Stihl ms231 running lean

[aidank]

I have a ms231 which after you start it and pull trigger for 1 min revs up fine but tends to run lean. It roars.  Release throttle and go again and the cycle repeats 

 

High screw is turned anti clockwise all the way, doesn't make a difference if open either 

 

Any ideas 

[Stubby]

1 hour ago, aidank said:

I have a ms231 which after you start it and pull trigger for 1 min revs up fine but tends to run lean. It roars.  Release throttle and go again and the cycle repeats 

 

High screw is turned anti clockwise all the way, doesn't make a difference if open either 

 

Any ideas 

Air leak somewhere ? 

[spudulike]

Difficult to say but if it was in my hands, I would check the maximum revs and if they were higher than they should be and the high screw is turned fully anti clockwise (I am assuming limit caps are in place) then it is most likely an air leak or an issue with the fuel system. 

Generally it is easier to check out the fuel system from the fuel filter, fuel line, tank breather and carb then doing a full vac/pressure test but if the fuel system is OK then you would need to test for an air leak and be prepared to sort this out if present and then resetting the carb to correct the maximum revs.

Often you can tell an air leak is present from the effects on the low screw adjustment where you have to compensate for the extra air by richening the screws and turning down the idle screw.