Coil mounted on jug, kind of odd. Stock comp, saw had like 2 tanks through when I got it. Cut the base, .035 witch is just a bit much, free ports just a bit .003-5 Cut the squish ended up a bit loose at .026 ish but couldn't drop the jug anymore cause of the free porting.
Ported same bar/chain the log was a bit bigger by the time I shot this vid, the saw didn't gain a lot of speed, as the coil was holding me back set at 12,800/900 and coil would kick in round 13,100 This saw gained a ton of use able torque from stock, didn't have to nurse it through bar buried/noodle cuts like when stock. Figure this is the size wood the saw was designed for might as well see how it does. The real small stick cutting was to show the throttle response, simulate a limbing scenario.
Nice work Red97. I really enjoy this type of thread. I have been messing around with porting and going to make a mandrel to work on the lathe. What does free porting mean.
Thank you This dolmar has a Short skirt piston. Free port is when the piston is at top dead center, and the skirt dosent completely cover the bottom edge of the exhaust port. Let's the charge in the case escape out the exhaust. Instead of going up the transfers and into the chamber to be burnt.
Thanks I get it. I guess that's why some use epoxy in ports to seal it off? How do you decide where you want port timing when to change it or return to stock numbers after cutting the base and squish.
Never seen epoxy in an exhaust port (heat). Most of the time epoxy is used to fill the intake port. I have only ported 5/6 saws. This is my (cliff note approach) Saw all stock check squish, and port timings, set piston at TDC and scribe the bottom through the ex port. Pull the jug Measure from the scribed line to the bottom of the piston skirt, that tells you how much you can take off the base before the saw free ports. As for the port timing, that just depends what you want out of the saw. With this dolmar, it has a limited coil 13,100 in my case, and a small carb. No sense trying to make a high rpm screamer. So I bumped the comp, and Tryed to broaden the torque curve. Raised the ex in attempt to raise the hp a bit higher in the band. Just dropping the jug, setting squish and widening/shaping the ports can net decent gains.
Yes I ment in the intake port I would think only weld would work in the exhaust if needed. I have messed with alot of engines both 2 and 4 stroke growing up and trying stuff. Now that I'm older I want to understand the science of what is going on instead of just trying stuff. Thanks so much for your time and knowledge I really appreciate it.
The had thing with saws, it pretty much none of the 2 stroke info published crosses over. Lots of ideas but only way to tell is actually try them. I am gathering material to build a saw dyno. Just so I can bet a stock base line then test mods along the way.
Love my 421. My go to saw. I rarely pick up the 026 anymore. Between the 421 and the dolkita 6421 i couldn't be happier for firewood work. Some day I'd like to try a ported 421. Enjoyed your thread.
