Idle speed.

I have a 1977 KZ650B1. It has the slide-type (not CV) carburetors. I had to split the bank apart this spring and replace the O-rings for the center T-shaped fuel tube. So I broke the carbs down into two pairs of two after removing them from bike. This required removing the top caps, throttle arm, and the slides from the carb bodies, the the throttle cable arm and the idle adjuster screw.

Replaced the O-rings, put everything back together and the carburetors are leak-free. However ... now I can't seem to get the idle speed to drop below 1500-1800 rpm. Even if I back the idle adjuster all the way out (as in off the carb bodies) the idle still remains high.

What would cause this? Intake boots not sealing? Carbs not level? (I run pod filters ... no airbox).

Bike ran beautifully all year last year. I did the carb rebuild after pulling it from storage this year.

all the caps are back on the synchronization ports? how about the fuel tap port?

double check that you have freeplay in the cables that would be the first place to look.

I checked the cable slack and even loosened them up to see if that was the culprit. No luck there.

I pulled the carburetors again and put them on the bench. I found a couple of screws in the carb tops that were not tightened down. That might be it ... but it is very late here. I made sure all four carb tops were snug and put the carb bank back on the bike. I'll kick it over tomorrow and see what's what.

It lights and runs great ... it just won't drop down to a nice, smooth idle at 1,000 rpm or so. It has to be something simple I hope so we will see if giving the carb tops a proper fit makes the difference.

what are your air screws set at.

Wondering if bench-synced during reassembly without first assuring the thrumb idle screw in mid-position, which allows further lowering of slides to reduce idle rpm.

Good Luck!

Arrrrrg. Bike is still not settling down to a low rpm. I can still back out the adjustment knob and it stays at 1400 rpm or so. I have the old carb rack with the air adjustment screws on the side of the carb, not the bottom. They are set to approximately 1 1/2 to 1 3/4 turns out from seated. I didn't mess with the jetting when I took the carbs off to replace the fuel tube O-rings.

My carb boots look good. I checked the cables again, plenty of slack there so it's not hanging up that way. It revs just fine, you can blip the throttle and up and down and it rises and falls smoothly but it just won't drop down to the recommended 1000 rpm idle speed.

I put a new fuel line on and a new in-line fuel filter last night. But that shouldn't change things like this! What is really annoying is the bike ran great all year last year, then I basicall replace a few 50-cent O-rings and now I have this hassle.

Do I need to re-sync the carbs? Could pulling the throttle shaft and then re-attaching the slides mess it up like this?

you have air screws try turning them in to about 3/4 of a turn it will cut off the air getting to the pilot circuit. .

Okay I tried the bike again late last night. It started fine, idled nice for a few minutes, then when I gave it some throttle it raced up to 4000 rpm and wouldn't drop back down. I checked the throttle linkage, it was shut.

When i rebuild the carburetors I removed the following:

Top caps
Rubber end plugs for throttle linkage arm
Throttle linkage arm
All four carb slides
Throttle return spring
Throttle cable bracket
Idle screw
Carb mount plate (big plate that all four bolt on to)
Center T-shaped fuel tube

Visually, everything looks good when I remove them. I did not monkey with any of the jets. When I re-assemble them I didn't miss any screws or leave anything loose.

Could I get some kind of air leak from the end plugs? Or the seals along the passages for the throttle linkage arm? Or am I chasing the wrong symptom?

Well, it is not the carb tops (you remove those to do a sync on my style of carburetor). Ditto the end plugs. The sync ports are all sealed with their plugs in place.

I did not do any type of adjustment to the slides when they were apart. I just bolted the throttle arm/carb linkages and throttle cable pulley back on (after making sure the cable pulley was in the fully closed position).

Right now I am thinking something is amiss with either the boots when I re-seat the carbs, or i've missed a step when re-installing the carb throttle linkages. BUT as I said the bike will start with the choke on, idle and rev down when the choke is pushed off. After a few minutes you can blip the throttle, and it gradually will rev higher and higher until the motor is humming away at 3500 or so. Twisting the throttle at this point makes no difference to engine speed so it isn't the cables. ???

yes i think you answered your own question it definitly sounds like air leaks that is why the rpm is going up when it gets warmer.

Air leak ... yeah, but from WHERE?

Carb boots? Is there some trick to getting a good seal once they are yanked off? They are so thick it seems unlikely I've cracked one. I haven't pulled them from the cylinder head, either. I'm open to some ideas at this point. I suppose I could hit the intakes one at a time with a little carb cleaner or WD40 and see if i get more revs and some smoke (i.e. - the fluid is getting pulled in). Other thoughts?