Run away Mac

[flipjack]

I got an old Mac 797 that revs up on its own without me giving it gas! It starts o.k & idles. After giving it full throttle, it will rev down a bit, then rev up again on its own. The throttle doesn't seem to be stuck, and I'm at a bit of a loss as to why it is doing this? The only thing I have done to the saw since I bought it was fix the gas tank leak. Any ideas?

 

[Crofter]

Check the throttle closing spring.

 

[heviarti]

It's sucking air through the crank seals. If you don't want to rebuild it, run a heavier mix, because the air from the seal side leans your fuel AND your lube. more oil == your saw won't die a screaming death.

Also, possibly look at the governor.

 

[flipjack]

Thanks for the input

 

[Mange]

Is problem fixed?

Mange

 

[flipjack]

Nope. Haven't had time to look into it. I may just get rid of it.

 

[heviarti]

ok.. is she a 797 or a super 797? i work my big macs.. would be willing to rebuild another to run.

 

[Mange]

Try this

I have been experementing a little.
Myby the carb is set a little too lean.

Mange

 

[flipjack]

I'm not sure if it's a super 797 or not. Any way of telling? I'll try adjusting the carb and see what happens.

 

[Mange]

Tell how it worked out.

Mange

 

[Greg Carberry]

One thing I always do before I tune an old saw is replace the crank seals and check the gaskets. Its easy to do and cheap saves alot of time and frustration instead of chasing air leaks.

 

[weimedog]

If your going to sell it...drop an email. Might be interested.

 

[heviarti]

Originally posted by flipjack
I'm not sure if it's a super 797 or not. Any way of telling? I'll try adjusting the carb and see what happens.

real easy to tell.. big honkin carb or cube? cube == super