McCulloch Super Pro 125c build thread

[Bigmac]

My understanding is that the big aftermarket kart stuffer moves the power up in the rpm, with a loss of low end, and is undesirable in a saw.

 

[sawfun]

My understanding is that the big aftermarket kart stuffer moves the power up in the rpm, with a loss of low end, and is undesirable in a saw.

I believe the full circle cranks aren't as desirable in a saw either as they help with rpm gain (horsepower) but likely not torque. In a cart, rpm changes frequently where a saw is generally kept at max rpm. The saw generally is fine running on the top end as long as torque doesn't suffer, which I fear, is the case with regards to full circle or stuffers in the crankcase.

 

[jacob j.]

What the kart guys generally want is acceleration. They want to move from mid-range RPM to high as they're coming out of a corner or a curve
and then max out as they're coming down a straight away. The full circle cranks and "Super Stuffers" help with that. They're also usually running
as much carburetion as they can, a lot more than what's going to be available to the saw motors.

 

[p61 western]

My understanding is that the big aftermarket kart stuffer moves the power up in the rpm, with a loss of low end, and is undesirable in a saw.

I believe the full circle cranks aren't as desirable in a saw either as they help with rpm gain (horsepower) but likely not torque. In a cart, rpm changes frequently where a saw is generally kept at max rpm. The saw generally is fine running on the top end as long as torque doesn't suffer, which I fear, is the case with regards to full circle or stuffers in the crankcase.

What the kart guys generally want is acceleration. They want to move from mid-range RPM to high as they're coming out of a corner or a curve
and then max out as they're coming down a straight away. The full circle cranks and "Super Stuffers" help with that. They're also usually running
as much carburetion as they can, a lot more than what's going to be available to the saw motors.

Great input guys. The more info the better in this thread. What about the boost ports?

 

[Bigmac]

I think adding the boost port would be cool, might help a little bit with Power, would be like the 797, even if you ran the standard CP piston, It would feed port through the wrist pin hole,but a kart piston would flow better. the CP didn’t come that way so I wouldn’t worry about it though either.What do you guys think? Do you think the Boost port is what helps the 797 feel stronger

 

[WOODS]

That sucks, did terry rebuild the rod install the piston or did someone else?

Someone else. I didn’t have a new piston or pin or rod. We just freshened it up with new bearings as it would bind when you rotated the crank. Made 196# before we began. Also put new rings in it but disaster struck before we planned to measured the compression as rebuilt. With a big carb, I am sure it would have been a hot rod.

Ron

 

[sawfun]

I think adding the boost port would be cool, might help a little bit with Power, would be like the 797, even if you ran the standard CP piston, It would feed port through the wrist pin hole,but a kart piston would flow better. the CP didn’t come that way so I wouldn’t worry about it though either.What do you guys think? Do you think the Boost port is what helps the 797 feel stronger

I found the regular 797 to be strong in the torque area, like geardrive type torque, but not as high an rpm saw as the super 797 or cp125. Just yesterday I finally, after over a year of it on my bench, finished putting the gear drive on a PNW barn find 797. I had run this saw as a direct drive and thought it strong. I thought why not more of a good thing, especially for the 72" Cannon it. Sorry for the incorrect direct drive pictures.

 

[sawfun]

This saw hadn't been run in over 2 years and fired on the first half of the first pull on a prime.

 

[p61 western]

View attachment 174313
This saw hadn't been run in over 2 years and fired on the first half of the first pull on a prime.

Very cool that you got it going now. What's your thoughts on the boost ports being added to the cp125 block like on the 797?

 

[sawfun]

Very cool that you got it going now. What's your thoughts on the boost ports being added to the cp125 block like on the 797?

I couldn't say on the effect of boost ports as there is supposed to be 5 different versions of the standard 797, each with different porting numbers, with the earlier, the more aggressive. The 797 super is said to be like a cp125 as far as porting. I agree they feel the same as far as performance goes, I like 125's as they are, if you want boost ports, get a 101 IMHO.

 

[sawfun]

I would like to run that 797g against a stock 137cc 090g both with 72" bars buried in some Doug Fir. Those big 090g's are truly a long bar force to be reckoned with. This would definitely be one man geardrive titan match.

 

[Bigmac]

I would like to run that 797g against a stock 137cc 090g both with 72" bars buried in some Doug Fir. Those big 090g's are truly a long bar force to be reckoned with. This would definitely be one man geardrive titan match.

I have a stock 090g with 137cc top end, but no 72” bar! Lol

 

[sawfun]

I have a stock 090g with 137cc top end, but no 72” bar! Lol

My 090g is ported so that won't be a fair fight at all. I know a stock 137cc 090g with 72" bar doesn't really even work. It kinda runs like there is no bar on it at all. If there is a PMW GTG at Farleyville this June, and you can attend, maybe we can have that long bar shootout. I can supply a 72" bar for you to use.

 

[Bigmac]

My 090g is ported so that won't be a fair fight at all. I know a stock 137cc 090g with 72" bar doesn't really even work. It kinda runs like there is no bar on it at all. If there is a PMW GTG at Farleyville this June, and you can attend, maybe we can have that long bar shootout. I can supply a 72" bar for you to use.

Was hoping to make it last year, but it didn’t work out, hopefully this year! That would be fun!

 

[sawfun]

797g running strong with 72" and little, if you can call it that, brother 895, just out of the rafters with 60" bar.

 

[Canadian farm boy]

797g running strong with 72" and little, if you can call it that, brother 895, just out of the rafters with 60" bar.
View attachment 174450 View attachment 174451 View attachment 174452

Couple mean looking monsters there. Very nice.

 

[p61 western]

Got the CP block yesterday, and it looks great. Cleaned up the crank some, and started on the stuffer.

 

[p61 western]

If anyone knows how to decode the numbers on the block that would be cool.

 

[Lee H]

797g running strong with 72" and little, if you can call it that, brother 895, just out of the rafters with 60" bar.
View attachment 174450 View attachment 174451 View attachment 174452

Hard to beat a 797G. I love the few I have built.

 

[Al Smith]

Just general info .On the kart engines on an oval track they wanted the engine to hit max RPM's just prior to braking for the curve .Of course that depended on the track size .On a road course they tried for mid range because the straight of ways were generally short .It was a matter of the gearing and the porting plus they might have half a dozen different engines back in the day .It wasn't one size fits all . On a chainsaw you have two speeds,idle and WOT .