How do I get my Ryobi to run without choking about 1/4 choke? I've taken the carburetor completely apart, and cleaned the same with carburetor cleaner, and it still runs exactly the same. I have to run it at 1/4 to 1/2 choke. Will not run at all with choke completely off. Primer ball is good, fuel lines new.
This is a Ryobi 875r 4 cycle string trimmer, straight shaft.

Sam, September 2009

RE: Johns answer...

It should be noted that Sam has a 4 cycle engine here (like the lawn mower), not a 2 cycle, so there won't be any diaphragms in the carb, just throttle/speed jets, speed adj screws and standard mini venturi section.

Dave, September 2009

Need to set the idle and hi speed screws to factory spec. It runs when partially choked because you are running it RICH, which will damage the engine soon, as well as deposit large amounts of carbon up in the head/piston area, which will cause knocking/detonation eventually.

Idle speed is set with the throttle at low, intitial setting is 1 1/2 turns out from lightly seated. Adjust out until the engine begins to slow or miss, turn in until the tach indicates 1400-1450 rpm (borrow or buy an inductive tachometer from Harbor Freight).

High speed is most likely just a stop for the throttle plate, set throttle to high, and adjust the high speed screw till you read 3600 rpm.

Dave, September 2009

If you are happy that the carb is perfectly clean, you'll need to replace the rubber diaphragms inside the carb to restore performance. Just make sure you look where everything goes!

John, September 2009