Stihl MS150 power loss

[Rich @ C Trees]

Morning All,

My MS150 looses revs and power at full throttle. I've changed the fuel filter, cleaned the air filter, spark plug, breather filter and stripped down the carb to clean the gauze. On rebuilding the saw and re-tuning it seems to run OK but on restarting later the same problem comes back again. It's the same fuel in all my saws so I don't think that's the problem. One other thing, there seems to be a strong smell of petrol whenever the saw is left standing in the tool shed. Could it be a leaking diaphragm?

[treedweller]

I didn't think they had any power to start with lol No seriously though you may have hit the nail on the head. If the diaphram is leaking you can fiddle with the carb all you want but it will still go out of tune. i'd bite the bullet and get it into a shop it will save headaches in the long run.

[TreeswingerPerth]

I had a very similar problem a few years ago with a husky 254 , spent ages playing with the carb only to discover the barrel scews had come loose , not that the barrel was moving , just enough to give me the running problem . Just a thought .

TS

[Daniël Bos]

Take it back, surely it's under warranty?

[woody paul]

Ms 150 not that old then, so I would go back to shop asap.

[spudulike]

Technically if the diaphragm was holed, you would get half teaspoon full of fuel out when left standing and that would be it!

 

The needle valve however, if that was leaking then if the tank had positive pressure (most do) the fuel would be pushed through the carb and run in to the engine.

 

The easy check for this is to attach a pressure gauge to the fuel pipe connector and look for leakage - it should hold pressure!

 

Has the piston been checked by removing the exhaust?

 

Other than that - the carb may need a retune if the saw is reasonably new and is running in!

 

Stihl will set the carb a tad lean to reach emmission rules but better settings that may give slow pickup when run in.

[18 stoner]

Ms 150 not that old then, so I would go back to shop asap.

 

 

To be honest, I wouldnt of even put a spanner on it:sneaky2:

[Rich @ C Trees]

Thanks everyone - good advice much appreciated. I'll give the warranty route a go first, then replace the carb which'll give me an opportunity to pull apart the current one and educate myself a little (God knows I need it!).

[Rich @ C Trees]

Firstly, my bad: it was an MS250, not a 150 as I previously stated - damn typo. Secondly, I have an answer: an incorrect carb had been fitted. The part that came off was a Zama C1Q-S87D which fits an MS210; the correct part for an MS250 is a C1Q-S85D. It's an easy mistake to make as the Stihl part numbers only differ by a single digit. However, it was fitted four months ago by someone who really should have known better so I feel a bit let down...