Cleaning carb on smoking Stihl

[Khriss]

3 hours ago, spudulike said:

OK, call me a loon, a freak, a dipstick, master of the universe but.........just try winding the H screw out a couple of turns and try again. The symptoms don't strike me as being accelerator pump or check valve unless the valve is stuck shut!!

H

Yr crazy as a cokenut..... Tighten yr buttocks  ? K

[spudulike]

Damn, you found the family get together video!!!

[bmp01]

13 hours ago, spudulike said:

The only thing I would say is that drifting the check valve out is sort of simple but it is fairly unlikely to be the issue. It gives a saw a real lumpy pickup and massively over rich running - I do around 2-4 a year and isn't a common issue.

Re one way valve in main jet,

Frequency of failure dependant on carb abuse with airline.

Massively rich is coz the user tries to compensate for the broken low speed circuit by dumping in more fuel via the adjusters ?

I think it goes like this,  with factory set fuelling the saw will not run (or runs badly) at IDLE, coz some air going thro' the carb does a detour - goes wrong way up the main jet, through the metering chamber, out through the low speed jets. In the mean time the metering chamber cant do its job either.... The obvious thing to do is give it more fuel.

High speed with no adjustments all is well, but with adjustment to make low speed work it becomes rich.

Innit ?

 

Personnally once the carbs out of the saw and for the effort involved (not much) I'd be checking one way valve, if only to tick it off the list.

My money will be on the accelerator piston but thats a bit more painful to do. 

 

Title of thread was the starting point.

 

 

Edited August 8, 2020 by bmp01

[Stere]

This saw going to be like triggers broom by the time it works ?

[spudulike]

I think it is time to get this sorted - the compression and piston condition must be good to start with - if you haven't, pull the muffler off and look at the piston - a pic would be good. When you pull the saw over slowly, as the piston goes through its compression stroke, does it feel nice and spongey or is it just too easy and slack? If you lift the saw off the deck with the recoil handle, does it just tumble downwards or stick for 1-3 seconds on each compression stroke (TDC)?

If that bit is OK, it is likely that you have enough fuel for idle (low speed circuit) but not enough for high speed running (High speed circuit).

If you haven't...change the fuel filter, it DOES make a difference.

Then try the low screw on 1.5 turns and the H screw on 2 turns out. The saw should at least pickup on these settings.

If it doesn't, try H screw 3 then 4 then 5 turns out - note any differences and come back to us.

If still no joy, take the H screw out and give it a good blast of carb cleaner and reassemble L 1.5 turns and H 2 turns and try again.

If still no joy, there is a slight possibility the check valve is stuck shut - when blasting the carb cleaner down the H screw - look at the end of the check valve in the carb bore and make sure the cleaner is coming through the nozzle in to the bore of the carb (Middle bore leading in to the engine).

Worth checking the fuel line for splits - plug one end and blow down the other end - I use a Mityvac pump for this but assume you haven't got one!

If that doesn't do it, it is a real oddity!!!!

BMP - spot on on accelerator pump issues, air gets past and is then injected in to the check valve giving all sorts of idle issues BUT....high speed generally works OK and it isn't a sudden issue. A stuck pump (it happens) gives a very flat pickup but the engine will still rev out after a bit of feathering.

 

[coppicer]

13 hours ago, spudulike said:

I think it is time to get this sorted

Thanks for this spud, will study it, but got a lot of work booked for next few days, so won't be able to look at the saw again until maybe next weekend. Which is a problem, really need to get cracking on the wood now that birds are done nesting. This is the three-month window, as once we get into November/December the ground gets too wet for the Land Rover... ?

[Ratman]

Thanks for this spud, will study it, but got a lot of work booked for next few days, so won't be able to look at the saw again until maybe next weekend. Which is a problem, really need to get cracking on the wood now that birds are done nesting. This is the three-month window, as once we get into November/December the ground gets too wet for the Land Rover... [emoji51]

That’ll be your next fettling job then [emoji23]

[coppicer]

Just now, Ratman said:

That’ll be your next fettling job then

Have actually fettled the Landy a couple of times - quite successfully, to my surprise. If I had a place to work on it inside in the dry over the winter there's a few things I'd like to get done on it...

 

Was passing chainsaw shop today, found myself drawn in by some weird eddy of space-time. Apparently an MS-261 would be about £590. Must... stay... strong...

 

[spudulike]

Bloody hell, just get on with it man, sleep is for wimps, there are 24hrs in the day........failure is not an option

I was saying to the wife the other day that you forget how much knowledge you acquire over time and it is only when you tell someone how to do something you think is quite simple - fit a bar and chain for instance, you realise some know nothing and how much info you have accumulated.

 

[bmp01]

6 hours ago, spudulike said:

Bloody hell, just get on with it man, sleep is for wimps, there are 24hrs in the day........failure is not an option

I was saying to the wife the other day that you forget how much knowledge you acquire over time and it is only when you tell someone how to do something you think is quite simple - fit a bar and chain for instance, you realise some know nothing and how much info you have accumulated.

 

"you forget how much knowledge you acquire"

 

Ah, but can you remember how much knowledge you have forgotten over time ??

 

Nope, me neither.