Stihl bg86 running problems

[Martin]

IT has been a little while since i have posted on here, hope all had a good christmas and new year.
I'm a little stuck for ideas at the moment as to what could be wrong with a stihl bg86 I'm repairing. It starts and runs fine for a few seconds then it starts to die out and stop. It is like it is running out of fuel but when you undo the fuel cap it picks up again and will keep running when cap is replaced tightly.
I presumed it was either fuel cap or tank vent so have replaced them and still doing the same so have now replaced fuel filter and spark plug even though I know it's not spark plug.
Where would be the next best place to look for possible problem.

Thanks

 

[Automender]

I would check the spark arrestor for carbon blockage just to get that out of the way. How old is the blower?

 

[Wonkydonkey]

He probably doesn’t have a spark arrester as he in the uk like me

I’ve been thinking about this blower.. it seems odd that it starts and dies, but when you open the fuel cap it runs, and then then the cap is closed it continues to run ?

my thinking it’s carb related when cold.

have you started it from cold with the fuel cap loose ?

i have a bg56 that wants to die after starting and bogs when cold if you open the throttle a bit quick but once warn it’s fine.
I want to put a carb kit on it as it don’t prime when the bulb is pushed.
I just gotta get a kit first.

 

[Martin]

He probably doesn’t have a spark arrester as he in the uk like me

I’ve been thinking about this blower.. it seems odd that it starts and dies, but when you open the fuel cap it runs, and then then the cap is closed it continues to run ?

my thinking it’s carb related when cold.

have you started it from cold with the fuel cap loose ?

i have a bg56 that wants to die after starting and bogs when cold if you open the throttle a bit quick but once warn it’s fine.
I want to put a carb kit on it as it don’t prime when the bulb is pushed.
I just gotta get a kit first.

Yes you are right no spark arrester.
I want to think it's carb now too after doing tank vent and fuel cap as there is nothing else it could be although I may take exhaust off to make sure not coked up and piston ok.

 

[SamD]

I know this is an old thread, but I've got a LOT of experience with the BG86 blower. I'd suggest three things right off the bat in hopes it might help another that lands on this thread:

1) Spark Arrestor Screen may be clogged - these machines sometimes run a bit rich and spit a fair amount of oil out the exhaust. Clean the screen and try again.

2) Set the mixture correctly (duh).

3) If the machine still bogs down while running, twist the fuel cap counter-clockwise to open it slightly, equalizing pressure in the tank. If it does, you've likely got a breather problem. The breather for the tank is located on top of the fuel tank just to the side of the fuel cap.