Idle mix adjustment.....

[Oobyscoot]

Does anyone know which way to turn the idle mix screw on a ZZR600D to weaken the mix. Its Kehien carbs.

Finally got this ZZR running, but its VERY rich, stone cold- no choke and still rich, revs lovely but needs the idle mix reducing a lot.

[odie]

EASY TEST to set up your mixture screws.

If at 4,000rpm; (steady state riding)
lean surging happens you need to richen the mixture (going outward 1/4 turn at a time.

A rich problem gets worse as the bike heats, lean gets better as the bike heats up.

Now to do the test: Here’s how it works (and it will get you dead spot on!)

Set your idle below 1,000 (6-700rpm works good)
1) Blip the throttle quick, lightly. If the idles rises up then drops below the set point you selected (6-700), you are too RICH, you need to go IN with your mixture screws 1/2 turn at a time.

2) If you blip the throttle and the needle rises, but then hangs for a second before dropping to the perfect set point of 6-700rpm you are too LEAN, you need more fuel, go OUT 1/2 turn at at a time with your mixture screws.

Now use your head. If you turn the mixture screws 1/2 turn one-way or the other and the problem goes back and forth from lean to rich, you need to turn less.......try 1/4 turn.

Once done, you should be able to set your idle back to normal, give a blip and have it rise fast, and drop fast right to the perfect spot. Now your mixture screws are set

If you run into problems and it just won't work. Make sure you have not intake leaks, bad exhaust leaks. Intake leaks (carbs to motor) cause the most frustration.


Also check your air filter, if its blocked it will cause a rich mixture.
Hope this helps.
Odie

[dracken1]

just to add another thing into the equasion. ensure intake valve clearance is not to tight.
the last 6 bikes i've had in have had to have thinner shims put in. i remember the days when it was always thicker ones you needed.:D

[Dougie]

Invest in a Gunson's Colourtune,it's basically a see through spark plug so you can see what the spark's doing.With a bit of experience you can get yer idle circuit bang on.

[Oobyscoot]

Odie, Cheers bud. Used your method and its running sweet now. Gave it back to its owner and told him to bring it back in a couple hundred miles and I will check the colour of the spark plugs.

Draken1, I thought I was the only one to notice this. Valve clearences always used to open up and rattle, now they always seem to go tight, why is that? When the bike first arrived with me the valves had no clearence at all, couldn't even get a 1 though feeler in there. I was tight and machined a few though off the shims insted af buying new though.

Dougie, How do they work? do they go in place of the spark plug itself? If so the plugs are about 8 inches into the engine, I wouldn't be able to see it.

[Borg]

Colour tune are shit