IDAHOSHEE Posted August 17, 2010 Report Posted August 17, 2010 Looking for some help, just built a Vito's 421, 20cc domes, 160 lbs compression,shearer in frams, 155 main jets in new 39mm kein pwk's. runs great until it reaches higher rpm's then seems to cut out and sputter, falls flat on it's face. Have tried going both directions with jetting does not change the cutting out. Have tried timing from 0 to 7 deg advanced, does not change the problem. Any advice at this point would sure help. Quote
jbooker82 Posted August 17, 2010 Report Posted August 17, 2010 What stator are you running? OEM or aftermarket? Quote
jbooker82 Posted August 17, 2010 Report Posted August 17, 2010 Your sig says your running a 2:1 or are you running dual 39's. What size mains have you tried? Quote
IDAHOSHEE Posted August 17, 2010 Author Report Posted August 17, 2010 Your sig says your running a 2:1 or are you running dual 39's. What size mains have you tried? Had;nt changed the sig yet, running duel 39's , tried from 152 mains to 188's Quote
jbooker82 Posted August 17, 2010 Report Posted August 17, 2010 I would have guess around a 160 main. You might check the pickup coil gap. Maybe some one who has experiance running those cylinders will chime in. Are they the sleeved stock cylinders, or the sleeper new casting cylinders. Quote
SonOfSand Posted August 17, 2010 Report Posted August 17, 2010 (edited) Looking for some help, just built a Vito's 421, 20cc domes, 160 lbs compression,shearer in frams, 155 main jets in new 39mm kein pwk's. runs great until it reaches higher rpm's then seems to cut out and sputter, falls flat on it's face. Have tried going both directions with jetting does not change the cutting out. Have tried timing from 0 to 7 deg advanced, does not change the problem. Any advice at this point would sure help. Is this you Jason? I had the same problem when I built my 4 mil, it was the pick up coil gap like mentioned above, and make sure the screw on caps on top of your spark plugs are tight, they rattle loose after time. Edited August 17, 2010 by SonOfSand Quote
SonOfSand Posted August 17, 2010 Report Posted August 17, 2010 (edited) Edited August 17, 2010 by SonOfSand Quote
IDAHOSHEE Posted August 17, 2010 Author Report Posted August 17, 2010 Thanks for the imput guys, I will pull the cover tonight and check the air gap. Quote
IDAHOSHEE Posted August 17, 2010 Author Report Posted August 17, 2010 I would have guess around a 160 main. You might check the pickup coil gap. Maybe some one who has experiance running those cylinders will chime in. Are they the sleeved stock cylinders, or the sleeper new casting cylinders. They are the new castings. Thanks for the ideas. I am going to pull the cover tonight to check the air gap. Thought I was on the mark but who knows. Quote
EvilBanshee Posted August 17, 2010 Report Posted August 17, 2010 They are the new castings. Thanks for the ideas. I am going to pull the cover tonight to check the air gap. Thought I was on the mark but who knows. I just finished my 421 from vito's, its been running like shit kinda as well. But i have the stock carbs on it. Tonight im gunna put the 34mill's on it. I think all it needs is some tuning with the jets. time will tell. Quote
SonOfSand Posted August 17, 2010 Report Posted August 17, 2010 I also narrowed the spark plug gap to about .024. Quote
rdzbangshee Posted August 18, 2010 Report Posted August 18, 2010 Looking for some help, just built a Vito's 421, 20cc domes, 160 lbs compression,shearer in frams, 155 main jets in new 39mm kein pwk's. runs great until it reaches higher rpm's then seems to cut out and sputter, falls flat on it's face. Have tried going both directions with jetting does not change the cutting out. Have tried timing from 0 to 7 deg advanced, does not change the problem. Any advice at this point would sure help. my vitos 421 runs best with about + 8 deg on the timing plate, Quote
bigborebanshee Posted August 18, 2010 Report Posted August 18, 2010 I too run the Vitos 421 and had the same problem .It got worse after i went on a trail ride on a dusty day.By the end of the day it would not rev past 3/4 throttle without sputter and coughing.Filter and outerwear were dirty.I dropped the main 1 size and cleaned the filter.It has been running great ever since.I run 34pjs and my mains are at 150. Quote
EvilBanshee Posted August 18, 2010 Report Posted August 18, 2010 I too run the Vitos 421 and had the same problem .It got worse after i went on a trail ride on a dusty day.By the end of the day it would not rev past 3/4 throttle without sputter and coughing.Filter and outerwear were dirty.I dropped the main 1 size and cleaned the filter.It has been running great ever since.I run 34pjs and my mains are at 150. Does she pull pretty hard?? i have a similar set up to yours. Im just waiting for some jets to come in. Quote
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