MS650 idles fishy. Need help!

[Wood Doctor]

From the 650 service manual.

 

[popopboat]

Anything extraordinary here?

 

[popopboat]

View attachment 278361From the 650 service manual.

Thanks for quick response, but unfortunately, that is exactly what i did.

 

[huskihl]

Is the L screw turned in far enough? What does it do if you turn the L screw in a quarter turn and back off the idle screw?

 

[popopboat]

LA screw has to be all the way out with 1 turn out on the L, otherwise chain spins.
tacho is on the way, but im pretty sure rpm is around 2500
Turning L while idling makes a difference, so nothing is "stuck", and rpm doesnt change, check valve should be working

I was literally throwing saw in every single rotation and rpm doesnt change at all.
4 stroking when richened is a no problem, so im very-very sure no air leaks.

Is that hole on a valve plate maybe too big? so too much air goes through?

 

[huskihl]

LA screw has to be all the way out with 1 turn out on the L, otherwise chain spins.
tacho is on the way, but im pretty sure rpm is around 2500
Turning L while idling makes a difference, so nothing is "stuck", and rpm doesnt change, check valve should be working

I was literally throwing saw in every single rotation and rpm doesnt change at all.
4 stroking when richened is a no problem, so im very-very sure no air leaks.

Is that hole on a valve plate maybe too big? so too much air goes through?

If the idle screw has to be all the way out or the chain spins, you either have a bad clutch drum bearing, bad clutch springs, or your throttle plate is not closing all the way. If you’re sure the first two are OK, I would loosen the throttle plate and snap the mechanism shut a few times and re-tighten the screw. Or you still have a small air leak

 

[popopboat]

Bearing is fine,
springs should be fine, (but i might replace them anyway) . I think chain spins because rpm is getting too high and not because of weak springs, but ill check at which rpm does clutch engage when tacho arrives.
Tried snapping throttle plate multiple times, no difference.

I mean, one full turn out on the L is really a spot on adjustment with the LA all the way out.

Any ideas how to check for an air leak without the equipment?
Ill try maybe squeezing intake boot to see if it gets any leaner.

 

[BangBang77]

Rotating the saw while idling can help identify a crank seal leak as you are probably aware.

You can also lay the bar against something and while holding both handles, with the saw idling, manually flex the crankcase in the AV on all sides can sometimes help identify a torn boot or impulse line.

 

[huskihl]

Tried snapping throttle plate multiple times, no difference.

Did you loosen the screw? If the butterfly isn’t centered perfectly in the bore with the tapered edges sitting the right way, it won’t shut completely and would cause your symptoms

 

[popopboat]

Did you loosen the screw? If the butterfly isn’t centered perfectly in the bore with the tapered edges sitting the right way, it won’t shut completely and would cause your symptoms

Yep, barely any light comes through from a flashlight.

Edit: ive also tried spraying wd40 around airleak potential zones and on oil seals, no change in the rpm.

 

[Lee H]

Who ever loosened the butterfly screw needs a new screw driver. Someone
has been in there. I'm not familiar with those carbs but is the butterfly suppose
to have the notch where the hole is in the body. I have seen modded carbs
with that.

And as huskihl says the butterfly needs to be set correctly or it won't close

 

[huskihl]

Anything extraordinary here?
View attachment 278367 View attachment 278368

The butterfly needs rotated about 2-3° counter clockwise. Look at the alignment marks

 

[kneedeepinsaws]

View attachment 278361From the 650 service manual.

This took me forever to understand, and i may still not understand,
The stock L jet setting is fundamental in determining the idle screw. If the idle screw is open too much and the L jet is adjusted to match it you start to use fuel from the main jet at idle causing problems with idle and WOT returning to idle problems.
From my experience you really should only be adjusting the L jet half a turn at the most more than stock.

I had one saw that was having trouble returning to idle after WOT and the L jet was like 3 turns out and the idle screw was quite a ways in.

Im not as experienced as some others here so I would appreciate any corrections to this as I may still not fully grasp this..

 

[Vintage Engine Repairs]

1&1 on screws
Adjust La for smooth +/- 200rpm within spec idle
Let warm up for a couple mins with varying throttle
Turn L in and out until it runs fastest
Richen L just slightly until it’s no longer lean (you may have to adjust La for each L adjustment)
Alternatively bring the LA up to where the chain just starts to move and then find lean drop, richen it for smooth idle and lower La after. Either / or, makes no difference. Mostly it’s down to the saw and La travel.

Check acceleration


If it burbles or splutters - lean L
If it dips / bogs / delayed - Richen L

Don’t chase your tail, close is good enough for now..

Adjust La to maintain idle spec.


Go WOT and set to 500 rpm below spec.


Now stick it in the wood and get the saw hot. Tweak as necessary for 4 stroking as soon as the slightest pressure is lifted off the saw, but clears up under full load.

Tweak L and La as necessary for smooth off idle acceleration.

 

[popopboat]

Alright, been fidgeting with this and it just wont change.
According to microphone "tacho", idles at 2800 ripms.

I mean, i doesnt bog,die or anything "serious" just has a slight acceleration delay. And it happens only after a bit of cutting, then clears up after half a minute or so of idling.
I think ill stop chasing my tail now.

Ive made a sound recording, so if you are willing, have a listen.

 

[huskihl]

Clutch drum, bearing, springs, or the clutch itself is rattling pretty good. Might be causing the chain to spin a little for as low as it’s idling

 

[popopboat]

I might wrongly explained, now it idles at 2800 rpm +-50 and chain doesnt spin. (atleast not anymore)
According to stihl, clutch engages at 3000rpm, so clutch should be fine.

EDIT : I think microphone also enhanced the rattle, its not that bad in first person

Thanks everyone!

 

[Wonkydonkey]

That sounds like my 036 ticking over. A bit of ting ting ting... what I’ve thought is the crank is a bit worn ( 1996 crank) and the bearing wobbles on the crank thus the cluch drum does ting ting ting on the break band.
When on tick over just get a small screwdriver, ie the one for adjusting carbs.. stick it somewhere (where the sun don’t shine) ie to stop the brake band going ting. I found just pushing it and not touching the drum convinced me it was the very slightly warn crankshaft


See if it works for you

 

[popopboat]

Im speechless....
Luckily appears like its just a worn ball bearing

 

[popopboat]

It is!
Thank God...




Clutch came loose 2 times, my stupid angry arse decided that threadlocker would fix it .... Cant fix stupid.



Luckily! Piston was ready to go 10 cords ago, was too impatient to order a new one.
Slap glazed cylinder a bit, but nothing severe.



In the end, poor bastard already paid itself over 3 times, finished annual firewood batch.
I think it does deserve a new piston and bearings.


EDIT : Thank you @Wonkydonkey, I wouldnt really bother checking without your "reminder".