Poulan pro 42cc rpm fluctuating

[Deanpeddle]

Hi folks, I have a poulan pro 42cc. It starts fine but then rpm starts fluctuating (external tach attached). It’ll go from (for example) 2500 up to 2700 drop back again then up to 3800, back to 2700 and so on. (Not touching throttle). If I turn it on it’s side (ie chain running horizontal) it’ll race up to 4500 or so. (Again no throttle). Of course, as rpms increase chain starts turning. Sometimes if I tip it from horizontal back to vertical it will shut off.

What’s the most likely cause of the rpms fluctuating like that?

 

[Deanpeddle]

Hi folks, I have a poulan pro 42cc. It starts fine but then rpm starts fluctuating (external tach attached). It’ll go from (for example) 2500 up to 2700 drop back again then up to 3800, back to 2700 and so on. (Not touching throttle). If I turn it on it’s side (ie chain running horizontal) it’ll race up to 4500 or so. (Again no throttle). Of course, as rpms increase chain starts turning. Sometimes if I tip it from horizontal back to vertical it will shut off.

What’s the most likely cause of the rpms fluctuating like that?

May 20/2019 ... hmmmm still no reply after a week!?!? Is this a tough question or am I doing something improper? Should this question be in another forum?

 

[Bobby Kirbos]

It sounds to me like the crank seals are kaput. It's a 42cc clams hell engine. There should be 4 Torx screw heads accessible from the bottom of the saw. Make sure they are good and tight. If you tighten them and the problem persists, you more than likely need new crank seals.

On these saws (which are made to be 1 shade better than disposable), it's up to you whether or not it's worth your time and the parts cost (or if you should just go buy a new saw).

 

[Kostas]

May 20/2019 ... hmmmm still no reply after a week!?!? Is this a tough question or am I doing something improper? Should this question be in another forum?

You most likely have an air leak somewhere,a pressure/vacuum test is in order.

 

[Deanpeddle]

Thanks ! Appreciate the help

 

[Brent Nowell]

Honestly the metering diaphragm is what controls fuel volume to the engine. Turning the engine upside down and having the rpms change that much indicates a stiff diaphragm.

I would take the carb off and check it. One place of MANY to start with symptoms like this.

 

[Deanpeddle]

Thanks v much! I will def. start there

 

[Gord404]

Maybe check and see if your carb is tight, might get lucky.

 

[Deanpeddle]

Hi folks- it seems an air leak was the problem. I tightened the 4 torque screws underneath the carburetor and the saw is running fine now.
THANKS for your help!

QUESTION: does anyone know the min and max rpm settings for this saw?

 

[Bobby Kirbos]

I've looked for that number as well, with no luck. It appears it's a closely guarded trade secret.

Tune it in the wood.