MS361 Would not start hot

[jotul8e2]

I started on rather a long day with the chainsaw yesterday about 9:30 am. Ran two tanks of gas through my Stihl MS361 - at which point it would not start again. I had another saw so the day was not lost.

I tried it again about 1:00 pm, 4:00 pm, and about 6:00 pm. A couple of times I think I was able to get a feeble "pop", but it never really fired.

This morning it started on the second pull. I ran about a tank and a half through it with no problems, starting on the first or second pull every time.

Yes, of course it was flooded at various points - you can't pull the started time and again without it flooding eventually. I pulled the plug and cleaned it. No joy.

Any suggestions would be welcome.

 

[Montanalocal]

I have a 361, and had a similar problem. Somewhere I read that once it is hot, to not use the compression release when restarting. That seemed to help with mine.

 

[jotul8e2]

Possibly. But I never use the compression release anyway.

 

[greg13]

Intermittent problems can be like chasing ghosts. You will need to get it to act up again and check for spark, that will tell you what direction to go in. If you have spark look towards a fuel issue, if not something in the ignition is breaking down.

 

[TreePointer]

This issue has been reported with multiple 361's, including mine. The fuel tank breather valve should be letting air into the tank to prevent a low pressure condition, which in turn prevents fuel from being pulled into the carburetor. Unfortunately the valve and its implementation is quirky. I actually replaced mine, but I still got the fuel starvation problem.

SOLUTION: After running the saw for a moderate/long session, turn off the saw and immediately crack open the fuel cap. This lets air into the tank to relieve the low pressure condition in the fuel tank.

 

[dougand3]

Unfortunately the valve and its implementation is quirky

Did Stihl over-engineer the valve? A straw with a duckbill valve has worked for half a century.

 

[TreePointer]

Did Stihl over-engineer the valve? A straw with a duckbill valve has worked for half a century.

I never spent the time to determine what about the valve is different or how it's implementation in the saw is different (wrong stiffness/spring, more prone to clogging in its position, exposed to more heat that changes its properties, wrong filter, et al). Since it was under warranty at the time, I let my local Stihl shop replace it; however, the problem recurred. Maybe after seven years, I should vac test it myself lol!

What I do know is that this has been reported on the 361 in many chainsaw/OPE forums and with my local Stihl shop. Sometimes symptoms clearly presented as vapor lock. I could feel the fuel cap being more difficult to turn, and when it finally opens, you can hear a sucking "smooch" when the cap seal is finally broken (low pressure or "vacuum" condition in the tank) to permit air into the tank. This sometimes was accompanied by observing fuel instantly bubbling out of the tank (lower pressure in tank = lower boiling point).

 

[jotul8e2]

The vapor lock issue does not seem to be my problem. It was after refilling the gas tank that it failed to start., so any back pressure was relieved then. And of course I pulled the spark plug and cranked it a few times to clear any flooding.

The thing that gets me is that the problem persisted for at least seven hours. Then the next morning it fired up immediately. The fact that the few times it even tried to fire were very weak makes me think that something in the ignition - coil maybe - gets hot and shuts down. But if a cool down period is the answer I would have thought seven hours would have done it.

 

[CTYank]

Sounds like classic "plug-whiskering". Chamber deposits flake off randomly and some end up bridging the plug gap. They can be very fine, impossible to see, and solidly ground the plug electrode. I've seen this twice. That can take some magnification, but a credit card or a business card can verify that the plug gap is open. I've also encountered hot-restart problems with "torch" plugs. Now I toss them ASAP and replace with NGK. Problem gone.

 

[jotul8e2]

I cleaned the plug when I had it out, although it did not appear fouled- made no difference. I have a Bosch plug in it now with about 15 hours on it, but now that I think of it I did not remember to gap it. I'll take care of that.

 

[Jags]

Once flooded, Stihl saws are still a bugger to get cleared out. Don't really know why, but even pulling the plug and spinning the engine over doesn' seem to do it for me. I am kinda betting that it started as an unknown flooding that just needed some time to sober up. Just my guess at this point.

 

[jotul8e2]

Problem resolved: final report

Before taking the saw to the shop, I decided to try a new spark plug - even though I knew it could not cause an intermittent problem.

IT WORKED!

I waited this long to report back because I wanted to run it a few times to be sure. I just ran three tanks of fuel through it today with no issues. I have never had a spark plug fail in that manner before in any machine at any time these last 45 years.

The old plug was a Bosch, probably not more than 15 hours on it (10 is more likely). The new plug is a NGK.

 

[Tar12]

I run NGK plugs in everything...quality.

 

[woodhog73]

Did Stihl over-engineer the valve? A straw with a duckbill valve has worked for half a century.

Don't know I've not looked at this but I wouldn't be surprised if they did. They felt the need to make flippy caps for no reason I can think of.

 

[jotul8e2]

Don't know I've not looked at this but I wouldn't be surprised if they did. They felt the need to make flippy caps for no reason I can think of.

The most frightening words from an engineer are, "That works pretty good, but we can make it better."