Cubshee421 Posted December 14, 2014 Report Share Posted December 14, 2014 I have a 421 cub that had big bore shearer pipes on it. It ran pretty tall gearing with these pipes but if you had to lift off the throttle it would just bog out. Now I have small bores but it seems like it dont have the power to pull long gearing any more but its more forgiving if you let off throttle. So what are your guys thoughts on this, plugs are very clean with the small bores idk if I may be too lean on mains now. Quote Link to comment Share on other sites More sharing options...
dave5.0 Posted December 14, 2014 Report Share Posted December 14, 2014 Curious to hear myself. Quote Link to comment Share on other sites More sharing options...
camatv Posted December 14, 2014 Report Share Posted December 14, 2014 if its a high port cub. its going to fall off the pipe no matter what. loose weight on the bike or rotating mass on driveline. the big bore's helped the pull down low and masked some of the lack of lower rpm power. ( 6500-7500) the smalls dont have as much emphasis on the lower rpms but probably are helping up top a tad bit more.. or your overall setup is a lil off.. domes , real porting ,may help? depends on the build of the motor. Quote Link to comment Share on other sites More sharing options...
possum Posted December 14, 2014 Report Share Posted December 14, 2014 might wanna check your timing. Quote Link to comment Share on other sites More sharing options...
5150banshee Posted December 14, 2014 Report Share Posted December 14, 2014 might wanna check your timing.This Quote Link to comment Share on other sites More sharing options...
Cubshee421 Posted December 14, 2014 Author Report Share Posted December 14, 2014 Timing is at plus 7 Quote Link to comment Share on other sites More sharing options...
5150banshee Posted December 14, 2014 Report Share Posted December 14, 2014 Carb size and jetting ? Quote Link to comment Share on other sites More sharing options...
Cubshee421 Posted December 14, 2014 Author Report Share Posted December 14, 2014 Pwk 39s 48 pilots 158 mains av100ll gas Quote Link to comment Share on other sites More sharing options...
5150banshee Posted December 14, 2014 Report Share Posted December 14, 2014 Not sure where ur located, I'm in socal and that's lean for us I have same set up 39 pwk cub and sb shearer and I'm at 175,60 before dyno I imagine I'll drop 2 or more on main and maybe 1 on pilot and I'm only 6 degrees on timing and also running 110 with 19 cc domes and the super thin base gasket. Quote Link to comment Share on other sites More sharing options...
possum Posted December 15, 2014 Report Share Posted December 15, 2014 (edited) well with switching pipes you might wanna check jetting again. It coukd just be lean. Feed ut fuel And back the timing to 5 and see how it responds. check squish, compression, while your at it. Edited December 15, 2014 by possum 2 Quote Link to comment Share on other sites More sharing options...
registered user Posted December 15, 2014 Report Share Posted December 15, 2014 probly some genius sky jacked the exh port Quote Link to comment Share on other sites More sharing options...
BANSHEEBEEFM2M Posted December 15, 2014 Report Share Posted December 15, 2014 Did you rejet after you changed pipes maine Quote Link to comment Share on other sites More sharing options...
Cubshee421 Posted December 15, 2014 Author Report Share Posted December 15, 2014 Big bore pipes pulled 17-42 2nd gear launch with 160 main jets at 4 degree timing. Now small bores with 15-42 2nd gear launch 158 mains at 7 degrees seems like it should be easy to pull. It will pull hard first 2 passes then it does a weird bog when dumping the clutch after that. Im going to check for a broken reed tomorrow Quote Link to comment Share on other sites More sharing options...
sprinklerman Posted December 15, 2014 Report Share Posted December 15, 2014 Heat soak . 1 Quote Link to comment Share on other sites More sharing options...
Cubshee421 Posted December 15, 2014 Author Report Share Posted December 15, 2014 Heat soak .please explain I want to learn Quote Link to comment Share on other sites More sharing options...
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