SOS. MS440 refuses to do anything.

[Alphadelta]

This saw. Will be the death of me.

I want to preface that prior to this the saw was running fine.

Took it up to help a friend buck up some wood. Got my 440 running but it was very sluggish, gave it a second and it just slowly dropped the rpm and died. Check my carb settings. They were fine. Restarted. Ran worse. Died quicker.

From here out the saw never starts. I’ve checked the following.

1. Spark plug
2. Fuel
3. Compression
4. Impulse line
5. Exhaust is clear
6. Fuel tank breather
7. Switch

Basically I’ve done everything I can think of. It’s got gas, spark, and compression. Everything should be fine. I know it’s not the gas because I brought a Husq saw using the same fuel and it never gave me any issues.

Does anyone have ideas? I got it home. Aired it out. Tried a new spark plug. Triple checked everything and I get fuel but it doesn’t even try and start now.

Before I go tearing into anything does this sound characteristic of anything I’m missing.

Thanks in advance for any advice.

 

[Maintenance supervisor]

If the spark is weak its not going to ignite fuel, could be the ignition or the flywheel key.

 

[Alphadelta]

So short of just putting a new one on. Is there anyway to check that?

 

[user 122190]

It’s got gas, spark, and compression.

Flooded? I'd blow it out as best you can with compressed air and give it another go. Remove the plug, gas tank empty, air filter off, WOT and blow it clean while slowly pulling the engine over. Do it a lot and really really make sure it is dry. Then before putting gas in, reinstall the plug and see if it will cough or even run a bit.

 

[Welder56]

Bad fuel line maybe? I’m not all that good at this game but possibly it’s not getting fuel. Storing fuel in the tank doesn’t do the lines any good. If it’s real squishy then it could be collapsing.

 

[atpchas]

I assume "Exhaust is clear" means you checked the spark arrestor. If not, ...

 

[rupedoggy]

What is the exact number of the compression?
If you want to check for a good coil, increase the gap to about a quarter of an inch. If it still jumps and sparks, probably OK.

 

[thompsoncustom]

I would check the flywheel key and make sure it's not broke. U can have fuel, spark, and compression but if the timing is far enough off it will never start.

 

[stihltech]

Pulse hose connected below cylinder and not cracked?

 

[heimannm]

I don't see an examination of the fuel filter on your list.

Mark

 

[Bob_w]

I would check the flywheel key and make sure it's not broke. U can have fuel, spark, and compression but if the timing is far enough off it will never start.

Yes, I just got a MS391, the flywheel timing turned out to be the problem. The key must have been sheared by the previous owner. I have another MS391 apart on the bench, so I exchanged the plug, spark module, Re-gapped the module. No results. I pulled the flywheel, it had a messed up key. I had to file away some of the key without messing with the taper to get it to set on right. Line it up, torque it up. The saw ran real fine. Something to look at.