1989 Kawasaki ZX600 carburetor setup issues | GTAMotorcycle.com

1989 Kawasaki ZX600 carburetor setup issues

H

helloworld

Well-known member
Good day gents, ran in to some issues with my current project, it seems that if I do one step forward, I will have to go 2 backwards after.


Bike is 1988-1989 ZX6C model.
Modifications:
* pod airfilters (airbox removed), i know, I know... I've been warned about it multiple times...
* 4 in 1 exhaust with delkevik can
* Had stage 3 carb kit installed.
* Engine top end rebuilt

Current carb setup, 40 pilot jet (35 stock pilot), 110 main jet, stage 2 needle.

Issue, starting.... ohh the pain I have with it starting.
After updating to 40 pilot, its a lot easier, as with 35 it would only turn over and would not even fire up unless quickstart was used.
With 38, had same issues, went to 40.
Have 2.5 turns on the mixture screws under each carb .

The issue presents itself following: when I try to start the bike, it will not. What i have to do is, I open up the idle screw about half a turn, the bike starts but idles at about 2k (once warm - 1.5)
The main problem with that, when i roll-on throttle from idle to 5-6k then let go, I have a hang around 2.2k, indicating its lean.

So, my main question is, should I first play with mixture jets and put them out to 3, 3.5 turns, or should i up the pilot jet first to 42 and go from there?


Mid-rangeand top on the bike are good, puts out 82-83 horses on the dyno, which is correct with stock manufacture specs for the 1989 year: 84 hp @ 11000 rpm (rear tire 74.8 hp @ 10300 rpm )

Any ideas of how to troubleshoot such behavior?

P.S. going back to an airbox is not an option :(

 
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helloworld said:
;(( no carb gurus here? damn....
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As you already know, any carb guru would tell you pods are the devil. I have never heard of a single bike that liked running pods, but they do look cool.

I am not a carb guru, but as the majority of your problems are low in the rev range, I would go up on the pilot jet (and down on the idle speed once it is happier).
 
Individual filters don't usually screw up the idle and slow circuits (much). Mid-range is another matter.

Warm starting and idling is mostly idle mixture screw setting and partly slow jet and float level. Make sure the float levels are in the ballpark before going any further. Try 3 turns out on the idle mixture screws. If this results in a high idle speed, and turning the idle speed screw down doesn't bring the idling speed down (A) make sure nothing is mechanically preventing the throttles from shutting against the idle speed adjustment screw and (B) that the carburetors are synchronised properly and (C) that you don't have vacuum leaks - check rubber boots between carbs and engine, check any vacuum hoses that connect to the vacuum ports and make sure the rubber plugs on unused vacuum ports are in place.
 
Thanks for the input GreyGhost and Brian!

* make sure nothing is mechanically preventing the throttles from shutting against the idle speed
yep, done that, no issues there.

* that the carburetors are synchronised properly
that has been done last year after carb rebuilt as well, but it should not affect initial start, as in my case its first start that makes it difficult, after that no problem at all.

* that you don't have vacuum leaks (check rubber boots between carbs and engine)
Had a vacuum leak on the carb to intake, but that has been fixed over winter with new rubber boots.

* check any vacuum hoses that connect to the vacuum ports
gravity operated, the vacuum hose from carb to gas tank has been removed and free flow fuel tap installed.

* make sure the rubber plugs on unused vacuum ports are in place
yes, all new snug rubbers installed, tested it by spraying quickstart on them, idle doesnt move at all




Also, during recent carb changes, I've noticed that my mainjet has been changed from 114 to 110 during the last year carb clean and sync. But mainjet should not affect my starting at all 8-\
 
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Quick question to you guys.

If pilot mixture screwes fix the lean issue once opened up one more turn, are they adding more fuel or air?

I'm asking, because mixture score on side of carb adds air. Pilot jet adds gas, pilot mixture seems to be adding more gas as well, but at same time, is there more air being added through it?

Asking, because certain setups they seem to be producing different results when playing with pilot jet size and pilot mixture
 
The idle mixture screw adds an emulsion of fuel and air - but it is more fuel than air, so turning the screw out opens the idle mixture port more and makes it richer.
 
Brian P said:
The idle mixture screw adds an emulsion of fuel and air - but it is more fuel than air, so turning the screw out opens the idle mixture port more and makes it richer.
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OK, great, so it does add the air as well, Thanks!!!

Need to go on the pilot jets one more size then, other ways the idle is too high.

Thanks for all your input Brian, I owe you a coffee or pint... Whatever! :)
 
helloworld said:
[...]
The main problem with that, when i roll-on throttle from idle to 5-6k then let go, I have a hang around 2.2k, indicating its lean.
[...]
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You have this backwards. If the RPM's hang up when you chop the throttle, it is rich. You can duplicate the problem by holding the choke open a bit to confirm, for your own piece of mind. The directions Brian gave you were correct. Once you get it starting and idling properly you can begin to adjust the mid-range (jet needle - both taper and clip position, and needle jet sizing).
 
LPakkala said:
You have this backwards. If the RPM's hang up when you chop the throttle, it is rich. You can duplicate the problem by holding the choke open a bit to confirm, for your own piece of mind. The directions Brian gave you were correct. Once you get it starting and idling properly you can begin to adjust the mid-range (jet needle - both taper and clip position, and needle jet sizing).
Click to expand...

There is no hang if pilot mixture screwes are 3 turns out and engine does not heat up as much just by idling for 5-10 min.
Also, with smaller pilot jet, bike would not start at all, just cranks and sounds like its about to start, if quick start used it will run, but engine overheats and smells like its lean
 
Ohh and rpm doesn't hang right when I release throttle... I rev up to 6k and let go. The idle drops to 2.2 instantly, hangs there for about 5 or so seconds then goes down. As far as I'm aware, that's a lean hang
 
helloworld said:
Ohh and rpm doesn't hang right when I release throttle... I rev up to 6k and let go. The idle drops to 2.2 instantly, hangs there for about 5 or so seconds then goes down. As far as I'm aware, that's a lean hang
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Glad you sorted it out, the way I read your description could indicate many problems. Happy to hear you are on track.
 
LPakkala said:
Glad you sorted it out, the way I read your description could indicate many problems. Happy to hear you are on track.
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No.. Thank you guys! Other people throwing ideas with different opinions, that's what is figuring it out! :)

I've adjusted carbs before, but mostly top end and midrange, I never had such problems with idle circuit on any of my bikes before. And idle circuit troubleshooting guides on google are close to 0.
 
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