Interesting find troubleshooting MS261 C-M hard start issue

[huskihl]

I haven't yet. Is it safe to pressure and vacuum test without detaching the carb? My only concern about removing the carb is that I presume there'd be at least one gasket involved and I don't have any spare gaskets at this moment.

The carb is outside of the vacuum test area. Nearly impossible to seal off where the shafts go through the carb body, as well as the other orifices inside. I use a piece of rubber or duct tape between the carb and boot and tighten the carb down to seal it

 

[MustangMike]

I made a metal plate to go over a piece of bike tube rubber, then drilled holes through small pieces of Oak to replace the carb.

Makes it easier to put the pump fitting on the impulse line.

The Exhaust is just the metal plate and bike tube.

 

[huskihl]

I made a metal plate to go over a piece of bike tube rubber, then drilled holes through small pieces of Oak to replace the carb.

Makes it easier to put the pump fitting on the impulse line.

The Exhaust is just the metal plate and bike tube.

Ahh. I just test through the plug hole and always block off with the carb and muffler

 

[Ketchup]

@vdavidoff, at this point I wouldn’t pressure test the saw unless you have the tools and know-how. It’s very likely the new solenoid will fix your problem. Try that first since you already paid for it.

If that doesn’t work, pressure test the saw before throwing more parts at it. If you have never pressure tested a saw, there are excellent YouTube videos that will explain it.

Based upon what you have written here’s what I think happened:

You ran your saw on pump gas (presumably with ethanol in it) that was probably winterized. Winterized gas vaporizes at a lower temperature so in hot conditions it vapor locked the solenoid (it’s possible that alone damaged the solenoid). You then super cooled the solenoid (that may also have damaged it).

You shelled out $20 for some quality gas and that helped, but the saw is still finnicky. In six tanks, it should have re-tuned itself. If it’s still boggy and annoying in hot conditions, I would say your Solenoid IS damaged now and the saw is running too rich in all conditions.

So change the Solenoid and stop running ethanol pump gas. If you can get non-ethanol at the pump, great! Just make sure it’s not winterized. I don’t run canned gas because it’s a racket, but if you don’t have quality gas available and you don’t want to have trouble with your saw, $100 a year isn’t really that much to pay.

 

[DND 9000]

I also recommend canned gas, because it has much less toxic incredients as pump fuel. That means you breathe a lot less toxic things like benzene, aromats, toloul and so on. Years ago I also used pump fuel and had always a terrible headache after cutting with the saw, brushcutter or working with other machines. Now I only use (what you call canned gas) alcylate fuel like Aspen, Stihl Motomix or other brands. I feel a difference with the headache for me, it`s much better. If I work long enough I still can get a headache, but other factors like drinking enough water during the work is also importand. Professional landscapers, loggers and also private firewood cutters which cut in the woods have to use this and also biodegradeable chain oil by the law here. This canned fuel is also better for the fuel components of the machine you use, they last much longer and there is no need to run the fuel system dry if the machine is stored for a longer period.

 

[Lightning Performance]

I'd like to chime in with a few quirks my rock stock 362 has come up with on it's own but the fuel or water was always the problem, so far.

Should have never opened this thread today.

Anyway...
362 first or second year saw with Mton I V1 type.
The winter pump gas is fine till you get into summer months with chainsaws on winter mixed pump gas. Mine will surge just of idol. It sounds like a blown pro mod or top fuel ride. I kid you not. Change the fuel to from 89 winter to summer 92+ or boat gas and it's gone. Siphoning out the water or letting your tanks dry out for an hour or three in the sun really does help keep the water buildup out of your fuel tank. Mine get drained often by siphon when running pump gas. I collect it in a clean glass jar. Water collects at the bottom. Saws that sit are the worst on E10 fuel. Won't even consider E20. Getting a batch of already "wet" fuel could be a nightmare. Read on and understand why I believe this to be so.

The boat gas has nothing in it but gas and no lead. The saw, my saws in all forms, overall run better in 90-100 heat on pump boat gas 95 octane. That is not always an option here so the next few trips I'm taking 18 gallon barrels to fix that problem each trip.

These fuel boiling issues are very apparent in my 6401, 034 and any of my 362's Mtron or not. Seen it with my own eyes, again, last week. Bubble bubble wtf... winter gas is all gone now and testing is over with it.

My fuel cans stay sealed now days. No sun, no moisture and no rain on them ever like always. The water can developed from vented cans and then collects in the bottom of your tank after you mix it. I'm betting the mix oil displaced the absorbed water as the fuel mix heats up in your tank. Separating fuel, oil and water in the carb is more than likely the start and root cause of many of these problems. No Mtron, no problem cause it will clear on it's own or smoke the motor. Think about what I'm saying here.

The 362 mtron saws starts to stutter like any other when running out of fuel and has been run bone dry many many times up a tree. Fuel it and let it idol for one minute or it does nothing but hesitate and quit. After that let it warm up a few minutes at idol, I do. Then hold it wfo for thirty seconds and lay it in some wood for at least fifteen seconds cutting. Done zero issues. Starts all day on one pull. Cold starts on one or two in the morning or first use. Sits with pump gas in it or boat gas. It has never been in long germ storage here to need aviation fuel and stabilized oil also. Never been reset.

It has been run over before. Busted off cylinder fins.
Bought it from DJ right here on ope.
Nothing else to tell.

GL

At 9500' I'd imagine the M-Tronic system have a devil of a time running lean enough.

And, opening the muffler may make it worse.

Ahh. I just test through the plug hole and always block off with the carb and muffler

I recommend using the decomp hole first if it has one. Avoids newbie mistakes or poor readings if your running a leak down tester type tool. My 2ct for the fourth

Saw On

 

[Hobbylogger]

I was looking for a place in my area that sells off road diesel, when I found I they also sold ethanol free 92 or 93 octane gas. This place also delivers fuel to farmers, trucking companies…. In bulk. Although it’s an extra $1 gallon I’ll pay it as long as he sells it.


Sent from my iPhone using Tapatalk

 

[huskihl]

I'd like to chime in with a few quirks my rock stock 362 has come up with on it's own but the fuel or water was always the problem, so far.

Should have never opened this thread today.

Anyway...
362 first or second year saw with Mton I V1 type.
The winter pump gas is fine till you get into summer months with chainsaws on winter mixed pump gas. Mine will surge just of idol. It sounds like a blown pro mod or top fuel ride. I kid you not. Change the fuel to from 89 winter to summer 92+ or boat gas and it's gone. Siphoning out the water or letting your tanks dry out for an hour or three in the sun really does help keep the water buildup out of your fuel tank. Mine get drained often by siphon when running pump gas. I collect it in a clean glass jar. Water collects at the bottom. Saws that sit are the worst on E10 fuel. Won't even consider E20. Getting a batch of already "wet" fuel could be a nightmare. Read on and understand why I believe this to be so.

The boat gas has nothing in it but gas and no lead. The saw, my saws in all forms, overall run better in 90-100 heat on pump boat gas 95 octane. That is not always an option here so the next few trips I'm taking 18 gallon barrels to fix that problem each trip.

These fuel boiling issues are very apparent in my 6401, 034 and any of my 362's Mtron or not. Seen it with my own eyes, again, last week. Bubble bubble wtf... winter gas is all gone now and testing is over with it.

My fuel cans stay sealed now days. No sun, no moisture and no rain on them ever like always. The water can developed from vented cans and then collects in the bottom of your tank after you mix it. I'm betting the mix oil displaced the absorbed water as the fuel mix heats up in your tank. Separating fuel, oil and water in the carb is more than likely the start and root cause of many of these problems. No Mtron, no problem cause it will clear on it's own or smoke the motor. Think about what I'm saying here.

The 362 mtron saws starts to stutter like any other when running out of fuel and has been run bone dry many many times up a tree. Fuel it and let it idol for one minute or it does nothing but hesitate and quit. After that let it warm up a few minutes at idol, I do. Then hold it wfo for thirty seconds and lay it in some wood for at least fifteen seconds cutting. Done zero issues. Starts all day on one pull. Cold starts on one or two in the morning or first use. Sits with pump gas in it or boat gas. It has never been in long germ storage here to need aviation fuel and stabilized oil also. Never been reset.

It has been run over before. Busted off cylinder fins.
Bought it from DJ right here on ope.
Nothing else to tell.

GL


And, opening the muffler may make it worse.

I recommend using the decomp hole first if it has one. Avoids newbie mistakes or poor readings if your running a leak down tester type tool. My 2ct for the fourth

Saw On

If it doesn’t pass, the decomp is the easiest place to check, right next to where my tester is plugged in. Most decomps don’t leak on pressure, so it’s a dead giveaway if they hold pressure and not vacuum. 9 times out of 10 all I have to do is twist it to seal it and hold it in place if that’s the case

 

[MustangMike]

Well, when I plug into the impulse line, them I'm also testing the plug and decomp.

 

[huskihl]

Well, when I plug into the impulse line, them I'm also testing the plug and decomp.

Difficult on a 261…

 

[MustangMike]

Wow, yea! I guess I'm just fortunate that I only work on 440/460/461/660 saws!

Makes it easier, I only need two "banks", one for the intake, one for the exhaust. The bolt spacing on all of them is the same.

 

[vdavidoff]

I appreciate all the thoughtful replies. I don't know if I'm bad at searching, or just gave up too quickly, but this is one of the most useful threads on this issue I have run across.

Regarding canned fuel, yeah, if ultimately it seems like I need to do that, I will, it'll just be a lot more than $100/yr. I am not sure how many gallons I run through my saw in the warmer months but it's a lot. I essentially live in the forest so there is no shortage of stuff at which to point a chainsaw, though at the moment I focus almost exclusively on deadfall.

Also I don't think it was mentioned until a few comments ago but I have had fuel boiling since I first got the saw. The first summer I had it when it started acting up this was the first thing I noticed that seemed obviously weird (to someone who hadn't spent much quality time with a chainsaw at that point, at least). The dealer I bought it from said another customer had the same issue (including hard/nearly impossible starts) and that they had sent the saw off twice for some mothership to look it over, and both times it was reported that there were no issues with the saw (i.e. it never got fixed). Right or wrong I allowed that to set expectations regarding getting work done on my saw for similar issues, so I've tried to just tackle it myself. My saw has always boiled fuel far as I know, though I rarely have reason to open the tank with enough gas in it to notice. When I originally researched this I came to the conclusion it was considered normal, but maybe it has been a sign of winterized and/or crappy gas all along, or otherwise, not OK.

I suspect my solenoid will arrive this week if I'm lucky...

 

[drf256]

The low atmospheric pressure at 9500’ combined with heat will make fuel boil faster than for others.

Hoping the solenoid fixes things for ya. It’s conceivable that it’s malfunction isn’t complete, it just can’t compensate for your situation.

My point all along is that usually one has to check everything else before blaming the MT. The only reason I’ve even suggested it is because I’ve been in your shoes many times.

Replacing the solenoid seems easy and cheap enough. If it’s not that, you’ll have a backup. I’ve had the same issue as you do with manual tune saws in the summer heat and I am at 230psi ASL.

 

[67L36Driver]

Difficult on a 261…

View attachment 300630

Plug those with a 1/2” drive socket. Square hole taped over and a golf ‘T’. [emoji106]

 

[Ketchup]

If you’re burning more than a few gallons per year I can see why you wouldn’t want to buy canned gas. Like I said, I don’t. I run 87 e-free from Murphy Express (yes, off the pump.). There is a period every spring where hot starts are more prevalent, but we’re running 25+ saws off the stuff year round 4 days per week and haven’t had a recurring hot start problem in years. I live at 9,400’ and run the same 87 e-free without issue. My 261 is a standard carb but my 201tc-m runs just fine.

I used to run 91 AV-Gas low lead, but it turns out “low lead” is still quite a lot. I also think a lower octane fuel burns better at elevation. If you do go with canned gas I would try to get a lower octane variety. 91 or ideally 87.

 

[vdavidoff]

Chainsaw is 100% again.

I ran a tank of the not-crap pump gas through it and it ran about the same as I described with the canned gas, but seemed a bit more powerful and consistent. Still off a bit though. I then replaced the solenoid, reset m-tronic, and it sounded better immediately, as in when I was doing the m-tronic reset even. I ran two tanks of not-crap pump fuel through it and it was great on the first tank, and seems to have gotten a bit better on the second. At this point it works the way I'd expect it to. No funny business getting it started at any point (if it has sat a while it takes a few pulls but it seems totally reasonable), no bogging or power issues, no dying. I can even shut it off whenever I want without fear that it won't start again.

I'd say my problem was 80% crappy fuel and 20% the old style solenoid.

Thanks again for all your help. I really appreciate it. And thanks for humoring me while I tried to figure this out. This has been a great learning experience.

 

[RI Chevy]

Good deal. Glad you got it fixed.

 

[MustangMike]

What he said!

 

[Brewz]

Once they go rich Tony, they can take a LONG TIME to correct themselves. I had a 362 that took about 10 tanks and a 261 that took about 6 tanks (the 261 happened after I let someone else run the saw).

They both ran fine after they corrected, but it took a long time. Had to start them in the run position with the trigger pulled (easier with two people).

This saw would start out running fine and then just go super rich all of a sudden at random times.
Problem moved to my saw when solenoid was swapped.

 

[vdavidoff]

Just a bit of a follow up here. The saw started acting up again this season. I went and spoke with the powertools/chainsaw guy at the Ace in Colorado City (I think his name is Bill) and he knew what I was going to ask before I even opened my mouth. He confirmed everything we've discussed in this thread/I have learned to mitigate the issue, and said aside from replacing the solenoid, the ethanol is the biggest pain point, combined with heat and altitude. He said a non-M-Tronic saw would still be problematic, as would another brand (I had originally gone up there because they see Husqvarna and I wanted to find out if one of those might do better for me).

So the short version of how to mitigate this issue - that being hard or no start after the saw has been run an hour or two:
* If you have the old style white MTronic solenoid, replace it with the newer black one
* Use ethanol free gas - I'm currently using Trufuel from Home Depot because I don't think I can find a station with ethanol free gas near me to mix my own, but I'm still looking
* When you're experiencing a hard start, restart the saw with the trigger pulled full throttle. It'll still be a little finicky but that seems to be the best way to get it running relatively quickly. It may still want to bog or cycle weird for the first bit after start up, but if you keep giving it gas and playing with the throttle when it sounds like it wants to die, it'll get running again.

Andy