How to adjust your Ryobi carburettor mixture screws

Having had some running issues with my own Ryobi strimmer 2 stroke engine, i thought i would create this post for others in the same predicament. In my case the engine didnt want to idle for more than a few seconds when cold and would bog down when revved, plus when warm, it didnt seem to be achieving maximium revs anymore. Its worth mentioning that before making any carburettor adjustments you should check the spark plug and regap or replace as necessary, check/replace the airfilter if fitted, any fuel filter and if fitted the spark arrestor in the exhaust, as this alone can cause poor running if it is coked up with exhaust deposits from the engine. That said it could be a poorly adjusted carburettor thats causing the clogging on the spark arrestor in the first place!

The carburettor mixture adjustment screws on the majority of Ryobi 2 stroke engines have manufacturer designed anti tamper screw heads, known as 'pacmans' because of the mouth like triangular cutout on the screws head. The necessary drivers for these screws are unavailable or extremely difficult to source from Ryobi and i was unable to get hold of any from elsewhere, so the following pictures explain how to overcome this.


I neglected to take a before picture so this first image shows the screw heads with a slot already cut into them using an open ended junior hacksaw, see the last picture for a shot of the hacksaw i mean. You will need to remove the carburettor from the engine as access is way too restricted while it is still attached, just remove the two bolts holding it onto the engine and be careful not to damage the gasket that goes between the carburettor and the engine.


You can see i have cut through the aluminium housing and into the screw heads, to make the slots so that a normal screwdriver can be used for any future adjustments. Obviously you want to get these as central as possible so go easy and dont rush. I was being careful but still managed to cut slightly off centre!



















Once the slot is deep enough, and it doesnt take much as the screws are easy to turn in small increments with very little force. Bolt the carburettor back onto the engine, remembering to use the gasket and reinstate any air filter etc.

Now start the engine and warm it up, adjust the idle screw so the engine ticks over at slightly higher revs and doesnt stall. Then while the engine idles, slowly adjust the low speed jet clockwise and/or anticlockwise until the engine runs and sounds as smooth as possible when you rev it. In the picture you can see the L stamped on the carb to identify the slow speed jet adjuster screw, this is the one on the left nearest the engine. You may have to restart the engine several times during the adjustment process.

Now hold the engine at full throttle and adjust the other screw, the fast speed jet adjuster, again until the engine runs and sounds smooth with no 'bogging down'

The engine should now idle and run/rev with no hesitation or bogging down, you will probably need to back off the idle screw a little to drop the revs back to or close to where they were before.



You can see in the above picture, with the carb back on the engine i had to adjust it by only an eighth anti clockwise for the low speed jet and a quarter turn clocwise for the high speed jet to make all the difference.


This is the open ended junior hacksaw i used, which is ideal because of the available access even with the carb off the engine and the obvious difficulty in using a normal full framed hacksaw.

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  • Just to add to this helpful article, the "pacman" adjusters can be obtained for about £5 from Amazon.

    I now have one and am going to try this procedure to fix my hard-starting Ryobi.


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