Chainsaw Repair
Husqvarna - Stihl - Poulan - Jonsered - Dolmar chainsaws and more => Chainsaws not listed - Gas OPE => Topic started by: trappermike on December 29, 2018, 01:39:11 pm
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I have an old Chainsaw Repair Manual that covers many old saws,including the 275/276 and 3980/390. I noticed in the tune-up section for these saws that ignition timing was supposed to be set at 35 degrees,this is far more ignition advance than I've ever seen on any 2-stroke,and any 2-stroke that is advanced too far the piston can overheat and seize. I think I finally figured out the answer- those saws were run at 16-1 gas-oil mix using #40 motor oil,an incredibly "Thick" fuel/oil mix,with that much oil in the fuel the burning rate would be slowed down a lot,making a lot of extra ignition advance needed.
Here's the catch-if you leave the timing as original and now burn a 50-1 mix with modern 2-stroke oil,this is going to burn far faster than the original 16-1 sludge,making the timing too advanced for modern faster burning fuel mixes,possibly overheating or seizing the piston.To counter this I would suggest retarding the timing to about 30 degrees and/or using only the best Premium fuel. The ignition advance on most modern 2-strokes is often between 24-28 degrees.
I just don't want to see someone restore and get running one of these old models(with no spare pistons available) only to have the piston fatally seize,that would be a shame!
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Many older saws used more advance