HS 85 bogs when revving

[ipbr21054]

Ive been using this all ok but today when i tried to start it i wasnt able to rev it without it bogging then stalling.
I only used it say 6 times & filters / plug / fuel are all new.
Carb was also cleaned

Where should i be starting to have it running like it should.

 

[lostinthelight]

Stihl HS 85 user manual (English - 62 pages)

Manual Stihl HS 85. View the Stihl HS 85 manual for free or ask your question to other Stihl HS 85 owners.

www.manuals.co.uk

 

[ipbr21054]

Thanks but didnt help me out.
Ive taken the carb off & cleaned it out but it was ok anyway.
I managed to get it to start & run to a fashion enough to cut the hedg, this was only with choke 1/2 on all the time.

Ive now ordered a carb with 3 adjustment screws to give me more control as the carb fitted only has 1 screw of which now doesnt really do anything other than allow the item to stall when touched

 

[Burnerman]

If the machine worked better with some choke then there has to be some degree of fuel starvation.
This is due to either a partial blockage - maybe in the tiny filter just above the needle valve - or some deterioration in the pump or metering diaphragms.
You’ll rarely see carburettor faults, and it takes an experienced eye to tell if the diaphragms are likely to give problems.
John

 

[ipbr21054]

Im sure that the carb isnt blocked as used carb cleaner & a lot of it.
The diaphragm which has the metal part attached seemed flimsy.
This part is the one that is sat on top of where i undo the phillips screw & check viton needle tip & has that slim bar holding down the spring.

I agree its starved but the only screw when touched dont realy do anything so i order a carb

 

[Burnerman]

The diaphragm you are referring to is the metering one, the pump one is at the other end and has two U shaped flaps.
The needle valve lever, operated by the metering diaphragm needs to be parallel with the carb face.
The gauze filter - often blown away without people noticing - is directly below the needle valve tip.
Just a few points for info!
John

 

[ipbr21054]

New Chinese carb arrived & fitted.
Second pull of the rope & started.
I’ve let it warm up & then grabbed the throttle lever. Adjusted the H screw so it’s now running great at full throttle.

The other 2 screws are ticker over LA screw & running screw at idle L screw.

How should I be adjusting these & in which order.
I ask as I see the blades slightly operating at tickover & think this isn’t right.

 

[Burnerman]

Turning the L screw clockwise weakens the mixture and the machine should speed up a little.....although it won’t have any power to accelerate.
Turn the L screw anti-clockwise richens the mixture so do this until the engine starts to slow down, then clockwise again to the position where the engine is about to slow down - if you get my drift!
The engine should accelerate well here as it’s getting plenty of fuel.
Adjust LA screw so the blades are just not moving.
John

 

[ipbr21054]

Ok
Job when dry thanks.

 

[Harry Bloomfield]

I managed to get it to start & run to a fashion enough to cut the hedg, this was only with choke 1/2 on all the time.

That suggests the cause to be fuel starvation, not enough fuel being supplied to the engine/ weak mixture.

 

[ipbr21054]

Changed carb and running much much better.

 

[oldbutnotdead]

If you're not using the thing all that often, run it on the good fuel (my garden tools all get Shell Vpower out of the bikes). There's a link in here somewhere to some pukka garden fuel.....