ryskie22 Posted October 13, 2009 Report Share Posted October 13, 2009 need some help here guys got a 421 cub on gas with 39 keihin pwks, trying to get a starting point for jetting.I ride at sealeval to 500 feet at the coast,got a 160 main and a 52 pilot now what do you think! I did search a little before i posted and it seems everybody has 35s. Quote Link to comment Share on other sites More sharing options...
dutch350 Posted October 13, 2009 Report Share Posted October 13, 2009 I have 162 mains 48 pilot cel needle middle clip. thats at sea level, 421 cub & 39 pwk's. Quote Link to comment Share on other sites More sharing options...
ryskie22 Posted October 13, 2009 Author Report Share Posted October 13, 2009 I have 162 mains 48 pilot cel needle middle clip. thats at sea level, 421 cub & 39 pwk's. do you think 160 main might be to lean? Quote Link to comment Share on other sites More sharing options...
captainhowdie Posted October 13, 2009 Report Share Posted October 13, 2009 Im running 175 main, 55 pilot, 1 1/2 turns out, needle on the 4th clip. But its only about 45 degrees here right now. Im at sea level also. Quote Link to comment Share on other sites More sharing options...
dajogejr Posted October 15, 2009 Report Share Posted October 15, 2009 I've found the jetting between 35PWKs and 39s doesn't differ very much on the same motor. 48 pilots, CEL needle, 152 mains to start you off. That's if you're less than 1000 feet ASL and normal riding temps....60's to 80s. You're fat right now on your jetting...but I bet once it starts revving out it pulls nice...it'll pull cleaner once you clean up the jetting. Quote Link to comment Share on other sites More sharing options...
ryskie22 Posted October 16, 2009 Author Report Share Posted October 16, 2009 I've found the jetting between 35PWKs and 39s doesn't differ very much on the same motor. 48 pilots, CEL needle, 152 mains to start you off. That's if you're less than 1000 feet ASL and normal riding temps....60's to 80s. You're fat right now on your jetting...but I bet once it starts revving out it pulls nice...it'll pull cleaner once you clean up the jetting. funny you say that 35s and 39s dont differ much on jetting on the same motor, i had 35s before with the same jets and it seemed you had to rev it hard before you launched or it would bog, only when the sand was heavier and it would not like to roll on the throttle very well it would sputter out the pipes and the more throttle you gave it the worse it got,now you could always clutch it and it would be gone. never tried to figure out if it was lean or rich? only ran them a season and put 39s on her,so i may still have that same problem? my 35s i think were good on main jet,i warmed her up at the beach on a 80 degree day and put two new plugs in her and made a pass up to 5th gear and shut her down,pulled the plugs cut them and had just a hair over a 2 millimeter brown ring. thanks for the info Quote Link to comment Share on other sites More sharing options...
Hilarious Posted October 16, 2009 Report Share Posted October 16, 2009 (edited) i have 175 mains, 52 pilots, CEL needles on middle clip, (2) turns out on air screws. runs like an ethiopian chasing a donut that's rolling down a hill. i think all of our motors are the same but different. lol Edited October 16, 2009 by Hilarious Quote Link to comment Share on other sites More sharing options...
KEVSWS6 Posted October 16, 2009 Report Share Posted October 16, 2009 Hilarious runs the same as I run my personal bikes. Deep sand on play bikes that see a lot of wide open throttle. Sucks gas like a fat girl inhales cake. Quote Link to comment Share on other sites More sharing options...
KEVSWS6 Posted October 16, 2009 Report Share Posted October 16, 2009 I've found the jetting between 35PWKs and 39s doesn't differ very much on the same motor. 48 pilots, CEL needle, 152 mains to start you off. That's if you're less than 1000 feet ASL and normal riding temps....60's to 80s. You're fat right now on your jetting...but I bet once it starts revving out it pulls nice...it'll pull cleaner once you clean up the jetting. I cant run a 421 drag ported this lean. I have tried. Locked up two 421's running 162 and 165 mains. Even went to the dyno and tried it and after four pulls the exhaust temps got out of control. I always end up at 175 to 180 mains CEG needle middle clip and 50 to 52 pilots. Now I might do it different. Play bikes get multiple pulls back to back. Have to make sure the motor will not overheat. I notice that one to three pulls is fine. Temps look great on the exhaust and water. Nice HP numbers. Do a few more pulls and the exhaust gas temps get out of control. I have found that you cant keep the bike cool if you don't have enough gas going in. Even if your cooling system is top notch with big RAD, ice and over sized impeller. The piston gets hot to fast and you have a soft seize. It usually unlocks after a few minutes and you can even start and ride it again. Power will be down and you will do it again. Big jets in drag/dune cubs seems to have cured my problems. Quote Link to comment Share on other sites More sharing options...
00tbanshee Posted October 16, 2009 Report Share Posted October 16, 2009 with a non ported or just a mild cleanup cub you can get away with 165 mains,but once you get someone like kev to port a set your going to be up close to 180.trust me, i know first hand! Quote Link to comment Share on other sites More sharing options...
Hilarious Posted October 16, 2009 Report Share Posted October 16, 2009 (edited) i forgot to mention my cub was drag ported. Jeff knows his shit on these motors too. Edited October 16, 2009 by Hilarious Quote Link to comment Share on other sites More sharing options...
FASTOYS Posted October 17, 2009 Report Share Posted October 17, 2009 Thanks Hilarious, we try! Dajogejr, motors would get burnt down around here with the jetting specs your saying. Our findings are right inline with Kevins as we are at 1400 ft and run 172-175 range on most w/39s, and at sea level or longer runs we run 180 -185 range. In my experience, if the Drag porting flows efficiently enough it doesnt seem to change jetting on Cubs more than a jet size or 2. Ryskie22, in the end I recommend you ask whoever you bought the cubs from or your builder as they should know or they shouldnt be selling/installing them because as you see, on the internet you will get several answers and some could cost you alot more money than others! Quote Link to comment Share on other sites More sharing options...
dajogejr Posted October 18, 2009 Report Share Posted October 18, 2009 As said, we can only give you a baseline...final tune is on you. I ran that jetting for a year, even some cold weather. The cub was from FAST cleaned up. I hotlapped it at the track, through the dunes, etc. Never had an issue with them...and sold them at the end of the season in perfect shape. We're lower elevation as well... Quote Link to comment Share on other sites More sharing options...
ryskie22 Posted October 18, 2009 Author Report Share Posted October 18, 2009 thanks for all the replies, sounds like i need to make some runs and check my egts real close and go from there. i might re dyno with the 39s at the end of the year, i will no then were my jetting will wnd up. just was going to ride it one last time before winter realy gets here to see if there will be any other issues before the dyno, gotta get the kinks worked out! Quote Link to comment Share on other sites More sharing options...
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