LA Screw Adjustment

[oli]

I am in the process of tuning an Echo PB1000 blower with Zama C1U carb. Carb has hi, and low needle jet screws, and LA (idle) screw for throttle plate. Engine starts and runs using using preliminary adjustment of 1 1/4 turns out for hi and low jet screws. How should the LA screw be adjusted before I start fine tuning the the hi and low jet screws. Thanks in advance, Oli

[KE4AVB]

Your looking for mid point of lean and rich drop offs of the idle mixture and then same for high speed mixture. Then set idle speed, if tachometer is available, until an idle speed of 2500-3400 RPM is achieved and engine idles without stalling per owners manual.

[oli]

KE4AVB, thanks for your reply. When you indicate, "Your looking for mid point of lean and rich drop offs of the idle mixture and then same for high speed mixture", does "idle mixture" mean low speed jet screw? Does it make any difference how the LA (idle) throttle plate screw is set prior to to adjusting the hi / lo jet screws. Thanks Oli

[KE4AVB]

When it comes to most Zama carbs here I usually preset the both L and H to the will start setting of 1-1/2 turns each. Then set LA to what ever gets the unit to idle at a good speed. Then from there fine tune L for best mixture setting. LA drop to desired idle and double check the L setting afterwords. The H is the final adjustment as L interacts with it. Just have be patience while doing it this way. Sometime L has be enrich a little to eliminate most of the lag when you pull the trigger.

I would give PB-1000 carb settings but my Echo chart doesn't have it listed so have to fall on the above method. I see if Ray can find the latest chart for me but that may not be possible just depends if someone has provided him a copy.

[oli]

Thanks, KE4AVB, makes perfect sense.

[KE4AVB]

Oli,

Just receive the service info from Ray.

Here is the related info you needed. The LA setting is after the screw just touches the throttle shaft.