Jred 920 super awakening

[Rx7man]

My buddy gave me 2 Jonsered 920's to fix into one.. The one was pretty busted up, but he said it made good power, the other was in better condition, but lacked oomph.
So starting with the busted up one, I took it apart and ported it out a little, matched up the miserable factory job on the piston windows to transfer ports and enlarged them a little.. then found the stock port timings and moved them around to 101/122/78, which is pretty mild, then did some muffler modding, removed the base gasket (thick bastard), and my squish was .45mm after that...

Could have used some new rings, they have a bit more end gap than ideal (.030"), but he was happy with the results on the test run.. he's going to cut a bunch of big trees this weekend and I'll see what he says about it.

I also fixed up his chain that was cutting crooked.. he forgot to file a few of the rakers on one side of it :banghead:

When I opened up the second saw, I found it was a standard 920, and the other was the 920 Super, which has drastically improved transfers which makes use of the piston windows and also along outside while the 920 standard only flows through the piston, which is pretty darned restrictive in stock form

 

[Rx7man]

Here's a comparison of the 920 jug on the left and the ported 920 super on the right



And the improved piston.



I know I could get more aggressive ports as well as timing numbers, but this is just a work saw... and it's hard to go back from too far