RPM on 660 BB kit?

[chainsaw1]

Just wondering what to set the RPM 2 on my BB kit fot the high end?

 

[Lakeside53]

There is no magic number. As there's no rev limiter on the coil, It's at the point it naturally "4-strokes".... but less then "too much".

Anything less then about 13,500 wouldn't be unreasonable (but you still need to figure out what the correct rpm is), but it will depend on your muffler and how the ports on the BB were messed with in comparison to the OEM.

 

[ShoerFast]

Sounds like a good place to do a few timed cuts?

In a big log, one the bar just spans, letting the saw do the work.

Starting to rich, stop-watch the time it takes to cut a cookie.

Just for a say, say......

1 1/2 turns out with the 'H' takes 14 seconds...

1 1/4 turns out with the 'H' takes 13 seconds

1 1/8 turns out takes 12 seconds

1 turn out takes 13 seconds,,,,,,

Your AF ratio is somewhere between 1 1/8 and 1 1/4

Every saw/engine or every B/C on every saw will be slightly differant, but the fastest timed cut is your best AF ratio.

When you know your at your best timed cut, take a tach reading of your WOT so you can re-set your 'H' with-out timed cuts.

 

[timberwolf]

Don't expect the RPM from a BB kit to be the same as stock, they often rev a bit lower due to the porting differences. However with porting the BB 066 will turn up in the 14,500 to 15,000 range as a work saw.

 

[Crofter]

SNIP>There is no magic number. , It's at the point it naturally "4-strokes"....
SNIP> but it will depend on your muffler and how the ports on the BB were messed with in comparison to the OEM.

The setting where it clearly 4 strokes with no load at full throttle but goes to two stroking within half a second when it comes into the cut.

Shoer's method will get you there too, though "power tuning" for the shortest cut time might be just a little shy on insurance! To be safe, maybe just a tad richer than fastest cut time. Try both methods and see how close they come to the same needle setting.

I have run some of Timberwolfs Big Bore mods before and after re porting, some with carburetor bore mods etc., and it is true that the factory recommended max no load rpm is meaningless then as a comparison.

 

[Tzed250]

The setting where it clearly 4 strokes with no load at full throttle but goes to two stroking within half a second when it comes into the cut.

Shoer's method will get you there too, though "power tuning" for the shortest cut time might be just a little shy on insurance! To be safe, maybe just a tad richer than fastest cut time. Try both methods and see how close they come to the same needle setting.

I have run some of Timberwolfs Big Bore mods before and after re porting, some with carburetor bore mods etc., and it is true that the factory recommended max no load rpm is meaningless then as a comparison.

:agree2:

Max power means max heat....knock it back a touch.