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MS361 dies when closing throttle

Started by Bradford8385, February 05, 2019, 08:31:46 PM

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Bradford8385

Hello, I'm new to the forum and new to working on chainsaws. 
My ms361 has ran great for me and never have had a problem but a few weeks ago I was getting firewood and it died on me. It will start if I give it throttle but as soon as I close it it dies. No sputtering or spitting, just dead. I put a carb rebuild kit on it, fuel line and filter, but same issue. Impulse line looks like new. Carb was practically spotless when I took apart.
 If someone could tell me how to do any tests to narrow it down I would be eternally grateful.  all I really have is a vacuum pump/gauge. Have automotive tools and test equipment but none I think would apply.
Any help would be greatly appreciated. 

Tom King

Have you ever cleaned the screen in the muffler?

sawguy21

Is the idle speed set just below where the chain starts turning?
old age and treachery will always overcome youth and enthusiasm

Bradford8385

Muffler screen was spotless. 

As far as idle speed I've never even touched any of the adjustments on carb before this happened and it always ran great, no problems. One minute it was fine and the next it wasn't. 
 How can I set the idle speed without it being able to idle? I dont see how that's possible but I've been wrong more times than not lol. 

Bradford8385

But to clarify I did try adjusting but no matter what when throttle is released it dies. 
At first I thought it was inlet needle because it had an ocular groove in it and figured it wasn't seating or something. I've had this thing apart so many times I'm about to do the unthinkable and take it in to the shop and pay someone to figure it out. 

welderskelter

If it dies when released then the idle part of the carb is plugged somewhere.Take it apart and blow out the carb. Esp in the hole where the idle adjustment is. Be sure to count how far it is screwed out before removing. Watch so you dont blow out the little brass outfit in middle of carb. Might be a good idea to hold it down in a 5 gal. bucket for that. Good luck.

Air Lad

To die on deceleration could be caused by quite a few things
Some causes can be 
metering lever too low
low adjustment blocked /dirty
main nozzle check valve issue
When doing the carb kit did you remove adjustment screws and spray with carb cleaner (with safety glasses on) ?
These things can do you're head in if you don't have good patience
All the best with it mate

ladylake

 
 To increase the idle speed turn the screw marked T in some, clockwise.  If you clutch is hanging up that will make it kill also.  Try taking the bar and chain off and see if it idles.   Steve
Timberking B20  18000  hours +  Case75xt grapple + forks+8" snow bucket + dirt bucket   770 Oliver   Lots(too many) of chainsaws, Like the Echo saws and the Stihl and Husky     W5  Case loader   1  trailers  Wright sharpener     Suffolk  setter Volvo MCT125c skid loader

Bradford8385

I know how to adjust the idle but it doesn't help. I sprayed carb cleaner through entire carb when I had it apart. And air. Metering level is flush with top of carb. I thought it might have been to high because it was higher than flush so I put it down to where a razor blade dragged across just barely touches it. Still no change. I don't have a metering level gauge but the repair manual for my saw just says to make sure it's flush. 

Bradford8385

Bar and chain haven't been on it since the day I started trying to figure out the problem.
What are symptoms of a faulty tank vent? Could that cause my problem?

Wait, "screw marked T"  ?????  I have the high and low and throttle stop screw. H, L, and LA.
 I didn't take out the throttle stop screw when I cleaned carb, should I have? 

joe_indi

Is the exhaust looking oily? Is the spark plug deposit black and wet? If the carb seems fine, there are a couple of other possibilities.

A portion of the piston between the two rings is missing (verifiable by removing the muffler)

The flywheel key is sheared causing a change in ignition timing (You will need to remove the flywheel to check this)

The HT ignition lead has lost its insulation and is throwing sparks (Run it without the top cover in a dark place to check)

The choke butterfly is not opening fully (Run it without the air filter)

The pump diaphragm might have a leak (If you dont have a pressure gauge just replace it)


Bradford8385

Thank you joe! These are mostly things I haven't gone through a hundred times already, exactly what I needed. I appreciate it. 

Not sure what you mean by exhaust looking oily. The muffler or actual vapor ? lol I'm not trying to be a smart ass, just trying to understand exactly so I can figure this out. Lol

I did pull the plug and it was wet and blackish but it was after I'd been messing with it. I'll start it like normal and post back tomorrow. 

The piston might be missing something!? That sounds awful and where would it go without damaging anything else. I Will pull muffler and post back on that too but I sure hope that's not it. 

Flywheel key...will also check out and report back. 

Ignition lead.... funny you should mention that. This all started shortly after I replaced ignition lead and plug boot on. The only thing I did differently than the manual said to was I didn't pack the ignition module with the special grease it says to. Mainly because I don't have any and didn't want to substitute something and screw it up. I convinced myself that the problem wasn't related and just coincidence because it ran fine for about a bed full of firewood after ignition lead replacement. And I figured timing would effect more than just my idle but I don't know much on the subject. I will check this out as well. 

Choke butterfly- i would think that would cause it to sputter spit or run poorly but will verify this as well

Pump diaphragm- I put a new one in with carb rebuild. That's listed on the walbur troubleshooting chart as possible cause so I'm pretty sure I've been over that one making sure everything was in order. 

I have a vacuum gauge/ pump. Any tests I can do with that? Like tank/ tank vent/ fuel line, etc? Also have several fuel injection tester gauges and hoses and whatnot. 

Thanks again, you've given me some clues to work with. I hope you check back to see what I came up with. 


joe_indi

'Exhaust looking oily'  what I intended to ask was whether the exhaust exit looks oily, an indication of too much fuel, insufficient compression, poor combustion, intermittent ignition, or even poor fuel.
But since you mentioned the fumes, does it produce more than ordinary fumes, or does it have not much fumes but an oily exhaust port. The latter is a sign of poor combustion.

The absence of the grease when you replace the ignition lead should not cause any problem in current circumstances.

Does the carb have limiters on the H and L? 

joe_indi

I missed mentioning one more possibility. Partially faulty oilseals.
Such seals will hold pressure at idle but would allow a bit of air at any other throttle setting. You set H screw for such a saw at WOT and the leaning out due to air intrusion is compensated by opening H a bit more.
When you release the throttle the seal is still leaking and you compensate the higher idle by reducing idle or turning out L a bit more.
But gradually the seals close and the extra air is cutoff, resulting in the saw dying .
Briefly: at WOT the saw is fine if you have moved H out the extra bit. Release throttle it idles normally but rpm drops and engine stalls. If the seals close fast enough the stall will happen as soon as you release the throttle.
I thought I should add this 

Bradford8385

Thanks for posting more. I've been busy and just now getting around to working on the saw again. Exhaust doesn't look oily and choke is opening all the way.
I will check out the piston and flywheel key tonight. The limiter caps are off it at the moment but I'll put them back on too. I always set everything how the repair manual says to. I'll see what I can find

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