how to vacuum/pressure test ms391

[smithfix]

I'm working on a ms391 and it starts but wont power up past a little over idle and struggels to do that, taken carb off and apart 5 times no change . p/c is brand new and carb looks great, Can it be lack of pull from impulse from case ? theres no line so how do I test this modal or any other thoughts ?

 

[Westboastfaller]

A coil going out of time will do just that. Usually will see gas leaking out of the muffler.
Mostly common with 365/372 Limiter coils but have seen it with Stihl 361.

preasure testing? make it happen man. Pull the mufler and make a block plate and drill it, use the gasket or piece of rubber and screw it back on. pull fillter and make a block with a tire stem and sink and pump with hand pump or foot pump or hook into the impulse line. Now see what you can come up with and show us.
Deal?

 

[smithfix]

A coil going out of time will do just that. Usually will see gas leaking out of the muffler.
Mostly common with 365/372 Limiter coils but have seen it with Stihl 361.

preasure testing? make it happen man. Pull the mufler and make a block plate and drill it, use the gasket or piece of rubber and screw it back on. pull fillter and make a block with a tire stem and sink and pump with hand pump or foot pump or hook into the impulse line. Now see what you can come up with and show us.
Deal?

Ive vacuum tested saws with impulse lines before but this modal has a rubber/plastic intake with a small hole in it for carb. Do I plug it and adapt a piece for the main carb opening outa rubber or plastic and the upper opening with the vacuum tube in one ? having problems loading pic

 

[smithfix]

 

[Westboastfaller]

Yeah like a 1/4 " rigid rubber for exhaust and intake. So it looks like it has an internal impusle like a 357.
One of the intakes have to have a line and spure or stem/fiting right?
If that is an lineless impulse.

Keep your blocks small especially on exhaust side so they don't impede your vision on pinpointing a leak.

I have a 2 oz syringe I use to test carbs..works good

 

[Chainsaw Jim]

Rebuild the carb if it has not been rebuilt. Diaphragms will look ok when they're not and fool you into tearing your saw down for nothing.