One for the two stroke tuners!

[WH308]

So the other day I picked up a cheap Stihl 08s with a chain brake. I wanted a saw that would run a 20-25” bar for ringing firewood. It started well and after a clean the electric stop and chain brake work now. The saw was very smokey, but that was solved by putting some of my 50:1 fuel in it, the old fuel was very red so suspect a bit oily. The other fault it was showing was tendency for the engine speed to hunt at high revs.

I have just given the saw a new spark plug, fuel filter, fuel pipe and cleaned the air filter. I tuned the low speed jet to give me a good idle and crisp throttle response, and then using an inductive tacho tried to get the saw to rev out at 10k rpm (handbook quoted speed) despite several attempts I couldn’t get the saw to rev to 10k at full throttle only getting 8/9k and some hunting. However at 3/4 throttle it will hit 11k.
Do some carbs have an adjustable stop for WOT, and is my saw opening up too far and bogging due too big an opening of the butterfly? It’s a Tillotson HL carb.

 

[Home Loader]

Put a couple of tanks of aspen fuel through it this will give the internals a good clean. Dont use it long term as it will affect the old seals.
What colour it the spark plug? It is quite possible that you are drawing air or even struggling to draw fuel a full revs due to a blocked tank breather. The plug will tell you a lot.

 

[devonair]

Have a look in the muffler for a spark arrest screen, make sure it's clear or rip it out, first thing I do, even with a new saw
If you get stuck put a post on Arbtalk, helpful friendly bunch mostly, Spud is yer man How much work has it done? Would a slight loss of compression limit max revs?

 

[Mossypaw]

Have you tested the compression ? Take the exhaust off and check the piston, might be scored (common on Stihls)

 

[jb1]

You have got your hands on a big old beast there, i used to use one years ago, a handy tool to have and no end to its uses, you can get an attachment for a power head auger, brilliant for fencing.

 

[WH308]

To try and answer some of the questions, definitely no spark screen although I’m thinking about shoving the bottles in the muffler to burn out the oily crap from the Rich fuel.

the spark plug is shiny new, straight out of the packet. So time will tell on that front.

I suspect it’s done it’s fair share of work, but I haven’t tested the compression as I don’t have a gauge.
Would a scored piston manifest itself as a lack of rpm at full squeeze? I think I need to put the saw into some timber and see how it behaves.

 

[Nev76]

.

 

[Nev76]

We had an old 08 here and ran it on 25 to 1 mix

 

[WH308]

We had an old 08 here and ran it on 25 to 1 mix

The handbook says 50:1 for Stihl oil, 25:1 for other oils. I use Stihl 2 stroke oil.

 

[Marcher]

It's a long time since I used a saw every day, but I remember the sequence for tuning a Tillotson carb.
1. Open the slow running jet enough to get it idling a bit fast.
2. Open the fast running jet till it screams at max.
3. Turn the fast running jet back till it starts to 4 stroke {still at full throttle.) about 1/4 turn.
The extra fuel at full throttle which causes it to 4 stroke, is needed to give it the power when it is cutting.

 

[rem284]

It's a long time since I used a saw every day, but I remember the sequence for tuning a Tillotson carb.
1. Open the slow running jet enough to get it idling a bit fast.
2. Open the fast running jet till it screams at max.
3. Turn the fast running jet back till it starts to 4 stroke {still at full throttle.) about 1/4 turn.
The extra fuel at full throttle which causes it to 4 stroke, is needed to give it the power when it is cutting.

Add to that is after the fast jet has been set as above rev saw to full throtle and as above it should four stoke the cut a large log and you should hear it go from the four stroke to two stroke.

I think this 08 might be the first saw i ever used. Has it got a top handle?

 

[WH308]

Add to that is after the fast jet has been set as above rev saw to full throtle and as above it should four stoke the cut a large log and you should hear it go from the four stroke to two stroke.

I think this 08 might be the first saw i ever used. Has it got a top handle?

It certainly has a top handle.

 

[JeffreyL]

I had a problem like that, check the fuel line from tank to carb mine had split in the flexy bit outside the tank, on full chat it sucked air as suggested above. OK I see you've already done that!!

 

[rem284]

It certainly has a top handle.

Brilliant. I know the one we had didnt have a chain brake so i think it was retired

 

[WH308]

Brilliant. I know the one we had didnt have a chain brake so i think it was retired

Yeah, the 08 and 08 super’s didn’t have a brake. Mine is a later 08SEQ (electronic quick stop)

 

[WH308]

I’m going to check the tank breather pipe, maybe it’s starving it at full squeeze.

 

[sikadog]

Its running lean at top revs, air leak or fuel blockage, probably dirt in the main jet, not letting enough fuel get to the engine it needs a card clean, exept its a fuel injector.

 

[C.J]

It's a long time since I used a saw every day, but I remember the sequence for tuning a Tillotson carb.
1. Open the slow running jet enough to get it idling a bit fast.
2. Open the fast running jet till it screams at max.
3. Turn the fast running jet back till it starts to 4 stroke {still at full throttle.) about 1/4 turn.
The extra fuel at full throttle which causes it to 4 stroke, is needed to give it the power when it is cutting.

I'm wondering if the O.P's saw is 4 stroking correctly not hunting as he discribes it ?

 

[WH308]

I'm wondering if the O.P's saw is 4 stroking correctly not hunting as he discribes it ?

I’m not sure, it surges at full throttle, maybe +- 1000 rpm. It’s sufficient to make the bar buck in my hands.