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Carburetor adjustment on McCulloch Mini-Mac 30

Which way does one turn the idle adjustment and high speed adjustment needles to increase or decease speed/power? The manual does not say.

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Turning Hi & Lo mixture screws in leans the mixture,out rich-ens it.turn the T screw in to increase idle speed the chain should slowly come to a stop at idle [chain brake off] adjust Low needle first until it accelerates smoothly then Hi needle for best 'revs'.then Lo again if necessary if you don't know where they were set before,start w/ screws 3/4 to 1 turn out from a lightly seated position

Posted on Sep 23, 2009

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You got it almost right. The screws go in to lean and out to richen. Idle will be in to increase and out to lower.
Always adjust the high speed needle first. Slowly lean till you hit top rpm then back off 1/8th turn.
Low speed needle, slowly lean till the engine stops burbling on exceleration. If you go too far the engine will stop quickly when the throttle is advanced. Back it off a little and try it again.
Back to the high speed needle, adjust again.
NOW adjust the idle screw.
Time to adjust the needles again.
This procedure may need to be repeated as the engine breaks in. Most small industrial engines need a minimum of 5 gals through the engine to break in.

Posted on Feb 12, 2010

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1 Answer

What is the initial carburettor adjustment for a mac 120 MCCulloch chainsaw?

Hi williamsc32...
Before you remove or try to adjust your low and high speed jets you should always count the number of turns it takes to lightly seat the idle mixture screw and high speed needle adjusting screws.
Be sure to write the number of turns down on a piece of paper so you will know how many turns from the seated position to open the jets when you go to reinstall them, or if you remove them for cleaning or replacement.
If you have aready tried to adjust them then the adjustments below should get it running for you for final adjustment when warm.
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Then you will re-adjust the low speed of the engine when the engine is warm by turning the idle screw in or out till the engine runs smoothly at idle speed, around 1200 RPM.
The high speed jet is adjusted to 1 1/2- 1 3/4 open from the bottom seated position, after the engine is warm.
Then re-adjusted by turning the High Speed jet adjustment screw in or out till the motor runs smoothly at high speed.
Alway use the "lightly seated" method if you have not changed the screw settings.
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1 Answer

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You should have what's called a 2 needle carburetor. A larger screw adjustment for idle, and a smaller for high speed.

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