Ieat4strokes Posted March 13, 2012 Report Share Posted March 13, 2012 Just got a 421 cub together last night for a buddy of mine. Currently he has 34 PJ's, 160 mains and 55 pilots air screw .5 out at sea level with some T5s. I know the t5's are holding it back but my Fast 4mill drag port with shearers will eat this 421 by 5-8 bikes.....is there anything I should be looking at as far as why it's a dog up top? It just doesn't seem to pull up top. Haven't done a chop yet but have pulled them after WOT run and they look good Quote Link to comment Share on other sites More sharing options...
mike0chek Posted March 15, 2012 Report Share Posted March 15, 2012 most guys will tell you to do a chop. playing with your mains should give you some results. Quote Link to comment Share on other sites More sharing options...
tedd1 Posted March 15, 2012 Report Share Posted March 15, 2012 Did you do compression and leak down after assembly? Did you do a squish measurement? What kind of head/domes are you using? Where is your ignition timing set? Quote Link to comment Share on other sites More sharing options...
Ieat4strokes Posted March 16, 2012 Author Report Share Posted March 16, 2012 Did you do compression and leak down after assembly? Did you do a squish measurement? What kind of head/domes are you using? Where is your ignition timing set? Compression is around 180 ish each cylinder It's a pro design head, domes were unmarked. But guy my friend bought it from ran race fuel and said they were custom cut. Squish was good and in spec. Have Not done a leak down. Timing is at +6 currently. Jeff built a drag ported 4 mill for me with custom race gas domes and at 190 ish compression told me to run mine at +7 so that's where we started with this one. Found a cracked reed today (which were stock reeds) put in some vf3 and still sputters right before power band. Also ditched his Rickey stator for a stock one and now at least it'll get into power band. But stutters right before power band hits. Have adjusted needle clip and everything. I'm about exhausted lol Quote Link to comment Share on other sites More sharing options...
tedd1 Posted March 16, 2012 Report Share Posted March 16, 2012 Compression is around 180 ish each cylinder It's a pro design head, domes were unmarked. But guy my friend bought it from ran race fuel and said they were custom cut. Squish was good and in spec. Have Not done a leak down. Timing is at +6 currently. Jeff built a drag ported 4 mill for me with custom race gas domes and at 190 ish compression told me to run mine at +7 so that's where we started with this one. Found a cracked reed today (which were stock reeds) put in some vf3 and still sputters right before power band. Also ditched his Rickey stator for a stock one and now at least it'll get into power band. But stutters right before power band hits. Have adjusted needle clip and everything. I'm about exhausted lol OK, sounds like you should be pretty close to me. My next guess would be carb tuning. Time for a plug chop? Quote Link to comment Share on other sites More sharing options...
locogato11283 Posted March 16, 2012 Report Share Posted March 16, 2012 Carbs most likely. Those PJ 34's are very temperamental. Ditch those things and run some 35mm PWK's and be happy. Also, he's giving up at least 5 HP alone with his pipes. Quote Link to comment Share on other sites More sharing options...
mike0chek Posted March 16, 2012 Report Share Posted March 16, 2012 Carbs most likely. Those PJ 34's are very temperamental. Ditch those things and run some 35mm PWK's and be happy. Also, he's giving up at least 5 HP alone with his pipes. very true, i have some 35 pwk's and they are great to tune. Quote Link to comment Share on other sites More sharing options...
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