astewart Posted January 19, 2013 Report Posted January 19, 2013 Just built a 421 4mill it is either all or nothing has no bottom end! If you try to take off has no power unless you rev up and dump the clutch. It has PJ34mm carbs that I bought used. Any ideas? Could it be 2 big of jets? Sent from my Desire HD using Tapatalk 2 Quote
dirtydownunder Posted January 19, 2013 Report Posted January 19, 2013 whats your setup, what jets you running. ? Quote
wfobasheeboy Posted January 19, 2013 Report Posted January 19, 2013 We are going to need more info. Pipe, timing , jetting, if you are at sea level or not. Then we can start to help you out. By the way welcome to HQ! Quote
BigRed350x Posted January 19, 2013 Report Posted January 19, 2013 How much compression you have? Compression ratio? Squish clearance? Timing? Ported at all? If you have a good quality drag port on top of the factory castings, there may not be much you can really do. Bump timing up, raise compression, Nd some tuning. If you are after some good low end grunt and midrange, sell the cub and try to get a serval or a small-block twister, or even a set of dune or mx port stock cylinders. -jared Quote
astewart Posted January 19, 2013 Author Report Posted January 19, 2013 Not sure on jets, has 4 degrees timing advance Sent from my Desire HD using Tapatalk 2 Quote
astewart Posted January 19, 2013 Author Report Posted January 19, 2013 Cpi outframe drag pipes, elevation is 954ft in Oklahoma, not sure on jets, 4 deg advance timing key, the cylinders are Siamese 68mm 421cc +4mm 4 Mil Serval Cub Top end Sent from my Desire HD using Tapatalk 2 Quote
bansheefromhell Posted January 20, 2013 Report Posted January 20, 2013 you're not hitting the throttle hard enough... Quote
crazycracker520 Posted January 20, 2013 Report Posted January 20, 2013 I'm gna say carbs. crazycracker Quote
trickedcarbine Posted January 20, 2013 Report Posted January 20, 2013 I'm gna say carbs.crazycracker Negative ghost rider. You are so wrong. Those 34's are just fine on that motor. Quote
trickedcarbine Posted January 20, 2013 Report Posted January 20, 2013 Cpi outframe drag pipes, elevation is 954ft in Oklahoma, not sure on jets, 4 deg advance timing key, the cylinders are Siamese 68mm 421cc +4mm 4 Mil Serval Cub Top end Sent from my Desire HD using Tapatalk 2 You are positive that you were given a "Serval" cylinder? You measured the port heights? Your original post just sounds typical of a regular Cub cylinder. But, it should have low end for sure if it is a Serval. I think you could be runnin the wrong pipes for starters. Are they small flange small bore? Also, take apart the carbs and let us know what jets you have. Pilot? Needle and clip position? And main jet? Also snap a pic of the spark plugs and use the mobile photo bucket app to upload the photos. Quote
astewart Posted January 20, 2013 Author Report Posted January 20, 2013 The guy I bought them from said they was big bore Sent from my Desire HD using Tapatalk 2 Quote
Sandking Posted January 20, 2013 Report Posted January 20, 2013 Find out what jets your running and check floats. Your running used carbs remember. Who knows whats in them you have to open them up. Quote
dirtydownunder Posted January 20, 2013 Report Posted January 20, 2013 you can find out if it is a serval by looking into one of the intake ports, there will be a SC marking on the roof of one, if its a serval. Quote
astewart Posted January 21, 2013 Author Report Posted January 21, 2013 Jets are160/55 in both carbs and it does say SC Quote
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