Stihl fs 300

[darroch]

Hi guys

I picked up a good machine that needed a new carb( non starter)

Got a cheap new carb and machine starts up fine with good power. Set the carb up on a decent YT channel guide .  Problem is that when hot, it dosen’t like idle. It gassed up and stalls at idle, then will not start again till motor has cooled. 

 It will use the full tank of fuel if you keep it at high revs. E5 premium fuel

[ChrisNewport]

Remove the exhaust and check the condition of the piston through the exhaust port. Typical symptoms of a knackered top end.

[Stubby]

6 hours ago, darroch said:

Hi guys

I picked up a good machine that needed a new carb( non starter)

Got a cheap new carb and machine starts up fine with good power. Set the carb up on a decent YT channel guide .  Problem is that when hot, it dosen’t like idle. It gassed up and stalls at idle, then will not start again till motor has cooled. 

 It will use the full tank of fuel if you keep it at high revs. E5 premium fuel

Sounds like low comp . Once it gets hot and parts expand the compression drops off to the extent it wont support combustion . The other simple thing is it could be a blocked tank vent pulling a vacuum . See if it will keep running with the tank cap off .

Edited August 12, 2022 by Stubby

[spudulike]

The coil may be a bit off, worth checking the gap as coils tend to stop sparking when the gap is a bit big and the coil warms up.

[darroch]

These are the things going through my mind guys  My comp readings were a bit lower than spec and the head looks a bit oily after a hard hour running. I will check these things out and see if I can use the vac gauge I bought to test crank seals etc.  I will check coil gap and clean then report back

 

[darroch]

2 hours ago, ChrisNewport said:

Remove the exhaust and check the condition of the piston through the exhaust port. Typical symptoms of a knackered top end.

I did that Chris. What I could see there was no scoring on cylinder or piston. Not to say rings may be worn though?