Carb Tuning Help - Have Symptoms need a Cure

So I have a 81 KZ550 the exhaust is pretty much a straight thru 4-2 w/o a crossover, and i now have pods because the old filter was shit.

Now to the symptoms:
- i get some pretty decent backfire while closed throttle decelerating above about 5500 rpms
- if you rapidly open the throttle to full when the motor is under 3000 rpms it will kill the motor
- power seems decent below 1/2 throttle but it really pulls at full throttle

What this leads me to think is that I might be near stoich above 3/4 throttle and running lean near idle and below 3/4 throttle.

So am I correct in my guess? Im new to carb tuning so im just looking for some things to try so that I can get some experience and hopefully get to run really nice and powerful

thanks

DoubleL3 wrote:

So I have a 81 KZ550 the exhaust is pretty much a straight thru 4-2 w/o a crossover, and i now have pods because the old filter was shit.

Now to the symptoms:
- i get some pretty decent backfire while closed throttle decelerating above about 5500 rpms
- if you rapidly open the throttle to full when the motor is under 3000 rpms it will kill the motor
- power seems decent below 1/2 throttle but it really pulls at full throttle

What this leads me to think is that I might be near stoich above 3/4 throttle and running lean near idle and below 3/4 throttle.

So am I correct in my guess? Im new to carb tuning so im just looking for some things to try so that I can get some experience and hopefully get to run really nice and powerful

thanks

To reduce de-acceleration popping, could try enriching pilot circuit by turning adjuster screws 1/8th turn (being clockwise for side-located pilot air screws, or counter-clockwise for bottom-located pilot mixture screws), and lowering idle rpm with thumb screw. If problem persists, may require larger pilot jets.

Mid-range performance may benefit from raising the jet needle (being one clip lower) to enrichen.

As known, carb fiddling is often futile unless preceded by assuring valve clearances and compression to specs, and healthy properly timed sparks, and correct advancer function.

Good Luck!

DoubleL3 wrote:

So I have a 81 KZ550 the exhaust is pretty much a straight thru 4-2 w/o a crossover, and i now have pods because the old filter was shit.

Now to the symptoms:
- i get some pretty decent backfire while closed throttle decelerating above about 5500 rpms
- if you rapidly open the throttle to full when the motor is under 3000 rpms it will kill the motor
- power seems decent below 1/2 throttle but it really pulls at full throttle

What this leads me to think is that I might be near stoich above 3/4 throttle and running lean near idle and below 3/4 throttle.

So am I correct in my guess?

I would bet on it. I would try larger pilots and/or rich the needle position.

Real good advice to make sure the advancer is tracking before you start fine tuning.

All good suggestions...

You may need to rejet completely though.

Get the bike up to operating temperature, then do some plug chops, starting with the main.

Once you have the main figured out, chop for the needle, then set the pilot system.

Its alot of work, but the results will speak for themselves.

You can look up "plug chop" and lots of other jetting info in the filebase.

GoodLuck & Patience!