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Stihl Running Lean

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Hi gents it's actually my FS90 but I thought this was the best place for advice as I presume it's similar to the chainsaw engines.

 

It's done less than 50hrs use but when I came to start it the fuel bulb wouldn't fill.

 

I removed it and cleaned the black part below and it worked however now the machine won't rev cleanly and it you coax it, running at part throttle it's clearly getting hot hence I guess, running lean.

 

I then removed and cleaned the carb - which only had a tiny bit of dirt in there - still the same.

 

I'm loathe to start playing with the mixture when I suspect I haven't found the cause.

 

Are they very susceptible to air leaks - should I have used sealant on the gaskets ?

 

A search tends to find "replace carb" but it was fine and hasn't done much work.

 

Thanks

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Thanks for the reply,

 

The filter looks like new but I tried even with it removed - no change

 

The breather - I'm unsure which it is, I'll take a look but it won't rev from starting so it can't be a problem due to vacuum.

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The fuel bulbs are purges, so they pull fuel from the carb, into the bulb and dump fuel back to the tank, assuming the bulbs check valve is ok, and the hoses are connected correctly to the appropriate connection, if the bulb does not fill, it would suggest there is a fuel blockage in either the fuel filter, fuel hose, or in the carb inner screen, or metering lever too low, or inlet needle sticking.

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These machines normally have a Zama carb and they are prone to failure of the one way valve which let's fuel out of the metering chamber but should not allow air back in. When they fail the purge bulb sucks air via the valve rather than fuel. The valve is not serviceable

Best option to replace carb.

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Which makes and models have the best carbs and most reliable engines GardenKit?

 

My low hours Stihl is playing up after a winter lay off (no drive to shaft)

 

My Kawasaki (Kaaz Danarm VF500) seems ok despite the bloody Portek Rebel head being stuck on (can't replace line, can't get the bugger off!!)

 

I'm now going for the Makita 43cc MM4 model.

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Which makes and models have the best carbs and most reliable engines GardenKit?

 

My low hours Stihl is playing up after a winter lay off (no drive to shaft)

 

My Kawasaki (Kaaz Danarm VF500) seems ok despite the bloody Portek Rebel head being stuck on (can't replace line, can't get the bugger off!!)

 

I'm now going for the Makita 43cc MM4 model.

 

 

The Stihl clutch is probably just stuck if it's not been used

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