ericm979
Super Member
- Joined
- Nov 25, 2016
- Messages
- 5,822
- Location
- Santa Cruz Mountains CA, Southern OR
- Tractor
- Branson 3725H Deere 5105
Octane is a measure of detonation resistance. Higher octane fuel has slightly less energy (we're talking pump gas here, race fuel can have different things in it). High octane does not make more power but it allows a higher compression ratio before detonation, and that makes more power. Detonation seizes two strokes quickly. Unlike four strokes you often don't hear it.
Richening the oil mixture leans out the fuel:air mixture. The carb is metering mixed oil and gas- it delivers a fixed amount of oil+gas per unit of air. But oil is not gas and does not count for the fuel:air ratio. However the difference in air/fuel ratio from 50:1 to 32:1 is small. Maybe if the saw was already running lean that'd make it too lean.
Echos tend to come set lean from the factory, more than Stihls. On my CS352 I gutted the cat and pulled the limiter caps so I could retune the carb. There wasn't a performance gain from gutting the cat but I left the rest of the muffler intact. This is a brush cutting saw and being quiet is more important than power. Removing the cat should make it run cooler though. Heat kills two strokes too. The 352's air filter lets fine material through. It's an old school material where the newer Stihls have better filter material. I use oiled foam filter material in the air box where the largest holes are to trap some of the fines. The gas and oil fillers are small so it's easy to overflow. OTOH it's super light, handles well and starts incredibly easy.
Richening the oil mixture leans out the fuel:air mixture. The carb is metering mixed oil and gas- it delivers a fixed amount of oil+gas per unit of air. But oil is not gas and does not count for the fuel:air ratio. However the difference in air/fuel ratio from 50:1 to 32:1 is small. Maybe if the saw was already running lean that'd make it too lean.
Echos tend to come set lean from the factory, more than Stihls. On my CS352 I gutted the cat and pulled the limiter caps so I could retune the carb. There wasn't a performance gain from gutting the cat but I left the rest of the muffler intact. This is a brush cutting saw and being quiet is more important than power. Removing the cat should make it run cooler though. Heat kills two strokes too. The 352's air filter lets fine material through. It's an old school material where the newer Stihls have better filter material. I use oiled foam filter material in the air box where the largest holes are to trap some of the fines. The gas and oil fillers are small so it's easy to overflow. OTOH it's super light, handles well and starts incredibly easy.