MS400C Won't Start

[benmyers]

I rebuilt an MS400C recently. It had a chunk broke off the top of the piston, I believe was straight gassed. It got a new OEM piston and cylinder.

Saw went together fine and has a ton of compression. The saw will fire but will not stay running. I have tried about everything, including cleaning the carb. I am not sure what else to do. I have rebuilt countless saws, but I have not worked on any of these saws and have minimal experience with the M-tronic system.

Any ideas what the issue could be?

 

[jacob j.]

This would probably be best in the Chainsaws section @Mastermind @Woodpecker

 

[Woodpecker]

This would probably be best in the Chainsaws section @Mastermind @Woodpecker

Dund

 

[Mastermind]

I rebuilt an MS400C recently. It had a chunk broke off the top of the piston, I believe was straight gassed. It got a new OEM piston and cylinder.

Saw went together fine and has a ton of compression. The saw will fire but will not stay running. I have tried about everything, including cleaning the carb. I am not sure what else to do. I have rebuilt countless saws, but I have not worked on any of these saws and have minimal experience with the M-tronic system.

Any ideas what the issue could be?

Does it seem overly rich, or too lean?

 

[066 redeye]

If mtonic bad wiring to the solenoid will kill spark if the solenoid is not "seen"

 

[farminkarman]

As @Mastermind mentioned, does the plug look wet or is it bone dry?

 

[bogieboy]

When i rebuilt my ms661 mtronic i had to "help" it to get going by giving a squirt of mix down the throat for the first run, and then go imediately into a reset to get it to learn the new happy mix with an intact piston vs the one that spit a circlip and hung the wristpin in a port... if your saw is an mtronic 3.0, its stupid simple... start run stop lever in start, start saw, let idle 30 sec, then pin the throttle, the mtronic will hold it on a limiter for the next 30 sec at about 3/4 speed, then once the saw revs full throttle, go ahead and shut down, then restart saw... should idle after that.

If its mtronic 2.0, set to start, get running, leave in start for 90 sec. Shut down, restart and go cut a nice easy cut or 3

Saw will say on the sticker by the handle in one of the corners, m2.0 or m3.0

 

[drf256]

The default on a bad solenoid, or improper wire connections, is pig rich. Does the saw stink like gas when it stops running, or does everything seem dry? Had a guy bend the pins on the wiring harness once on a 261. Saw would just flood itself.

Are you certain what ruined it the first time? Even though it’s MT, the normal problem solving is needed. It’s actually rarely the MT itself. Have to check the filter, impulse, fuel line, etc…

I had a saw last year that had intermittent problems. I got so frustrated with it that I split the case and did a ground up rebuild on it. In the end, I found a tiny crack in only the neck of the oem fuel filter had I not disassembled and gone through each individual part, I never would have found it.

Unfortunately, youll need to go through every part of the fuel system as well as vacuum test the saw until u find the issue.

 

[Oldbuzzard]

I rebuilt an MS400C recently. It had a chunk broke off the top of the piston, I believe was straight gassed. It got a new OEM piston and cylinder.

Saw went together fine and has a ton of compression. The saw will fire but will not stay running. I have tried about everything, including cleaning the carb. I am not sure what else to do. I have rebuilt countless saws, but I have not worked on any of these saws and have minimal experience with the M-tronic system.

Any ideas what the issue could be?

I work on a lot of Mtronics, as well as sawing myself. I would replace the solenoid first thing without hesitation. Cost about $50. When I bought my own, new 400C a couple of years ago the solenoid crapped the second or third day I used it.

 

[benmyers]

Sorry for the delay guys. I do not know for sure what killed it the first time. I have a customer/friend who burnt 3 pro saws up all together. a 461, Husky 575, and this MS400C. I believe they didn't mix a can of gas, but wasn't able to prove it. The 575 had no oil. The 461 was mixed but I think they mixed and refilled. The 400C I couldn't get to in time so it was taken to a dealer. I got the box of parts after they quoted $900+ to rebuild it.

I have since noted that the coil does not spark unless I yank it HARD. This seems abnormal to me. Saw definitely seems rich but I am not sure why.

I have a coil and a solenoid coming. I will find out which it is and report back.

I appreciate the help

Ben

 

[066 redeye]

think mtronics take a fair speed to spark.

 

[benmyers]

Hey guys. I replaced the coil and it makes no difference. Replaced the carb and it still won't start or run. I pulled the saw back apart to inspect everything as I go back together. So far I don't see anything obvious. Almost acted like it wasn't getting gas. impulse line/path looks good, sealed good. Fuel line has no cracks. Filter is not plugged.

I will continue and report back. I will be about out of ideas after that.

 

[066 redeye]

So it has spark?
What happens if you give it a squirt of fuel in the carb?

 

[lehman live edge slab]

Did you just change the solenoid in the carb or put new carb on? When you cleaned the carb at first did you check the metering lever hight?

 

[benmyers]

It does have spark when yanked hard. Nice blue spark. I will get it the rest of the way back together and try it again this evening.

 

[benmyers]

Did you just change the solenoid in the carb or put new carb on? When you cleaned the carb at first did you check the metering lever hight?

I swapped an entire new carburetor. I visually checked the metering height but did not check popoff or anything. I considered the metering lever since it doesn't seem to be getting fuel, but it is odd that both carbs may be doing this.

 

[lehman live edge slab]

I swapped an entire new carburetor. I visually checked the metering height but did not check popoff or anything. I considered the metering lever since it doesn't seem to be getting fuel, but it is odd that both carbs may be doing this.

Carb was new? With new solenoid?

 

[lehman live edge slab]

Carb was new? With new solenoid?

If it was I’d start looking at the harness for bent or dirty connections

 

[benmyers]

I got this put back together and it still will not run. It does pop off but doesn't fire up and run. It seems like it isn't getting adequate fuel. I checked the impulse passage, fuel line, etc. again when I had it apart and didn't see any issues.

I am running out of ideas. Both carbs and both coils do the same thing basically, so it doesn't seem to be either of those.

 

[benmyers]

Carb was new? With new solenoid?

Yes, brand new carb with new solenoid.