KZ550 Main Jet Size Advice Needed!

It's the two big ports on the valve cover. They connect to a big contraption on top of the engine. You can block it off by tremoving the contraption and connecting the tow ports together. It needs to be airtight. Also block off the ports that the two vacuum hoses went to.

As a matter of fact, make sure all 4 intake manifold vacuum ports are capped off.

Ok, I fixed that problem and now looks like the picture. One thing I noticed while reving it up to 3 - 5 grand with bike on center stand in neutral is some popping back through one or two of the carbs, maybe all four, i'll take a better look. I'm pretty sure it did this before the vacume and jet changes. I didn't take it down the road, but from what I could tell while on the center stand is the exhaust back fire is gone.

Took bike down the road and the exhaust backfiring problem has been resolved...Thanks loudhvx! I'm stil having trouble in the 1/2 to 3/4 throttle range. It hasn't really changed. Idle to 1/4 throttle the engine is deffinately hitting on all 4, runs smooth. Once I roll the throttle to 1/2, sounds like one of the cylinders drops off and the bike has no power. Once I roll to 3/4, It takes off and is running on all 4 and pulling good...Like I said in the last post, while slowly increasing the engine rpm on the center stand, in neutral, I can hear some popping back through the carbs at around 4k rpm, this is in the 1/2 to 3/4 throttle range. Could it be running lean?

Overall, I think idle to 1/4 throttle is fixed, as well as 3/4 to WOT. Right now, the main focus is the 1/2 to 3/4 throttle issue.

While riding and experiencing the problem, would reach down and apply some choke to determine whether performance worsens or improves.

Objective being to help determine whether existing mid-range is too lean or too rich.

Good Luck!

I don't usually recommend it, but if you're going to shim the needle, you should shim the needle retainer as well. this is to prevent the needle from binding and wearing out the needle jet.

Use a guitar string as the shim wire for the retainer.

Tomake the shim wire, I wrap it around an 8mm bolt. That curls it pretty close to the right curve.

When it's done, and installed it should be like this... a single ring inside the slide at the perimeter.

so if I use a shim washer that is 1mm thick under the stock clip, that would be similar to moving the clip down one notch on an adjustable needle? or is 1mm to thick to start with?

550rider wrote:

so if I use a shim washer that is 1mm thick under the stock clip, that would be similar to moving the clip down one notch on an adjustable needle?

Yes, correct. Be sure to use a wire ring in the slide like I have shown, but, obviously, use a thicker wire. Without it the retainer assembly will not sit parallel to the bottom of the slide. It will rock on the needle as a high-spot. When it's assembled, the needle should rotate freely, but have little to no end play.

Also, using shims raises the needle relative to the slide, but in fact, it also lowers the slide relative to the throttle shaft. This simply means you will have to turn-in the idle-speed screw to get back to the original idle position. You will also have to increase the choke's fast-idle setting. This is easily done if you do this mod:
www.geocities.com/loudgpz/GPZchokeScrewMod.html

Thanks to all who posted on this thread!!! It's been a HUGE help...... My question, If I shimmed my needles (I did), Would #37 pilot jets still be accurate? I'm running pods, mac 4into2, shimmed needles, #35 pilots and 98 mains. and it runs great, I'm just scared of running too lean, so I'm considering drilling out to #37's. How much difference do you think the shims (2 small washers) makes? Should I drill them out? once they're drilled I can never get my #35's back, lol.

kenball1980 wrote: ... scared of running too lean....

Could consider spark plug readings at different throttle positions (throttle chop testing) to determine appropriateness of the air/fuel ratio.

Accurate testing requires good ignition (strong and properly timed spark) and decent compression with valve clearances within specs, and carbs in good serviceable working condition (clean passages, correct assembly, proper fuel levels, ample fresh clean fuel supply). Excessive oil burning can also make it impracticable to do plug readings.

Good Fortune!

I think you'll be fine. If it was too lean on the pilot, you'd be popping a lot on decel, and you'd need choke for a long time. If the main is too lean, it will accel like crap when cold, but feel ok when really hot.

The plugs will tell you if you are way out.

Another thing to do, especially since you shimmed the needle, is check your WOT slide position. It should be right at the top of the throat. From the factory it's usually a little higher. This is a good safety trick if you are unsure. By setting the slide above the throat opening, the mixture will get a richness boost when the throttle is wide open at the stop. But ideally you want to find the correct main instead of relying on the boost. If you get the sensation of speeding up as you close the throttle very slightly from WOT, then the WOT stop postiion is likely too high.

I have some details on that in the TK22 site in my sig.