jeepman128 Posted February 1, 2007 Report Posted February 1, 2007 OK... I have a 421 cub with 145psi in each cylnder (21cc) domes. I just installed SoCallinit's 36mm airstrykers on my bike and it will not launch in 2nd for the life of me. (1st gear is just fine) Bansheeman and Polish have both ridden the bike and know exactly what I am talking about. I have had the single carb set up on it with both a 35mm and 38mm and now the duals but it will not launch in second with any of the set-ups. It has the stock gearing (14-41) and 8paddle haulers. I had it dyno tuned in the Glamis flats so I am sure the jetting is spot on. But something just isn't right with the bike. It runs perfect otherwise, (doesn't bog, or miss) but it just doesn't have enough gut power to launch in second that I would think a cub would have. Could this be because of the domes and not running that much of compression or timing (+4) with a cub??? And I am guessing something else might be wrong because it only dyno'd 75hp... but there are no other signs of it running bad, in fact I think it makes a perfect pump gas running dune bike! I just keep losing races because the darn thing won't launch in second! I mean correct me if I am wrong but most cubs are making that kind of power with stock carbs and Toomy's. I have 36mm AirStrykers and a set of Cpi's.. Any ideas? Quote
djackbanshee Posted February 1, 2007 Report Posted February 1, 2007 My opinion would be carbs are too big, lack of bottom end go with 30 or 33 pwk carbs Quote
locogato11283 Posted February 1, 2007 Report Posted February 1, 2007 carbs arent your problem. you can run 39mm pwk on that and it should still haul the mail and be plenty of power to take out in 2nd. are you sure the jetting is right on? 145 psi isnt much compression for a cub motor. you could be losing some low end power there. our cub bikes are at around 170 psi... Quote
BigRed350x Posted February 1, 2007 Report Posted February 1, 2007 I had my 4mil cub up over 200psi a few times with timing up above 7 Quote
bada450r Posted February 1, 2007 Report Posted February 1, 2007 OK... I have a 421 cub with 145psi in each cylnder (21cc) domes. I just installed SoCallinit's 36mm airstrykers on my bike and it will not launch in 2nd for the life of me. (1st gear is just fine) Bansheeman and Polish have both ridden the bike and know exactly what I am talking about. I have had the single carb set up on it with both a 35mm and 38mm and now the duals but it will not launch in second with any of the set-ups. It has the stock gearing (14-41) and 8paddle haulers. I had it dyno tuned in the Glamis flats so I am sure the jetting is spot on. But something just isn't right with the bike. It runs perfect otherwise, (doesn't bog, or miss) but it just doesn't have enough gut power to launch in second that I would think a cub would have. Could this be because of the domes and not running that much of compression or timing (+4) with a cub??? And I am guessing something else might be wrong because it only dyno'd 75hp... but there are no other signs of it running bad, in fact I think it makes a perfect pump gas running dune bike! I just keep losing races because the darn thing won't launch in second! I mean correct me if I am wrong but most cubs are making that kind of power with stock carbs and Toomy's. I have 36mm AirStrykers and a set of Cpi's..Any ideas? when i race i keep the rpm range as high as it will let me,if not it will fall on its face.....i think its all on take off,iam also geared way higher than you,and i have 165 lb per cylinder.iam geared 15/43 for the hill,i think it should take of in 2nd gear ,practice my young grass hoper. :: :: :: :biggrin: Quote
Animalman294 Posted February 1, 2007 Report Posted February 1, 2007 Yeah, with that motor you should be around 180-185 psi, but to get there you need to take the timing to at least +7 and the domes should be down around 18-19cc. And once you get the compression up you definately need to run race gas, or you wont have that motor for very long.............. :thumbsup: Quote
[email protected] Posted February 1, 2007 Report Posted February 1, 2007 7 or 10 on the timing and bump that compression up to around 180ish get yourself some bad ass gass , strap yourself on to the seat and Look back as you roost your competition Im 10' timing , 190psi , 38mm carbs , 16,40 gearing and i can spin 2nd on the asphalt VEEEEERY EASY ... Quote
dajogejr Posted February 1, 2007 Report Posted February 1, 2007 Ran my 421 with shearers and 35PWKs, 185PSI...8 degrees on my plate and my dyna on curve 3, the most advanced. With stock gearing, 10 paddle haulers on a 6 over arm, mine launched in 2nd all day long without any issue. I agree...lower than 6K RPM, you're not making power....and if you fall off that power...it takes a sec for you to get back in the pipe on that motor. Here's my bike as said, launching in second...that's me in the far lane, with my 245 lb fat ass not to mention. And this was some thick, wet ass heavy sand, too.... http://video.google.com/videoplay?docid=6136815352508756093 Quote
jankab Posted February 1, 2007 Report Posted February 1, 2007 OK... I have a 421 cub with 145psi in each cylnder (21cc) domes. I just installed SoCallinit's 36mm airstrykers on my bike and it will not launch in 2nd for the life of me. (1st gear is just fine) Bansheeman and Polish have both ridden the bike and know exactly what I am talking about. I have had the single carb set up on it with both a 35mm and 38mm and now the duals but it will not launch in second with any of the set-ups. It has the stock gearing (14-41) and 8paddle haulers. I had it dyno tuned in the Glamis flats so I am sure the jetting is spot on. But something just isn't right with the bike. It runs perfect otherwise, (doesn't bog, or miss) but it just doesn't have enough gut power to launch in second that I would think a cub would have. Could this be because of the domes and not running that much of compression or timing (+4) with a cub??? And I am guessing something else might be wrong because it only dyno'd 75hp... but there are no other signs of it running bad, in fact I think it makes a perfect pump gas running dune bike! I just keep losing races because the darn thing won't launch in second! I mean correct me if I am wrong but most cubs are making that kind of power with stock carbs and Toomy's. I have 36mm AirStrykers and a set of Cpi's..Any ideas? With your compression that low, give it some timing it will help Quote
No Limit Powersports Posted February 1, 2007 Report Posted February 1, 2007 (edited) To start with a cub likes compression and timing so i would start there. Measure your squish before you just go throwing some smaller domes in it. You are going to have to get the squish where it needs to be before it will run right, personally i would run it between .036-.045 but some may disagree. I have seen pump gas 421 cubs that acted this exact same way and the problem was they were running a squish of about .060 and 19cc domes with about 145lbs, but the problem can come from many different things, did anybody port this cub, are you sure on the jetting, timing, compression ect... To be honest I think a 421 cub should be running 180+ compression with at least +7* of timing and good gas...otherwise what you could have just built a 350 stock cylinder for a lot cheaper and made 75hp...imo... Edited February 1, 2007 by bansheestang Quote
dajogejr Posted February 1, 2007 Report Posted February 1, 2007 To start with a cub likes compression and timing so i would start there. Measure your squish before you just go throwing some smaller domes in it. You are going to have to get the squish where it needs to be before it will run right, personally i would run it between .036-.045 but some may disagree. I have seen pump gas 421 cubs that acted this exact same way and the problem was they were running a squish of about .060 and 19cc domes with about 145lbs, but the problem can come from many different things, did anybody port this cub, are you sure on the jetting, timing, compression ect... To be honest I think a 421 cub should be running 180+ compression with at least +7* of timing and good gas...otherwise what you could have just built a 350 stock cylinder for a lot cheaper and made 75hp...imo... I agree 100%. jankab did my cub for me after all the problems I had initially with it. A dip in the deck was leaking coolant, the base of it leaked....etc. I was miserable. He got done flattening and sealing it up, and my dumb ass took it out on long trail rides, lost an air filter, sucked water...and popped a head gasket again. Took it back, fixed it again...and it ripped all year at the track and dunes. Trust me...you've got a good package started. get the compression and timing up...and you'll be amazed how good that little motor will run! Second gear holeshots all day long... Quote
wesw Posted February 2, 2007 Report Posted February 2, 2007 just for shits and giggle what is your jetting. pilot, needle, clip, mains. what size of tires are you running. Quote
lowriderb Posted February 2, 2007 Report Posted February 2, 2007 for maybe running lower compression and timing, you could just try launching in 1st... 2nd gear doesnt always work out for every situation and if you dont adapt to the conditions then you wont win races.. also depending on the gearing, tire size, your weight, swing arm (for spin) ect.. different gears would be better.. if i remember right my 421 was running 180-190psi of compression, the timing was on 9 or 10 at the plate with the stock cdi.. the squish was a little tighter than .036 but i dont remember exactly what it was.. the motor liked the 38's i had on it as well and im sure if i geared it different i could have launched in 2nd with 22in tires.. Quote
wesw Posted February 3, 2007 Report Posted February 3, 2007 any new stuff. what is your jetting?? Quote
Animalman294 Posted February 3, 2007 Report Posted February 3, 2007 Ok, what happened, any improvements..................? Quote
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