Too big for a 660?

[Charlie Coyote]

A lot of saws are tuned extremely lean from new (when they should be run a bit rich). Adding more oil may only change it a fraction, but that fraction may be what raises the temp 1° over critical.
Even changing oils can make a difference... moral of the story is to tune for what your mix is

I found this YouTube video on the very subject very informative by Dave's Small Engines. It compares effects of different ratios of mix. Sounds like you might use the input, too.

 

[sean donato]

Do you really believe that the difference between 50:1 and 40:1, which is .6 oz. makes a saw so much leaner that it somehow jeopardizes

It's already been more then proven that oil displaces fuel in the mix. It may not get you today or tomorrow but yes it will eventually bite you. Your video only proves you need to re-tune for different mix ratios. Truthfully I don't care what you do with your saws or two strokes engines, tune them, don't tune them doesn't make a difference to me.

 

[J D]

That video just reinforces what we were saying... He added more oil & the saw ran hotter. More oil isn't going to cause more friction so that isn't the cause of the heat, & oil doesn't burn hotter than fuel so that can't be it either... The increase in temp is due to the leaner running condition caused by adding more oil & not re-tuning accordingly. It is also clear his saw was running rich from the start, had it been tuned on the lean side to start with I'd wager the results would have shown higher temps & a greater variation

 

[Charlie Coyote]

25:1 is double 50:1. There are a lot of saws fried at 50:1 and more running in excess of two decades at 32:1 and 40:1. Amsoil Saber synthetic 2 cycle is the only 100:1 that I know of. Numerous other YouTube video is up on it with the producers' testimonies of decades of use at 80:1. Not to mention a lot of loggers and woodies that swear by 32:1 and 40:1 never cooking the engine. After frying my Husqvarna 359 at 50:1 and buying two new saws I decided to run at least their set in at 40:1. I'm liking everything I see and saw so far. My beans.

 

[sean donato]

25:1 is double 50:1. There are a lot of saws fried at 50:1 and more running in excess of two decades at 32:1 and 40:1. Amsoil Saber synthetic 2 cycle is the only 100:1 that I know of. Numerous other YouTube video is up on it with the producers' testimonies of decades of use at 80:1. Not to mention a lot of loggers and woodies that swear by 32:1 and 40:1 never cooking the engine. After frying my Husqvarna 359 at 50:1 and buying two new saws I decided to run at least their set in at 40:1. I'm liking everything I see and saw so far. My beans.

I really need to find the article again, but husqvarna reccomends anything over 60cc to be ran on 30 or 33 to 1. Really here in the states the epa has driven the lean mix ratios and lean fuel settings. Its a shame really as it doesn't really do the equipment any favors. Now saying that most modern 2 stroke oils do their job very well. That still doesn't negate the need to tune for the mix ratio your running.

 

[Charlie Coyote]

Yes, by all means, tuning the carb for conditions is a must. I do by erring to a rich mix at idle and under full load, so that I hear the saw four stroke when letting up in the cut with an instant response from idle to full throttle. I'm running 40:1 VP Racing 2 cycle and 91 octane straight (non-ethanol) gas. The Echo CS620PW and the Holzfforma G660 PRO seem to like it. Removing the muffler to inspect the piston it's bathed in mix and looks polished. There's no excess carbon anywhere. Always tune 'em.