TOPIC:

I'm tuning my KZ650C2 carbs, Kerker 4-1, slightly opened up airbox.

I've up-jetted the main to 105 and it runs really well from 1/2 to full throttle, but is somewhat sluggish from idle to 1/4.

Question is, with 4-1 exhaust and freer flowing airbox, does the air screw need to be turned in more than the 1 1/2 turns out specified? I'm at 1 1/4 turns out right now and need to go in more, is this normal?

Looking at the pilot system this doesn't make sense to me.. help?

I don't know much but i only use the air scews as the final adjustment, folling the manaul, turn each screw to find the fastest idle and then readjust main idle to the starndard 1000 - 1300 rpm setting.

I always start by balancing carbs first, then idle screws then main idle. Any help to you?

What did you do to the airbox? If your airbox and jet setup is not good you're going to have a flat spot whatever.

Post edited by: Cactus, at: 2007/03/13 09:21

If your screws are on bottom of carbs, they control "fuel", called pilot screws, factory setting is 1 1/8 turns out. If screws are near top of carbs, they control "air", called air screws, factory setting is 2 1/2 turns out. Pilot screws control fuel, so in to lean and out to richen. Air screws control air, but in reduces air which richens and out adds air which leans. Confusing? Makes me think a lot explaining it...

I have a 1977 650B1 model. I dumped the stock airbox (old and in bad shape) for 4 pod filters. The exhaust is still stock. My jets are: #15 pilot, #105 main, air screws 1 1/2 turns out. It is still a little rich so I'm twiddling with the air screws to get the balance right. But I don't have any hesitation or other problems, I can roll away from a stop and get to 60 - 70 mph fairly quickly and smoothly.

Take a ride and check your plugs. Are they dark and sooty? Too rich, add lean out the mixture (add more air) by backing out the air screws 1/2 turn or so. Are they white maybe even with some hot spots? Too lean. Turn the screw in to richen the mixture. You want a light tan or gray look to the plugs after some use.

Another seat-of-the-pants check: if you get on the gas and it hesitates, you're running lean because the carbs aren't getting enough fuel when you snap open the throttle. If you roll off and the rpms hesitate before dropping or it surges, you're too rich.

Any time you deviate from stock it will take some trial and error to get everything close to right.

Thanks for the tips, I'm just going to keep tuning the air screws until it runs right - even if this means exceeding the 1 1/2 +/- 1/4 turns specified in the service manual.

At about 1 1/8 right now and I'm pretty close.

Re-checking the timing also helped.

Yes, keep in mind the # of turns specified in the manuals is for a completely stock bike. You will likely wind up a bit outside that range.

I'd say if you go more than 3 turns out your jets are too big, if you wind up going less than one turn out you are jetted too lean (too small). Good luck!