o0norton0o
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- Joined
- Apr 27, 2015
- Messages
- 1,740
comnoz said:
When I was a member of a dirt car pit crew, our pit neighbors tried every permutation of timing, fuel ratio, and plug to try to make more power in their race car. They ran their car so hot that when they came into the pits, one of their crew would mist their radiator with water to cool their engine off so it wouldn't burn up. Their premise for running their engine as hot as possible was the idea that "more heat is more power". My crew chief always shook his head at their antics because he knew they were going to burn their engine up eventually during one of their races. They weren't consistantly good racers, but I recall one night when they had it all working well and won their class (358 modified) that evening. (usually it's more how the car is set up to handle that makes you win, not making more power)
Knowing these pit neighbors was one of the reasons I've tried so many different jets, plugs, and timing positions on my commando... Long story short, my bike runs best on the factory recommended plugs, at the recommended timing, with the recommended jetting. For a while, I tried a richer jet and hotter plug. The only difference I noticed was the color of the insulator on my plug. I thought this extra fuel and hotter plug with a little more timing advance would make my engine a little more powerful, run a little cooler, and have a longer burn duration...
What it actually did was make the bike hard to start, color my plug insulator darker, and add no perceivable power. For a while I thought that the darker plug meant I was probably running at a lower temperature, so I had a safety margin against burning up my bike, but then I realized I also was using a hotter plug, so I theorized that there was probably no significant difference in temperature... and I was wasting my time.
I gave up trying to out think the engineers and went back to all stock recommendations (plugs, jets, timing) and everything runs well, and the plugs look clean. I'm sure there's another level of tuning that I could persue to make the bike run better (like measure and micro adjust the cam timeing) but I think for a stock motor with stock cam profile and stock carbs,.... stick with the stock specified settings.
The only effect a larger main jet had was I couldn't get my bike to go faster than 80mph. It would bog down when I gave it more throttle. This was my reason to go back to all the recommended parts and settings, and sure enough everything works better.
