. or try and move the needle postion to the 6th postion to raise the needle furhther?

AHA... CV carbs. The jetting should be about 3 sizes bigger than OEM... so the main will want to go from #114 to about #125 in a Keihin. Again, I don't understand how Dynajet came up with the sizes they did unless their openings are not sized the same as Tekei/Keihin (they are sized about the same). As far as the jet needles, I don't recall how wide the OEM jet needles are but I assume you can shim them. Jeff at www.z1enterprises.com sells Mikuni 1/2mm shims which are very consistant in thickness if you need to try shimming your OEM jet needles but for now, I would try 6th slot on your Dynajet needles. I wish I had a set of Tekei CV needles as I could measure them and could come up with a good needle swap for you... How does the profile of the Dynajet jet needles compare to your stockers? Thinner with less taper?

I will try the 6th position on the dynojet needles. As I looked closer It looks like the 6th position is the closest postion to the stock needle's position. I hope it works I will keep you posted. Let me know if anyone has any other ideas. Here is a pic of the stock needle on the left and the dynojet needle on the right. i21.photobucket.com/albums/b295/NoEardGo...ynojetneedlejets.jpg

Tested more. 6th position not any better. It only does this when the bike is really warm.

The profile of the stock jet is similar except for right off idle where it is a lot more tapered and thin and will be much richer. I would FIRST try and call the Dynojet folks and see if they have anything to say. They will probably tell you to try the 2nd or 3rd slot on their jet needle. If you don't get any good info from them or have already tried what they suggest, try your stock jet needles again... If they are a bit lean, then order some Mikuni jet needle shims and put 2 each under the e-clips. To order, contact www.z1enterprises.com - You could try some washers from the hardware but I suspect they are not made to the same tolerances. Keep us posted!

One last thought... I am not real sure if you have baffles in your pipes or not... is the muffler part just hollow or do you see a smaller tube running down through the inside. A LOT of folks think they have straight mufflers but they are indeed having baffles. If you don't have baffles, you might want to get some and try that...

Post edited by: wiredgeorge, at: 2005/11/21 14:30

I spoke with dynojet today and they said to try position 3 or 2. I will try this when I get home from work. If this doesn't work I will try the stock needle.

My exhaust has a brand new stock baffle that has a vented metal tubing that goest straight through the middle and out the tip. I can take a pic if it helps.

The initial post wasn't clear on the baffle situation. I have seen the Kerker mufflers gutted and the baffles removed. This is a good way to produce flat spots. Give the reclip a try and then try using the stock jet needles.

Well I tried position #2 on the needle and the bike hesitated even worse than before. It hesitated around the same rpm range in even lower gears. It even did it so bad that I had to quit accelerating. I spoke with dynojet tech and this was their only suggestion. They also said that The DJ134 stood for a main jet of 1.34mm ID. The kit also came with a DJ130, DJ116, and DJ112.

Now I will try the stock needle with the DJ134 jet I am currently using. Then maybe try the DJ130, but the bike pulls really well on top end with the current DJ134. What do you think? If this doesn't work I may have to go your route and tune with the main jets you spoke of.