ST 4175 string Trimmer

[GM Guy]

Hello All.
I have a ST 4175 string trimmer that dies just off idle. I replaced the fule lines and it was running normally and then it studdered and died.
I can restart it easily but it dies as soon as I open the throttle.
Any ideas??

 

[bertsmobile1]

If the tank is full. tip 1/2 of it out .
If it will not start at all then the lines you just replaced are wrong way round

 

[GM Guy]

If the tank is full. tip 1/2 of it out .
If it will not start at all then the lines you just replaced are wrong way round

Thanks for your reply.
It will indeed start and idle with less than a full tank. It simply will not rev and dies .
The new fuel lines are clear and I can see that they’re full of fuel.

 

[bertsmobile1]

Now comes the hard bit
If it has a rotary valve carb then the check valve on the high speed circuit is probably stuck closed and that ie a fatal flaw as they can not be replaced
If you have a butterfly valve carb then the High speed circuit is out of adjustment
If it goes fluffy , blows a bit of blackish smoke then the H is too rich
If the exhaust sounds sharp the stops abruptly the H is too lean

Some times if you take the carb off but leave the fuel lines on, turn it sideways & blow compressed across the venturi a lightly stuck check valve will start to flow
You should see fuel mist blowing out the carb .

 

[GM Guy]

Now comes the hard bit
If it has a rotary valve carb then the check valve on the high speed circuit is probably stuck closed and that ie a fatal flaw as they can not be replaced
If you have a butterfly valve carb then the High speed circuit is out of adjustment
If it goes fluffy , blows a bit of blackish smoke then the H is too rich
If the exhaust sounds sharp the stops abruptly the H is too lean

Some times if you take the carb off but leave the fuel lines on, turn it sideways & blow compressed across the venturi a lightly stuck check valve will start to flow
You should see fuel mist blowing out the carb .

Thanks very much!
It has the rotary valve carb.
I suspected that it was a carburetor problem although it happened so suddenly, I had never experienced a carburetor problem like this. I’ll search for a carb kit or a new carburetor.

 

[mitchel232]

I know people use trimmers to maintain trims and hedges; however, I prefer Hedge Shears over them in order to maintain my garden.

 

[StarTech]

Walbro WYL-240-1 carburetor.

Check the metering diaphragm for stiffness, If stiff replace it.