421 cub small bore shearer vs big bore

[possum]

why did you run smaller jets with more timing?

[5150banshee]

why did you run smaller jets with more timing?

^^^^^ this,

when u advance ur timing the bike then runs hotter so you need yo go bigger on jetting, imo +7 is a little much and jetting is way off, bring the timing down to +4 and re jet. or make the process a hell of a lot easier pay the 160 bucks get a dyno tune on it. Where u located ??

[Cubshee421]

95380 im going back where I know the jetting is right and backing timing down to 4 it felt good there. Still going to double check reeds.

[5150banshee]

So yea with that zip your a little off on jetting and imo running way lean, bike is getting way hot and the 7 timing is making it worse. If your gunna leave those pipes on I'd start with a 170 main and 60 pilot and tune from there with timing 5.5,6 degrees.

[Cubshee421]

At 165 mains the plugs where black and wet going to start there.

[trickedcarbine]

please explain I want to learn

Guys who hot lap their motors will produce heat exponentially as each run is made. Heat soak refers to when the motor has been ran to the point that it is starting to produce so much heat that power begins to fall off. It creates a flat feeling up top in the rev. What's going on is that a motor is now creating more heat then the exhaust can move out of the motor. Typically motors up to 500 CC's will make their best power on small bore pipes. (This isn't always the case) However, just because a motor makes it's best power after one run on small bores, you create a whole new set of variables when you take that same combo and run it over and over. Especially on race fuel motors with a good amount of compression and timing. They make a considerable amount of heat. So, no real answer if you need Small or big bore. Kinda one of those things you gotta figure out through trial and error. I've seen guys run their bike on 300' sand on shearer small bores, out at the dunes that same motor rams better on the shearer big bores since it can get ran for about 5-10 runs back to back. There will be some variances in results between different pipe brands.

[Cubshee421]

I need to be able to run this bike at least 10 passes back to back. We just grudge race but I cant just run 1 or 2 passes. Timing back to 4 and some bigger maisn where installed now I just need some test hits.

[5150banshee]

Deep pockets I'm guessing hahahaha