sheeloco Posted June 25, 2011 Report Posted June 25, 2011 whats up guys. ive got a question, my brother just installled a 421 cub engine. went racing on dunes and im beating him every time. i have a 350 drag port job with cpi in-frames, 34 mikunis, 8 pdl haulers and he has the same setup except for the brand new cheetah cub. do you guys have any insights on this? p.s. all of our work has been done professionally by k&t performance. Quote
camatv Posted June 26, 2011 Report Posted June 26, 2011 i think i'd be calling K+T its not unheard of for a cub to loose to a SC bike.. but a properly built 421. hmm Quote
RadarRacing Posted June 26, 2011 Report Posted June 26, 2011 I dont know if you traded bikes to see if you can beat him on the other bike or not but if his bike is just slower than yours then the cub needs more tuning, timing, different domes, etc. Also jetting plays a big part in tuning, if you have a well tuned 80 or 90hp bike and his build is slightly off he will have less HP easily. 3 mainjets sizes too rich is 10-12hp less on a gas 421 even tho the plugs will look really close to perfect. Theres a big difference if a 90 HP cub is only making 75 or 80. Quote
locogato11283 Posted June 26, 2011 Report Posted June 26, 2011 Same tires? How hard is the Cub getting out of the hole? Quote
sandstalker Posted June 27, 2011 Report Posted June 27, 2011 I dont know if you traded bikes to see if you can beat him on the other bike or not but if his bike is just slower than yours then the cub needs more tuning, timing, different domes, etc. Also jetting plays a big part in tuning, if you have a well tuned 80 or 90hp bike and his build is slightly off he will have less HP easily. 3 mainjets sizes too rich is 10-12hp less on a gas 421 even tho the plugs will look really close to perfect. Theres a big difference if a 90 HP cub is only making 75 or 80. That is exactly right. I finished up a 4 mill cub motor on my bike last week and took it to a friend of mine to have it dyno tuned and i picked up 11hp by getting the jetting right,still a tad richer than we wanted but it is a alcohol setup and we wanted to be on the rich side. Also look at the weight of the bikes and what pipes is he using on his 4 mill setup? Quote
sheeloco Posted June 27, 2011 Author Report Posted June 27, 2011 i should have posted more on his ride: he's riding the 421, 34 mikunis, toomeys, 9 pdl haulers (newer and one more pdl than mine) weight wise i think our rides our close in weight. we'll continue working on his jetting and see if we can get it tuned in better and see what happens thanks guys Quote
J-Madd Posted June 27, 2011 Report Posted June 27, 2011 Put the CPIs on there. The Toomeys are killing it. It could probably use bigger carbs as well. I ran 39mm on mine on gas or alky. Quote
sandstalker Posted July 1, 2011 Report Posted July 1, 2011 Pipes are holding the motor back,i like shearer pipes but the CPI are nice also. If he changes the pipes he will most defenately need bigger carbs and probably already needs them. I run 41mm flat side mikuni's on mine but it is a alcohol setup but with the shearer out of frame pipes we ran the bowls dry and had to really jet it up to keep up with the pipes. Pipes,carbs and maybe step up the paddles but i would know doubt do the first two first. Quote
Sweet1 Posted July 17, 2011 Report Posted July 17, 2011 yea the pipes are no good on that motor Quote
BUILDER Posted July 18, 2011 Report Posted July 18, 2011 I also run a 421 cub with T5 pipes on it. When I first put it together I was not happy with how it preformed till I realized I wsa blowing the tires off it trying to launch it. My inital setup was not that great but after some tuning and spending some time with the bike it have gotten much faster. I would guess he is probably blowing the tires off 9 paddles on a 421 is not really enough tire if you are wanting to drag it and if the setup is not right a well built SC bike will take it no problem. I have since gone to shearers on mine and they do preform better but I think your setup is your biggest issue. Quote
Sweet1 Posted July 19, 2011 Report Posted July 19, 2011 very true, settup is huge you dont just throw a motor in a bike and have it be as fast as it can be, lockout,clutch,swingarm,gears,shocks.....RIDER(lol) all play a part in a fast bike Quote
421alkybanshee Posted July 19, 2011 Report Posted July 19, 2011 (edited) pipes and carbs are killing ya!!! Edited July 19, 2011 by 421alkybanshee Quote
yfzdunejumper Posted July 20, 2011 Report Posted July 20, 2011 i think i'd be calling K+T its not unheard of for a cub to loose to a SC bike.. but a properly built 421. hmm I think everyone is right but Cam has the best point. You are getting more than just motor work with K&T they will help you with your setup and make you as fast as possible. I know they will be happy to help you out. Quote
camatv Posted July 21, 2011 Report Posted July 21, 2011 exactilly. they can give you setup tips since they are the ones that built the motor. Quote
dcalsv02 Posted July 22, 2011 Report Posted July 22, 2011 I would get more paddles for that 421. 9 paddles are not enough. atleast 10 paddles. Quote
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.