Stihl ms391 woes

[LAWN BOY]

Here are some piston pics. I pulled the plug which looks new and pulled the saw over a lot. Seemed flooded. Reinstalled plug and gave it a thimble of mix down the carb and problem still remains. Any chance the carburetor is just dumping that much gas into the engine causing it to do this, is that possible?

 

[hacskaroly]

Seemed flooded

If the saw seems flooded, put the lever on run (not choke or fast run) and just pull upwards of 20 times, at some point it will start popping and even run. I had many customers that brought in saws in this condition and it just took pulling it until it fires. I was just working on an 034 and after replacing the piston could not get it to fire. It popped once and I just put it down to come back to it. A couple weeks later went to start it and it fired right up - it shut down a couple of times while adjusting the carb and somehow ended up flooding it. Realizing what I did, gave it about 20 pulls and it fired up.

 

[Wood Doctor]

However, some saw engines will not start after being flooded, regardless of how many non-choked pulls. I usually just let them sit for half an hour and use another back-up saw that runs. They almost start right up after watching another saw take their place. Sometimes chainsaws are half human.

 

[Woodwackr]

I have pulled the plug and flipped the saw upside down and pulled the cord a few time to clear a very flooded saw.

Have you pulled the carb and checked the diaphragm and pump flaps?

 

[LAWN BOY]

I have pulled the plug and flipped the saw upside down and pulled the cord a few time to clear a very flooded saw.

Have you pulled the carb and checked the diaphragm and pump flaps?

I did have it upside down but didn’t pull upside down. Thanks for letting me know.
I haven’t pulled the carb yet. I can do that next I suppose.

 

[Woodwackr]

I did have it upside down but didn’t pull upside down. Thanks for letting me know.
I haven’t pulled the carb yet. I can do that next I suppose.

Carb is the most likely cause.

 

[LAWN BOY]

Carb is the most likely cause.

I hope that’s all it is. I’ll probably work on it this weekend.