SpeedRacer88 Posted August 7, 2011 Report Share Posted August 7, 2011 i got a HJR 421 Cub. Im a aircraft mechanic so im mechanically inclined. i got out the military and moved back home. i moved from 3,000 feet to sea level and of course i blew the top end. i'm getting it back together and i went ahead and bumped the compression up to 165psi for AVGAS. i ride mostly wide open trails maybe about twice out of my ride i might have to slow down through a tight spot. so with that said what can i bump my timing to? what should i start with in jetting. and do i need 100percent AVGAS or not? my mods in my sig ps what else can i do to this thing? i ride with two honda 450 dirtbikes and a modded rm250 and they are still kicking my ass Quote Link to comment Share on other sites More sharing options...
locogato11283 Posted August 7, 2011 Report Share Posted August 7, 2011 I'd run that on +4 timing. Yes, you will need to run the 100 octane for the increased compression and timing. Your jetting should be right around 160-162 main and 45-48 pilot. Are the bikes beating you straight line or in the trails? If straight line, you need to check traction. If it's in the trails, you're probably just screwed. Quote Link to comment Share on other sites More sharing options...
SpeedRacer88 Posted August 7, 2011 Author Report Share Posted August 7, 2011 I'd run that on +4 timing. Yes, you will need to run the 100 octane for the increased compression and timing. Your jetting should be right around 160-162 main and 45-48 pilot. Are the bikes beating you straight line or in the trails? If straight line, you need to check traction. If it's in the trails, you're probably just screwed. straight line, im running 16/40 gearing Quote Link to comment Share on other sites More sharing options...
TNTS355 Posted August 7, 2011 Report Share Posted August 7, 2011 straight line, im running 16/40 gearing I run +7 on my cub. I would go with stock gearing are they beating you out of the hole? Quote Link to comment Share on other sites More sharing options...
SpeedRacer88 Posted August 7, 2011 Author Report Share Posted August 7, 2011 I'd run that on +4 timing. Yes, you will need to run the 100 octane for the increased compression and timing. Your jetting should be right around 160-162 main and 45-48 pilot. Are the bikes beating you straight line or in the trails? If straight line, you need to check traction. If it's in the trails, you're probably just screwed. and my bike was dialed in professionally at 165 main CEG needle middle clip 52 pilot 1 1/2 turn out on the air screw when i was in south dakota Quote Link to comment Share on other sites More sharing options...
SpeedRacer88 Posted August 7, 2011 Author Report Share Posted August 7, 2011 I run +7 on my cub. I would go with stock gearing are they beating you out of the hole? i never really lined up and raced them because i usually lead and when we come up on a str8 they all just fly by... im not a beginner by any means i've been riding since i was 8 they all been riding no more than 5 years im tired of the shit talking.. and +7 wouldn't hurt anything? Quote Link to comment Share on other sites More sharing options...
beebs Posted August 7, 2011 Report Share Posted August 7, 2011 They were beating you when you were not setup correctly before it blew up? Shouldn't have a problem after the guys on here help you setup correctly. Quote Link to comment Share on other sites More sharing options...
SpeedRacer88 Posted August 7, 2011 Author Report Share Posted August 7, 2011 They were beating you when you were not setup correctly before it blew up? Shouldn't have a problem after the guys on here help you setup correctly. your probably right but they beat my by so much its kind of hard to believe i will be any more competitive i mean they would str8 up pass me and walk away nothing gradual especially the rm250 Quote Link to comment Share on other sites More sharing options...
beebs Posted August 7, 2011 Report Share Posted August 7, 2011 HJR built and setup my 4-mill stock cylinder motor, and the honda 450 bike that I ride with looses on the straights in the gravel and pavement. Quote Link to comment Share on other sites More sharing options...
SpeedRacer88 Posted August 7, 2011 Author Report Share Posted August 7, 2011 HJR built and setup my 4-mill stock cylinder motor, and the honda 450 bike that I ride with looses on the straights in the gravel and pavement. 450 dirtbike or quad? Quote Link to comment Share on other sites More sharing options...
beebs Posted August 7, 2011 Report Share Posted August 7, 2011 Dirt bike. He also has it geared a little higher. Quote Link to comment Share on other sites More sharing options...
SpeedRacer88 Posted August 7, 2011 Author Report Share Posted August 7, 2011 anyone have any info regarding the timing and jetting? Quote Link to comment Share on other sites More sharing options...
beebs Posted August 7, 2011 Report Share Posted August 7, 2011 Your jetting seems really close to start out with. I would think you would end up close to what loco said, and also as said start with +4 timing. You sure the topend went because of jetting? Quote Link to comment Share on other sites More sharing options...
TNTS355 Posted August 8, 2011 Report Share Posted August 8, 2011 Your jetting seems really close to start out with. I would think you would end up close to what loco said, and also as said start with +4 timing. You sure the topend went because of jetting? I agree with the +4 to start, then work your way up. Mine was put on the dyno and ran best at +7 and we went all the way to +11. Did you open the motor up or did someone else? I am just wondering what was going on in there to blow it. Quote Link to comment Share on other sites More sharing options...
lms1977 Posted August 8, 2011 Report Share Posted August 8, 2011 Hard to believe that a rm250 is kicking your ass is it all worked up? Quote Link to comment Share on other sites More sharing options...
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