RPM vs. oil ratio

toyotaracer9 · Sep 23, 2006

ok I have been thinking about this for some time and cant seem to come up with an answer on my own . I am running my saw about 38-40:1 ratio and my rpm around 13300-13400 , the thing I cant seem to figure out is ...... since I am running more oil my saw is gonna run less rpm with the same amount of premix then a 50:1 would run , so would I need to run my rpm even lower since my saw is actually prolly running 13800 if I were to run 50:1 . and no I do not plan on running 50:1 . I hope this makes since to u guys/gals . PS I have the muffler modded .

NWCS · Sep 23, 2006

i run 40:1 and do not get any RPM drops, just keep in mind you do have to re-adjust the carb when changing ratios for peak performance. even the piped 026 i built runs 40:1 and turns 18,000 RPM with ease. on that same 40:1, a woods port 044 runs about 14-15K.

i tune my modified saws in 4 stages
initial tune by ear
check with tach, tune again if needed
check in test log, tune again for peak power in the wood.
check with tach again, make sure peak RPM is safe.

bwalker · Sep 24, 2006

Your saw will not lose rpm with more oil int he mix. Since the fuel air rstio is leane dout it may actually run faster.
If your loosing power with more oil you have other issues, such as overly rich carb settings.

toyotaracer9 · Sep 24, 2006

bwalker said:
Your saw will not lose rpm with more oil int he mix. Since the fuel air rstio is leane dout it may actually run faster.
If your loosing power with more oil you have other issues, such as overly rich carb settings.

I will have to disagree with this , even though there is less gasoline the volume is taken up by oil so there wont be a lean condition . and I understand that there wouldnt be a great difference between 40:1 and 50:1 on rpm but the 50:1 should run faster , for example if u run a saw at 50:1 then at 16:1 with the same carb setting the saw isnt gonna run nearly as fast on 16:1

I guess all I really need to know is , can I run my saw at 40:1 at 13500 and be as safe as 13500 @ 50:1 ?

bwalker · Sep 24, 2006

I dont know what to say other than that you are misinformed.
Barring a mechanical problem your saw will run great at 32:1, 40:1, or 50:1 if the carb is set properly.

toyotaracer9 · Sep 24, 2006

bwalker said:
I dont know what to say other than that you are misinformed.
Barring a mechanical problem your saw will run great at 32:1, 40:1, or 50:1 if the carb is set properly.

you mean set properly for each mix ? or set the same for all mixes ?

I never said the saw wouldnt run great on any specific mix , I am just saying that adding oil to gasoline makes the gas less volitile , from 40:1 to 50:1 isnt much but to 16:1 there has to be a difference in rpm if u leave the needles set at one spot . and there is no problems with my saw I am just trying to be sure I dont need to run the saw at a diff rpm due to running a lil more oil .

bwalker · Sep 24, 2006

Tach the saw to its normal setting each time you change mix ratios. keep in mind the differance is miniscule, but you will need to richen the saw ever so slightly if you are going from say 50:1 to 32:1. A 15 degree change in ambieant air temp will have a much larger effect than a 1% change in oil content.