KZ550 Main Jet Size Advice Needed!

lol, already done! I went a little larger than recommended (due to limitiations of my bits, .0197" instead of .0145") so they're at about 1 3/4 out, but runs like a champ!

tooocool49723 wrote:

lol, already done! I went a little larger than recommended (due to limitiations of my bits, .0197" instead of .0145") so they're at about 1 3/4 out, but runs like a champ!

That's good to hear they work at .0197" = #50!

At light throttle cruising (like 55 to 65 MPH) keep an eye on your fuel usage. If you feel you are getting low mileage, you may want to reduce the pilot jets.

I'm new the the site and have been reading this thread for a few days and it seems very helpful. I have an 83 KZ 550 LTD with the pod filters and 4 into 1 header. Just yesturday, going by louds drill bit selection for jet sizes...I drilled my main jets out to about a 104 and the pilots to a 37. I put it all back together and now the bike does not run too well. It starts and idles perfectly fine. While on the road, it runs fine up to 1/4 throttle, then it starts to "bog" down, kind of sounds like its going from 4 cylinders to 3. Once I pass 3/4 throttle, it starts to open back up and run normal. Do I need to adjust the needle now that I drilled the main jets? If so how do I go about that? You guys are talking about setting the air screws...where are those? My bike has the TK carbs and on the left carburator plate it says M25 1210. Are we talking about the same carbs?

550rider wrote:

I'm new the the site and have been reading this thread for a few days and it seems very helpful. I have an 83 KZ 550 LTD with the pod filters and 4 into 1 header. Just yesturday, going by louds drill bit selection for jet sizes...I drilled my main jets out to about a 104 and the pilots to a 37. I put it all back together and now the bike does not run too well. It starts and idles perfectly fine. While on the road, it runs fine up to 1/4 throttle, then it starts to "bog" down, kind of sounds like its going from 4 cylinders to 3. Once I pass 3/4 throttle, it starts to open back up and run normal. Do I need to adjust the needle now that I drilled the main jets? If so how do I go about that? You guys are talking about setting the air screws...where are those? My bike has the TK carbs and on the left carburator plate it says M25 1210. Are we talking about the same carbs?

Why 104? My guess is that would be too big. You want more like 99, maybe 100, but if it runs normal at 3/4 and full throttle then I wouldn't worry too much about it being over sized. I don't think that is the problem.

Pilots as #37 is good.

The stock needle is not adjustable. Do you have the adjustable needle?

The air screws are originally covered by a little round aluminum plate to prevent tampering. Use an awl and maybe a small hammer to poke through and pull it out. If you use a drill bit, you risk messing up the air screw.


RE:bogging at 1/4 throttle:
How did it run before the rejet?
Does it pop when you decelerate?
Does it run ok with choke at 1/4 throttle?
Is there a chance one of the pilot jets is clogged with debris. Drilling them makes very little in the way of brass shavings, but if there was dirt in there, yu may have dislodged it and now it's blocked.

Also, it's wise to make one change at a time instead of multiple, since then you don't know which change caused the problem.

RE:bogging at 1/4 throttle:

How did it run before the rejet?

Before the rejet, it ran okay up to 3/4 to wide open throttle. I couldn't go anywhere...It would barely run past 70 mph, making it hard to pass. If i would roll out of the throttle a little bit after being wide open, it seemed to pick up slightly. This kind of told me it was running a little lean. Past 1/4 throttle is was a little rough, but not too bad.

Does it pop when you decelerate?

Yes it pops out the exhaust bad on deceleration... I think some of that may have to do with a small exhaust leak where the collector and midpipe connect...

Does it run ok with choke at 1/4 throttle?

I have not tried. I am assuming the mains are 104 realistically. I used a #60 bit to get 102, but the drilled hole is always slightly larger than your drill bit so I'm assuming its more like a 104...

I don't think my needles are adjustable...probably stock, how can you tell?

550rider wrote:

RE:bogging at 1/4 throttle:

How did it run before the rejet?

Before the rejet, it ran okay up to 3/4 to wide open throttle. I couldn't go anywhere...It would barely run past 70 mph, making it hard to pass. If i would roll out of the throttle a little bit after being wide open, it seemed to pick up slightly. This kind of told me it was running a little lean. Past 1/4 throttle is was a little rough, but not too bad.

Does it pop when you decelerate?

Yes it pops out the exhaust bad on deceleration... I think some of that may have to do with a small exhaust leak where the collector and midpipe connect...

Does it run ok with choke at 1/4 throttle?

I have not tried. I am assuming the mains are 104 realistically. I used a #60 bit to get 102, but the drilled hole is always slightly larger than your drill bit so I'm assuming its more like a 104...

I don't think my needles are adjustable...probably stock, how can you tell?

As you roll out the throttle (reduce throttle) the mixture tend to go lean. As you roll on the throttle it tends to go richer. But not under all circumstances. It depends on RPM, and where the throttle is.

But upper throttle is ok now, correct?

You never had a bog down at 1/4 before?

Have you disabled and sealed off the air injection system? That can also cause a lot of popping if it is malfunctioning (and often do malfunction).

If you have the factory needles, you can tell because they are not adjustable. I don't recommend using shims either. They cause binding on the needle and orifice leading to wear.

You can get adjustable needles in the K&L rebuild kits 18-2462, or the Dynojet kit DJ2305 . The K&L ones match the stock profile. The Dynojet ones are different, but work really well.

I got ya on the #60. I mic the bits because I've seen some variance in their sizes. When I drill I don't dwell inside the hole. Just in and out one time unless I want it bigger. Again, since it seems good a 3/4 and full, probably not an issue. If worried, the K&L kit comes with factory 92 main jets.

You mentioned it sounds like it's on three cylinders. Jetting problems tend to show up as surges and weakness, but not like running on three cylinders where the motor sounds lumpy (like a twin). I would open them up for close inspection again.

The starting point on carb work (after cleaning) should be verifying operational fuel level. On the TK-22s, you don't need any special tools to check the fuel level. You can even do it while they are on the bike. Each bowl has a drain screw and a hose connected. Make sure all is clean. Then all you do is get a larger piece of clear hose (about 4" long) to press over the end of the drain hose. Put the bike on a center stand and make sure it is perfectly level side to side. Take one drain hose with the 1/4" or 5/16" clear tube and hold the clear tube against the side of the carb. Open the drain screw for that carb and put the petcock on prime. You'll see fuel rise in the clear tube up to the level of the fuel in the carb. That's how you know the fuel level. It should stop rising at about 3 to 4 mm below the bowl gasket.

The online manual in my signature shows a good description of the process. You don't have to hold the hose up to the carb you are checking as long as the bike is level.

Also, we need to know exactly where the bogging starts and ends. When I'm testing, I use a cheap (very very cheap) throttle indicator. Make sure the "idle" line is where the carb throttle starts moving. In other words, don't let any throttle slack be in the measurement.

The photo shows about 7/16 throttle. We want to be able to discern down to the nearest 1/16th.

There is a big swing in the mixture ratio from 1/8th to 1/4 throttle. 1/8th is usually the leanest point (like 14 to 15 AFR), and 1/4 begins the range where you are near full rich (like between 11 and 12 AFR).

Check my thread on the o2 sensor.

I have been playing with this diagram showing what affects what range on a TK22, but it is nowhere near finalized, and is subject to change. I copied a diagram I found, and have been altering iot to fit the TK22.

I'm having doubts the pilot jet affects anything near 1/4 because of the huge surge of air and fuel that comes in at 1/4.

I wrote a program that analyzes the changes in needles and clip settings.
It compares the increase or decrease in cross-sectional flow area at each throttle opening for a "test" needle versus a "reference" needle.

This diagram shows the changes from using a K&L needle at clip 3 versus the stock needle (which is the same as clip 2, but fixed).

Notice how everywhere is richer, but some spots more than others. It is important to know, the actual richness change won't be sharp like the diagram. The program only looks at the effects of the needle on the needle jet's exposed area, but that doesn't equate to actual flow. The fuel flow rate will be a much smoother transistion. Also fuel is coming in from other circuits so the lean/rich % scale is not indicative of overall rate changes in fuel flow.

Here is what the dynojet needle does.
In the range that matters most, it is richer than stock, but actually has a low-throttle area where it is slightly leaner. This may need compensating with a pilot jet (very slightly like 34 up from 32). After 1/2 throttle, the difference is negligible.

and here is a comparison of the Dynojet needle at clip 3 relative to the K&L needle at clip 3. (Clip positions are counted from the top)

here is the data i'm basing the program on. I measured these directly using a mic. (The gpz TK22 needles are the same as the LTD and Standard kz550 tk22's.)

But upper throttle is ok now, correct?

Almost...At wide open throttle it tends to bog as well, 7/8 throttle is about the max, and full throttle it goes nowhere. So it actually runs better at 7/8 throttle.

You never had a bog down at 1/4 before?

No, I didn't, but the engine wasn't smooth sounding either.

Have you disabled and sealed off the air injection system? That can also cause a lot of popping if it is malfunctioning (and often do malfunction).

I'm not sure. Where is this located and I'll check it out. The engine does a lot of poping as i'm coasting down a hill in gear.