Chainsaw Repair

then put a wider skirted piston in it , remember some saws have a real wide skirt piston in them at these GTG's so pretty much a real racesaw , if you use the stock piston get the compression up as high as you can as that helps the 7900 alot and the higher compression works very good with the tight crankcase volume , if you raise your transfer ports to high it will boil the gas in the crankcase real bad and have less power so watch how high you raise them

I have done alot of 7900's , 99% were worksaws but have built a couple race 7900's on alcohol , on muffler or pipe , Myself I would use the 272 piston as its a single ring , I have made my own 7900 wide skirt pistons but that takes me alot of time , now you will have to build a spacer plate which I know is nothing for you cause the 272 piston is taller than the 7900 piston but also with using the 272 piston you donot need to grind your crankcase as much as with a 7900 wide skirt  piston cause the skirts hit the crankcase at BDC,

No secret on the coil , its a 272 coil and retime the flywheel, , the easiest way for me to tell you how to time the coil to the flywheel is find someone that will let you time a stock 272 , Get a dial gauge in your sparkplug hole , find TDC and look at where the coil matches the flywheel magnets , transfer the coil over and start your motor at TDC and mount the flywheel to the same spot of the magnet or you can go advance the flywheel a touch over the stock 272 setup, I know most transfer the coil onto the 7900 metal part but I just use the 272 coil setup and make the holes line up

My second post & already lovein this site.  Thanks Ed for letting out some of the secrets of the 7900.
I think I may be gitting a 6400 in on trade in the near future that I'll do some playin with. 
I've learned alot in just a few minutes from this thread.  Thanks fellers


fixed it for you 

That's a first 

I just bought a 7900 basket case, so I'll be watching this thread closely. Ed. When you say get the compression up as high as you can. Were talkin what? 175+?