MS650 idles fishy. Need help!

[popopboat]

Hi,
basically my ms650 that i repaired acts real fishy.

Starts flawlessly, idles nicely, runs steadily and without any fluctuations in rpm and/or sound, BUT
tends to die after WOT, or simply pressing and releasing the throttle quickly.
RPMs go down to almost dying and/or sometimes slowly dies, but if i hold the throttle and release it slowly that does not happen.

It does not increase rpm by itself and does not spin the chain, carburetor settings are : bit less than 1 turn H, 1 1/2 turn L, nothing unusual to compensate for air leak, therefore id remove air leak suspicion.

I had those symptoms with bad nozzle check valve, this one works BUT i found out that there is an aditional hole parallel witht the main nozzle, doesnt that kill the purpose of the check valve?!
Also checked carb on my 064, has the same additional hole.

The one on the picture bellow.


Membranes are fine, diaphragm looks good, does not bind or anything.

Im running out of ideas, anyone has still some left?

 

[huskihl]

Tuned too rich on either the h or l screw

 

[Wood Doctor]

Tuned too rich on either the h or l screw

I tend to agree primarily because I ran into this with my Husky 353 last week. I closed the H screw a quarter turn and that solved it. Bumping up the idle did not solve it.

 

[Stump Shot]

Yup, tune is out of sync.

 

[Wonkydonkey]

I,d say a combination of both. Ie, but not your prob, it was what I found out on one of my saws.

the low was rich and the high was lean. It would tick over as yours does, but with a bit of more high and less low and a jiggle of the LA I got it there. By slowly adjusting each and testing all the way..

 

[popopboat]

Thanks to all of you for the answers.
I actually had a spare diaphragm to replace then fidgeted with the carb for like half an hour but unfortunately only partially solved the problem. Now it doesnt immidiately run fishy, only after a cut, before it ran that way right after the cold start.

L is leaned so much that it barelly runs stable on the idle, leaned H so it almost cant four stroke, but bastard still tends to die, im sure it dies because of too rich mixture as it smokes and is really sluggish on the throttle.

Other than that i removed baffle and i can say that i have a new saw lol.
Starts first pull with choke, then first pull without choke, everything is spot on, but for some reason it doesnt like me :S

PS. LA screw can be all the way out without any problems, i checked butterfly valve plate and it sits and closes perfectly.
??

 

[popopboat]

Ok i made a mistake about that additional hole, i cant suck air through that thing, check valve closes completely, no leakage.
I guess ill have to lean H a bit more, hopefuly i wont end up with piston mark on my forehead.

But still LA fully closed bothers me a bit.

 

[Stump Shot]

Ok i made a mistake about that additional hole, i cant suck air through that thing, check valve closes completely, no leakage.
I guess ill have to lean H a bit more, hopefuly i wont end up with piston mark on my forehead.

But still LA fully closed bothers me a bit.

Get the L and LA set right first. Going to need the throttle plate cracked a hair and the L richened. Usually this works itself out when the L screw is tuned right then the LA to set idle speed. Do this with a warm engine, as a cold one can skew the results. Then set your H the very last thing as it will change slightly with L adjustments.

 

[popopboat]

Thanks, will give another shot tommorow.
Hopefuly im missing something, because that is pretty much already my adjusting procedure.

Why the hell are 660/650s so delicate?? are other stihls too? i mean, my 359 eats as much fuel as i want lol, its really forgiving.

 

[popopboat]

One more question: can anyone tell if 660 carb has a check valve only on the main jet or on the idle jet also?

 

[Stump Shot]

One more question: can anyone tell if 660 carb has a check valve only on the main jet or on the idle jet also?

The idle circuit is just a series of holes usually about three or so in the carburetor body and activate as the butterfly valve opens and passes by them one by one. On the inside they are located underneath the welch plug, it has to be removed to access them. If you take the L screw out and put the plastic nozzle in of carb cleaner spray you can get a visual of these being open or not. An acupuncture needle works good to clear them out if the get plugged.

 

[drf256]

Id pressure test the carb too. Hook pressure up to the fuel inlet on your carb and see if it holds at least 15psi.

A leaky needle and seat will allow fuel to ooze from the main jet at idle and puddle, causing all sorts of wacky issues. It’s an easy check.

Like Steve said above, those 3 holes are idle and transition holes. They enter the carb bore from the wet side through the Welch plug area. You won’t see their entry in the metering area unless you pull the plug. Don’t think you need to pull the plug, just use carb cleaner (wear safety glasses) like Steve said through the L needle hole.

 

[popopboat]

Idle check valve wasnt working on WJ69 , or was contionuously stucking, spent like half a can of carb cleaner in hope to clean/unstuck, and eventually gave up, now quest for one begins ( anyone knows where? )
Replaced needle valve on the 064 carb and now 064 is in use. Identical "symptoms" occured without adjusting even with this carb.

Will do a needle test but what are the odds that both carbs are failing, for now it seems to be working, i leaned the H far beyond my comfort-zone, but it still barely 4-strokes at no load so i guess im fine.
It definitely had something to do with H adjustments, because if i richen H any more, it dies.

Can anyone still tell me why is there parallel hole with main jet which doesnt have a check valve? (connected with "screw-like?" nozzle)

Goddamn fancy Stihl.
Thanks everyone.

EDIT: Found few threads with these symptoms, and everyone "fixed" by leaning H, i suppose thats it.

 

[Funky sawman]

When I worked at a Stihl dealer, they had hundreds of wj67 and 69 carbs in the scrap iron pile. Almost all them had new kits installed, but obviously didn't work. I stole some lol and managed to get one out of 3 working with a new main nozzle check valve.. those main nozzles are real problem child's, that's why I like the old hs228 like on husky 288, they are stupid simple, just a screen defuser in those

 

[popopboat]

Hah, wouldnt really call that "stealing", tbh id do the same thing.
What were the symptoms on these carbs if you remember?

 

[Funky sawman]

You could set the carb, then rev it once, then it would lean out or go rich, chasing your tail so to speak. Stihl tech support actually told us to just replace carbs. By time you buy a carb kit which was 20 bucks and main nozzle which was 17 bucks at dealer, then labor to install said parts at 90 an hr minimum labor charge, you are better of swapping the carb for a new one

 

[popopboat]

Alright.
Yesterday i pressure checked carb and metering valve was pretty good but still i tried to improve it.
I took a valve seat out, polished a bit, put a needle valve in a drill chuck to "lap" it a bit.
Tried streching lever spring a bit to ensure better sealing.
Put everything back in, adjusted the lever just so needle valve barely opens.

Today made a test, minisclue improvement.
Then i said fck it, will try to fix last thing i suspect, if it doesnt work, ill just leave it as it is.

Soldered shut the threaded nozzle, drilled a 0.5 mm hole instead of original 0.64 mm , and IT REALLY SEEMS TO WORK, now i can richen it far more into the four-stroke zone and it doesnt bog down.
I think i did it, dangit!

Hopefuly this is not just a false alarm.

 

[popopboat]

Hell yeah!
Did some continuous cutting for cca half an hour and it never tried to bog down!
Hovewer it tends to idle a bit leany for a few seconds after startup. How "normal" is that.

 

[huskihl]

Normal

 

[popopboat]

Alright, fugger still doesnt run right (according to my littleness)
I mean, bastard runs absolutely normal, doesnt bog or lack power, nor dies or anything else abnormal after WOT, BUT ! after idling for like 10 seconds or so it goes into a "Limp" mode
Appears like it starts sucking excessive fuel, and is really slow on first acceleration after that "longer" idle. afterwards acceleration is pretty much instant.
Cant lean L anymore without spinning the chain and H is on the edge of fourstroking at no load.

Can anyone tell me their settings on the 650 or 064? Nothing else crosses my mind anymore...
p.s. no air leaks and ive replaced nozzle with an original one