Tuning issues stihl 066 fresh top end

[scottw99]

Hello, first post here. Info to get started:

Stihl 066 red light converted to unlimited coil with proper flywheel.

I purchased the saw with a damaged piston, cylinder was in okay shape. Seller gave a piston kit with it, I installed said piston kit. Installed new seals and pressure/vac tested it, installed new fuel line, fuel filter, impulse line, intake boot, carb kit, spark plug. Fresh 91oct with 32:1 Bel-ray H1R.

It's starting and idling just fine, but I can't get it to four stroke at WOT - worried about it running lean. The new AM impulse line doesn't seem to be sealing super tight against the bottom carb nipple so I pulled a bit more through the hole and the issue is still there.

Seems like it's running lean, or not getting enough fuel delivered, any ideas? I turn the H needle out fully and it dies before it will four stroke at WOT.

 

[jb-chainsaws]

It does sound a bit suspect, but how's your ear with regard to four stoking? By that I mean what experience do you have with this?

Best suggestion would be to get yourself a tach, if it's running a few grand over what it should be no matter what you do to the needle it has an air leak. I suspect this will be the case with your description so best not to run it til it's sorted.

How did you perform your pressure/vac test? Talk us through it to make sure you haven't missed anything. Personally I'd always use genuine impulse lines, and the intake boot doesn't normally need changing unless it's gone stiff or has a split. Check you havent tightened it too much into the cylinder as this can tear the poorer quality aftermarket boots if that's what it is.

Let us know how you get on

Edit: and welcome! There's some awesome people on here with a vast wealth of knowledge, it's always nice to see new people joining

 

[scottw99]

Thanks for the quick reply. I've tuned 3 different saws now using a variety of different fuels so I feel comfortable identifying the four stroke and getting it running at a nice point by ear.

I don't have access to a tach right now, currently checking out to see if any apps are worthwhile for acoustic tuning.

I pressure tested only the bare cylinder after installing the new seals, so I guess I haven't tested the intake side fully. I was using a mityvac hooked onto the impulse nipple with the intake/exhaust blocked, it held vac and pressure at about 7psi.

I'll do some more extensive pressure testing since it does seem like an air leak to me too, I didn't want it to be that though I thought she was buttoned up nicely.

Thanks, I've been bitten by the chainsaw bug. I have four saws now and one of those farmertec ms660 kits coming in the mail, I saw this 066 redlight on a local ad site with a blown piston and replacement included and I couldn't resist!

It does sound a bit suspect, but how's your ear with regard to four stoking? By that I mean what experience do you have with this?

Best suggestion would be to get yourself a tach, if it's running a few grand over what it should be no matter what you do to the needle it has an air leak. I suspect this will be the case with your description so best not to run it til it's sorted.

How did you perform your pressure/vac test? Talk us through it to make sure you haven't missed anything. Personally I'd always use genuine impulse lines, and the intake boot doesn't normally need changing unless it's gone stiff or has a split. Check you havent tightened it too much into the cylinder as this can tear the poorer quality aftermarket boots if that's what it is.

Let us know how you get on

Edit: and welcome! There's some awesome people on here with a vast wealth of knowledge, it's always nice to see new people joining

 

[scottw99]

Seems like there is a small leak on one of the seals, I tested it right after installing them and it held vac but now it isn't. Thoughts? Do I have to redo them?

Thanks for the quick reply. I've tuned 3 different saws now using a variety of different fuels so I feel comfortable identifying the four stroke and getting it running at a nice point by ear.

I don't have access to a tach right now, currently checking out to see if any apps are worthwhile for acoustic tuning.

I pressure tested only the bare cylinder after installing the new seals, so I guess I haven't tested the intake side fully. I was using a mityvac hooked onto the impulse nipple with the intake/exhaust blocked, it held vac and pressure at about 7psi.

I'll do some more extensive pressure testing since it does seem like an air leak to me too, I didn't want it to be that though I thought she was buttoned up nicely.

Thanks, I've been bitten by the chainsaw bug. I have four saws now and one of those farmertec ms660 kits coming in the mail, I saw this 066 redlight on a local ad site with a blown piston and replacement included and I couldn't resist!

 

[Redfin]

Did you clean the carb? Inlet screen clear?

 

[scottw99]

Carb is clean and screen is good. I'm fairly certain the new flywheel side seal I put in is leaking, but it's very slow I think I can faintly hear it. I guess I try to replace it again??

 

[jb-chainsaws]

redo that seal and make sure it's holding both pressure and vac as the crank is turned. also ideally see if you can get one of the still special tools for pressure and vac testing, I forget the part number but google should help. I think its called something like a pressure test manifold. but that way you can block off the exhaust and test the whole intake and impulse system too

 

[scottw99]

I can't confirm the leak now, no bubbles from either seal, I think my block offs are not holding maybe? My brain hurts

redo that seal and make sure it's holding both pressure and vac as the crank is turned. also ideally see if you can get one of the still special tools for pressure and vac testing, I forget the part number but google should help. I think its called something like a pressure test manifold. but that way you can block off the exhaust and test the whole intake and impulse system too

 

[Glock37]

When u install fly wheel side seal coat outside of seal with 518 and make sure its about 3/16 in below flush
Maybe this will help give 24 hrs before pressure after installing seal with sealer


Sent from my iPhone using Tapatalk

 

[scottw99]

I've confirmed the seals are alright, my block off ports were not sufficient and also I think the spark plug tightness came into play (one round of the bottom thread was loose when I got the saw, I snipped it off, ground it flush, and tapped it, maybe it has reduced sealing from the missing thread?)

With bare cylinder/saw, intake blocked, exhaust blocked, mityvac on the impulse it held vac and pressure around 10psi.

Just buttoned it all back up again and same symptoms. I haven't been able to tach it yet, so my next assumption is it's not getting enough fuel to 4 stroke? I still need to test the impulse line back but I don't think there is an air leak...

 

[scottw99]

If it was an air leak wouldn't I be able to turn the high way out? Maybe a missing piece of info here is that the saw is dying out at the top end between 1.5 and 2 turns out on the H screw.

EDIT: Pulled the metering lever up a bit, it was a bit low. I'll have to wait until tomorrow to do some more tuning/testing.

Also thoughts on the tank vent? Anything I should be looking out for there? Maybe it's not sucking enough fuel at WOT.

 

[bikemike]

Bet s carb kit is needed remove Welch plugs and make shure all those are clean.
Sometimes the simplest little thing is the biggest mind *f-word

 

[bikemike]

Oh yeah. Does it have a spark screen?

 

[scottw99]

Oh yeah. Does it have a spark screen?

I'll check the welch plugs, I took the spark arrestor out already

 

[huskihl]

Make sure your carb gaskets are in the right order. On the one that pushes on the needle, the gasket goes to the carb. On the opposite side, the diaphragm goes to the carb

 

[bikemike]

Make sure your carb gaskets are in the right order. On the one that pushes on the needle, the gasket goes to the carb. On the opposite side, the diaphragm goes to the carb

I did that on my echo top handle a few days back. I knew what I've done when it would flood while shut off

 

[scottw99]

Air leak is at the spark plug. It's holding vac and pressure with the old plug torqued tight with anti size on it. I'll have to put a helicoil in it. The thread was hanging loose at the bottom when I got the saw I snipped it off and ground it flush. I guess that extra bit makes a big difference.

This setup is with rubber over the intake boot with the carb bolted on, and one behind the exhaust so the whole system is now tested

 

[huskihl]

Don't think that's enough of an air leak to cause your symptoms. But maybe

 

[scottw99]

Don't think that's enough of an air leak to cause your symptoms. But maybe

Well I'm glad to say it was the only air leak on the saw. There could be other issues but the air leak would certainly contribute. Also consider that while running an air leak directly at the top of the combustion chamber could be amplified greatly.

With the spark leak as is, it would drain out 10 Psi over about a minute.

 

[Canadian farm boy]

Have you replaced the fuel filter? Is the fuel line soft? The fuel line could be collapsing