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34pj’s 70mm jetting


Biggt613

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Ok i have read alot of jetting threads and am familiar with dialing carbs in half decent. However i am about too put a new top end in with new carbs and it will be -20 when i start plug chops. So right now stock carbs,stock stroke, basically stock jugs, pc platnums, +4 timing, vf4’s, 50/50 c12/premium, no airbox lid, kn filter. -7Celcius 300main(-20 would be 320) 30pilot and its pretty crisp and tan. New set up will be sleeved 70mm cylinders. Stage 2 porting stock stroke, vf4’s, pc pipes, +4, kn filter. Stage 4 coolhead, 19cc domes, 34mm pj’s, 50/50 fuel 15/40 gearing. Lowered and widened for ice racing in canada. Now can someone give me a baseline/guideline to start with. Im a thinking 175/55 to start. Fwiw i also have leak down tester(thanks south texas) and carb sync on hand. I know its probably posted somewhere but not much out there for 70mm stock strokes. I got them cheap so sent them back to harry mcdermott to clean up and match pistons. 
thanks guys

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I used to run a very similar combo on the ice. Turn the choke knobs in all the way and mark the knobs. Turn them back out 7 1/2 turns. Run the air screws in all the way and back them out 1/2-3/4 of a turn. 58-60 pilots, 160-165 mains. That set up won’t move as much air and fuel as other modern set ups with similar displacement as the big bore sleeves tend to choke out the transfer areas a little bit. What needles do you have in the carbs? CGL or CEL?

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20’s F.  Start with the CGL’s second from the bottom clip. This will all probably be a little fat, but if it will still pull clean leave it be. If it’s a little blubbery, put the needle at middle clip, and back the main down one size at a time. Once the sun goes down on the ice, it’ll want more fuel. There were days where you start riding in the sun and make two jet changes as it gets colder when the day goes on and clouds come in or sun goes down.  I’ve played with power jets and the Dial a jet on my old PJ’s and actually liked the dial a jet quite a bit. It lets you keep making the needed changes with out needing to pull the carbs to do mains. 

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Thanks alot. I am expecting to be in the 0-10f range most of the time but its about 32f now. Was pulling motor apart last night and organizing the big bore stuff. My 1 piece boss billet intake with the v4’s will push my carbs back 3/4” or so. I dont think my airbox will fit so i am ordering uni pods tomorrow. Would have had everything together but when shop took new piston out of box to match with jugs they for got to put rings back in. With the pods i will probably start at 175 mains and work down. 

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  • 2 weeks later...
On 1/5/2020 at 8:16 AM, Biggt613 said:

Thanks alot. I am expecting to be in the 0-10f range most of the time but its about 32f now. Was pulling motor apart last night and organizing the big bore stuff. My 1 piece boss billet intake with the v4’s will push my carbs back 3/4” or so. I dont think my airbox will fit so i am ordering uni pods tomorrow. Would have had everything together but when shop took new piston out of box to match with jugs they for got to put rings back in. With the pods i will probably start at 175 mains and work down. 

Update?

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just had her out for a rip. Had the petcock seals leaking kept flooding out. Started with 170mains 58 pilot cgl 4th clip. Idle 7 turns out. Its was close but had a lag coming onto needle and fell off on the main. Now i am at 172 main 5th clip. 58 pilot idle 8 turns out. Its -25 out here and it flat out rips!! Syncd carbs. Idles dead even. I turned my neighbourhood into a flattrack lol. Its crisp need to plug chop the main yet but it feels good. Oh and i am sitting at 195 psi on bith cylinders and running straight c12 32/1 with dominator. I cant even explain how jacked i am to get this beast in the ice. Thanks alot man

29FDFFE9-7078-4233-ABCD-AF2C4BFEA8F7.jpeg

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10 hours ago, Biggt613 said:

just had her out for a rip. Had the petcock seals leaking kept flooding out. Started with 170mains 58 pilot cgl 4th clip. Idle 7 turns out. Its was close but had a lag coming onto needle and fell off on the main. Now i am at 172 main 5th clip. 58 pilot idle 8 turns out. Its -25 out here and it flat out rips!! Syncd carbs. Idles dead even. I turned my neighbourhood into a flattrack lol. Its crisp need to plug chop the main yet but it feels good. Oh and i am sitting at 195 psi on bith cylinders and running straight c12 32/1 with dominator. I cant even explain how jacked i am to get this beast in the ice. Thanks alot man

29FDFFE9-7078-4233-ABCD-AF2C4BFEA8F7.jpeg

Air screw 2 turns out

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