TOPIC:

I have a 78 KZ650. Im having trouble trying to figure out how to sync the carbs. Ive read up on the forum with the drill bit theory but no one wants to say what ball park the drill bit to use. Also if you don't know the slightest of how to adjust an air fuel mixture or what carb you have to know which screws to turn, you get lost.

These are the carbs I have. I bought a vac. gauge and put it on the little nipple between the carb and the intake but it just kept jumping back and forth between Vac. and Press. Can someone help me?

To stop the needle from bouncing, go to an auto parts store and get a vaccum delay valve. One side of it has for vaccum and the other side has a partial vaccum. The side that you can suck on freely (leave it alone you guys) goes toward the manifold. The other end toward the gauge. This will stop the needle from bouncing but there will be a short delay in the gauge dropping if you open the venturi farther as you are adjusting it. There will be no delay if you close the venturi as you are adjusting it. Just give the gauge a couple seconds to settle to the actual vaccum.
As far as the size of the drill bit, you are just setting the carb to be open the same amount at any given throttle opening. A 1/8 or 3/16 bit works fine. I used 4 bearings from a bicycle front wheel bearing to adjust mine when I was used the mikunis. There is a write up on how I did it in the old forum if I can find a link I will put it up.
Ride safe

From the filebase: (you must be logged in)

Carb Tuning

well I went through the archive and finally found my post here it is, hope it makes things easier for you.


While I've been waiting for my Boyer ignition to arrive I decided to go through my carbs again to be sure they were clean and set to specs. When I put my new exhaust system on last month the pipes on #3and #4 cylinders blued during the very first warmup with #4 being the worst. During the first 10 mile ride on the bike #1, blued a little too. After 250 miles of riding #2 still looks like new. This is all a sign of lean mixtures.
I took the carbs off, completely dismantled them from the rack and started my cleanup. The fuel galley going between the feed tube and #3 cylinder was pretty well plugged with dirt and to #4 was even worse. Going to #2 was clean and #1 was partially plugged. Guess I wasn't getting enough fuel. I have always had popping in the carbs during warmup. So I soaked the carbs overnight and got everything spotless. Reassembled them, and checked all of the adjustments as I was going along of course.
During the initial carb synching I have always used drill bits to set them up, trying to get a uniform drag on them. Then use a vacumm gauge for the final adjustment and they always needed a little tweaking. Being a guy that always says "there's gotta be and easier way" I wanted to do the initial adjustment better. This is the idea I came up with.
I always us a 1/8" drill for the initial adjustment. I came up with the idea to use balls in the throats and let gravity do its work. I used a cardboard box to set the carbs on, they rest at about a 45 degree angle. I take the spring off the idle mixture screw and put it back on. Then I center the synchronizer adjustments on all the carbs. I went down to my local bicycle repair shop and got a new front wheel bearing and took the balls out of it. I put one ball in the engine side of each carb. As you turn the idle speed screw in slowly watch for the first ball to roll through the throat of the carb. Using the cardboard box helps because it makes plenty of noise when one drops. Now lock that carbs synch screw in place. Then, one at a time adjust the synch screw in the other carbs until their ball just fall through. After you have them all set, back out the idle adjustment again. Put the balls back in the carbs and slowly screw the idle speed screw back in. If all goes well all the balls with drop at the same time, if not readjust the ones that don't and retest. Takes a little time but it works.
I put the carbs back on and checked the vacumm and they were all 16" at 1000 rpm. No spitting in the carbs at all. Works for me. Let me know what you think of the idea.
Now I put the Boyer on tommorrow. :D

Ok Ive read this but where are these adjustment screws? What is the screw on the side of the carb?

The adjustment screws are underneath the top covers. Screws with locknuts. Loosen the lock nut and you can screw the slide up or down to adjust them. The mixture screws on the sides of the carbs are just that. They allow more or less air into the mixture as you turn them out or in. For a start after you do the bench sync and get the carbs back on the bike,turn them in just till they stop, don't over tighten them. Just lightly seat them then back each of them out 1 and 1/2 turns.