Tony Lopez Posted June 22, 2009 Report Share Posted June 22, 2009 I need help jetting a 421 Cub with 34 MM PJs on 109 50/50 with Pump 91. When I race I am experiencing hesitation when I shift from 3rd to 4th. The bike just pauses for a second or two and then it takes off. I was racing a Suzuki 450 at El Golfo up the "machorro" for any of you who know this place. Anyway he was a bike ahead of me. About have way I would shift to 4th and the bike whould hesitate or just kind of stayed the same and then it would go all out. By the time I got to the top the guy would be 2 to 3 bike lengths behinde me. My main was a 168. I spoke to the guys at D&M here in Phoenix and they told me that they use a 155 main for this set up. Installed them this weekend but the bike overheated while I was testing it standing still. Seemed to overheat to fast. Was my problem because I was to lean or to rich. It did not feel like a bogg. Should I go up to 172 instead of down? By the way the problem above was in sand with Paddles. Quote Link to comment Share on other sites More sharing options...
TeamRealtreeHD Posted June 22, 2009 Report Share Posted June 22, 2009 (edited) I need help jetting a 421 Cub with 34 MM PJs on 109 50/50 with Pump 91. When I race I am experiencing hesitation when I shift from 3rd to 4th. The bike just pauses for a second or two and then it takes off. I was racing a Suzuki 450 at El Golfo up the "machorro" for any of you who know this place. Anyway he was a bike ahead of me. About have way I would shift to 4th and the bike whould hesitate or just kind of stayed the same and then it would go all out. By the time I got to the top the guy would be 2 to 3 bike lengths behinde me. My main was a 168. I spoke to the guys at D&M here in Phoenix and they told me that they use a 155 main for this set up. Installed them this weekend but the bike overheated while I was testing it standing still. Seemed to overheat to fast. Was my problem because I was to lean or to rich. It did not feel like a bogg. Should I go up to 172 instead of down? By the way the problem above was in sand with Paddles. Your main is way too high. Jump down two sizes and do a plug chop... the bike will feel sluggish and hesitate when rich, which you are. I don't like to take big strides when jetting, as in jumping up/down several sizes. Two on the main at most, then tune from there. You are definately high on the main though. You wiull end up even lower than a 162 when it's all said and done. If you were lean, it would break up, and crack, etc. Edited June 22, 2009 by TeamRealtreeHD Quote Link to comment Share on other sites More sharing options...
Tony Lopez Posted June 22, 2009 Author Report Share Posted June 22, 2009 Your main is way too high. Jump down two sizes and do a plug chop... the bike will feel sluggish and hesitate when rich, which you are. I don't like to take big strides when jetting, as in jumping up/down several sizes. Two on the main at most, then tune from there. You are definately high on the main though. You wiull end up even lower than a 162 when it's all said and done. If you were lean, it would break up, and crack, etc. Well it sounded fine during tuning. It is just that it overheated. The bike was standing still though with no fan. Maybe I am fine at 155. I have a pair of 160. I will take those two just in case I need to change. The problem is that there is no way for me to really test it because it behaves completely different in sand vs payment and there is no real close place where I can test it. Thanks for the input. I was not sure if hestitation was a symtom of being to rich. Quote Link to comment Share on other sites More sharing options...
TeamRealtreeHD Posted June 22, 2009 Report Share Posted June 22, 2009 Well it sounded fine during tuning. It is just that it overheated. The bike was standing still though with no fan. Maybe I am fine at 155. I have a pair of 160. I will take those two just in case I need to change. The problem is that there is no way for me to really test it because it behaves completely different in sand vs payment and there is no real close place where I can test it. Thanks for the input. I was not sure if hestitation was a symtom of being to rich. Your main controls the area of the throttle you were experiencing hesitation at... mine did the same thing, it is very common to see that on cubs. Never let a cub idle to long either because they like to load up and foul plugs, especially if your air screw and pilot are a little fat. 160's will do the trick by the way, atleast get you in the ballpark. Good luck... Put those 160's in it, then find a place you can do a plug chop. That is pinned/sticky up top of this forum I believe. Get the pilot and air screw jetted good out of the hole first before you begin messing with that main by the way. Should be 48-50 on the pilot, 3rd clip on your needle and 1-2 turns on the air screw. Get it to be nice and crisp off idle, then go do a plug chop and call it a day... Quote Link to comment Share on other sites More sharing options...
wesw Posted June 22, 2009 Report Share Posted June 22, 2009 what is your setup port, pipe, etc what is your pilot what is your needle what is your clip position what is your main. how long did you let it idle to overheat have you checked your impeller. Quote Link to comment Share on other sites More sharing options...
Tony Lopez Posted June 22, 2009 Author Report Share Posted June 22, 2009 what is your setup port, pipe, etc what is your pilot what is your needle what is your clip position what is your main. how long did you let it idle to overheat have you checked your impeller. I got it from Vitos. The cylinders are Cheetah cubs and the port is whatever came with it althoug I think they advertise a race port. Pipes - CPI's Needle - DGK Pilot is a 55 Clip - 3rd Main was 168. The Impeller is about 1 year old so it has maybe 10 trips on it. Last time I checked it was when I installed the cub on it and the Crank which was about 6 months or so ago. It was fine. The bike was on for about 2 five minute intevrvals while I was testing it. The intervals were about 30 minutes apart. I was reving it up though. Quote Link to comment Share on other sites More sharing options...
wesw Posted June 22, 2009 Report Share Posted June 22, 2009 your main is way to big try a 158 160 depends on elevation and temps no clue on the water. put a temp gauge on and see what your actually getting. Quote Link to comment Share on other sites More sharing options...
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