Dual screw type adjustments and rough idle

I'm not sure how much of these symptoms are related and I thought it was carb related but I'm not entirely sure. Please tell me if I'm entirely off base.


I recently replaced the 4-1 exhaust on my 77 KZ650C1 which had been damaged in an accident with a decent looking set of stock 4-2's. Out of curiosity, tried to start and had no luck (turned but never fired up)

Pulled the carbs, (looked extremely clean on the inside but went through with kits from Z1 anyway). Went from 102.5 to 97.5 on the main jets. Was already at 15 for the pilots so just replaced them, although they looked clean. Replaced everything else from the kit but I didn't touch the floats. Needle clipped at 3.

The manual is a little confusing for me as it references pilot screw type and air screw type but my carbs have both so I followed the steps for both (2 turns out for the air screw, 1 1/8 for the pilot screw) :blink:

Did a bench sync and reinstalled and it fired right up. I went to fine tune the pilot and air screws and found that turning the pilot screw in (clockwise) half a turn caused the revs to increase notably but then I can screw them all the way in without any difference. If I set them back to 1 1/8 and instead adjust the air screw, I found that a half turn out (counterclockwise) increases the revs, but then the revs don't decrease when I continue to turn counter clockwise.

From my research, it sounds like I'm running rich. Do I need to coordinate both screws? Am I missing some obvious step?

I put some gauges on and found that I was extremely close to synced and needed only extremely minor adjustments.



For a while now I've had a rough idle that I hadn't cleared up and had hoped going back to a stock configuration and thoroughly cleaning the carbs might remove some of the variables. The idle is still rough but only below 1200RPM. At 1500 RPM, it sounds smooth and fine, just a little fast. When I dip below 1000, it begins to gallop slightly and there's an loud inconsistent clacking sound from low on the engine. From previous discussions here and the fact that it only happened when the idle roughs up, it sounded pretty logical that it was just "slack" being picked up.

It's hard to describe...would it be helpful to record it and post to youtube?


Sincerely,

-Confused in Boston

Do you have a manual?

You probally need to start at the very begining of troubleshooting... Compression (Leak down test is better), Spark power, valve lash, completely dissasembly carburettor and rebuild it. Set floats to proper default level. Set air/fuel screws to default setting. Blah blah... :laugh:

Gotta remember, those air/fuel screws are for fine adjustment only. You need to have the jetting correct first.

If you have close to a stock setup, I would leave the pilot screws alone (default) and just adjust the air screws.

With multicarb setups, you need to adjust the screws on all the carbs at the same time. Turn them all 1/4 in/out at a time. When you find highest idle, then start turning them 1/8 in/out individually to find even higher idle.

If the idle stays the same, or does not increase, leave it.
Blip the throttle hard to higher than 1/4.
If the idle drops below the previous set point your too rich. If it hangs for a bit above the previous set point your too lean.

Good Luck!

You'll know its right when she pulls from the curb smooth and confidently, and contimues to accellerate consistant and powerful with graduating throttle input.

TeK9iNe wrote:

You'll know its right when she pulls from the curb smooth and confidently, and contimues to accellerate consistant and powerful with graduating throttle input.

Well, it does that now...It takes off smoothly, sounds smooth through straight onto the freeway and accelerates hard and fast without hesitation at any point. It's just when I'm at a full stop and try to set my idle below 1500RPM's that I have a problem.

I've been looking at my manual but I wanted to get some input before I went further as the manual makes a repeated point of the fact that I should have one screw or the other but not both. Before I started poking around further, I want to make sure I eliminated the possibility that I've just not adjusted them properly.

According to Kawasaki dealer bulletin 10/21/77:

KZ650s were recently changed from the pilot screw carbs to the air screw type. Several hundred units were shipped with cabs that have both. When tuning these carbs, turn the pilot screws all the way in, and adjust the air screws as normal.
This was direct from Kawasaki, so worth a try. It would sure minimize the suffering trying to adjust both if it works out.

as ron just stated above. if you have both... mix screws all the way in and adjust with the air screws. all the new kits specify this too.

Virii wrote:

It's just when I'm at a full stop and try to set my idle below 1500RPM's that I have a problem.

I really don't think its your carbs then. There shouldn't be any "slack" anywhere in the engine. Everything should be tight and smooth. Only a loose cam or primary chain would cause a slacking/clacking, and both are cause for concern.

If they have worn severely beyond thier service limits, they need to be replaced.

The cam chain tensioner could likely the culprit. Whens the last time you serviced it? It needs to be compressing the cam chain fairly snug. If it is loose, it will reduce power, cause clacking/clanging at low rpm, and cause bike to not idle/or idle erratically.

You can clearly see the tensioner assembly in this pic.

It needs to be operating properly. Look in your manual for the removal/check/installation.

I think this will solve your problem.

Good Luck!

RonKZ650 wrote:

According to Kawasaki dealer bulletin 10/21/77:

KZ650s were recently changed from the pilot screw carbs to the air screw type. Several hundred units were shipped with cabs that have both. When tuning these carbs, turn the pilot screws all the way in, and adjust the air screws as normal.

Ahhh, good to know, thank you. I didn't find this in my manuals or on the kits.

Using that, I believe I have myself dialed in properly now so the assumption that it's not the carbs seems pretty sound ... which means I'm probably now in the wrong forum.