Boertjie
ArboristSite Lurker
Hi guys. I'm in the process of building a Dolmar 85cc bigbore race saw and got stuck on the tuned pipe. Slapping on a pipe from a different saw (73CC) it ran well with lots of torque. Free running revs are 12800 and dropping to 11200 in the wood. I pulled the cylinder and remapped the porting done to design a pipe for it with 2 stroke wizzard. Pipe build and fitted the free running went up to 14500 rpm and now doing 12800 in the wood.
As soon as I hit 12000 free running ans above the machine sounds like its hitting its rev limiter and develop a serious miss. Which all goes away once its under load in the wood.
I know the problem is the pipe but where to look? Do I need to increase its header lenght? Increase its diameter?
Why does it behave like it does with this particular pipe thars designed for it?
Donor chassis a Dolmar PS7900, Husky 272 unlimited coil, Tilly 296 carb from a Dolmar 133, NWP big bore cylinder, timing advanced 30 degrees
As soon as I hit 12000 free running ans above the machine sounds like its hitting its rev limiter and develop a serious miss. Which all goes away once its under load in the wood.
I know the problem is the pipe but where to look? Do I need to increase its header lenght? Increase its diameter?
Why does it behave like it does with this particular pipe thars designed for it?
Donor chassis a Dolmar PS7900, Husky 272 unlimited coil, Tilly 296 carb from a Dolmar 133, NWP big bore cylinder, timing advanced 30 degrees