670 crankshop twins run fat vs Jaws Twins

[Duct tape Doo]

treed my non X 670 with Jaws twins, found some 2nd hand Crankshop and i have jetted down to some crazy skinny mains and i am seeing less than 1050 F , I still run an airbox and HAC, before i start chasing down HAC issues i thought i would see if any one else noticed that the Cranshop twins run cold. I had contacted Crankshop about the distance to drill the holes for the fast reacting probes so i am confident in the temps, I can tell the sled is fat (not crisp) even on the prairie at - 20 C as i have had the machine for 13 years.
I may buy a HAC at a sled salvage to do some trial and error trouble shooting or keep jetting to unheard of main sizes

 

[flabbajabba]

I was waiting to here about how these worked? I never had EGT's so I got no idea. I could lend you my HAC if you can't find one. I gutted the stock air box and jetted down two from stock on mine. It was all seat of pants for me. I did turn the clickers back two clicks so I thought they worked? I haven't ran that sled since so I don't know what its like now. I never ran that sled at low elevation it was always in Valmount or Mcbride.

Deano670 would probably have run these pipes at some time?

 

[Modman]

What is "crazy skinny mains"? I think stick is about 410, it is concievable that you could go down to 330's. I am at 350's with no HAC and Jaws twins, running towards 1200 F on the EGT and 12:1 on the A/F gauge so I'm still a little fat.

What do your plugs look like?

 

[Duct tape Doo]

The sled is not totally stock, I have taper bored the carbs, rotary is a plate is a 501, Fattened the base gasket and shaved head to .059 squish,gutted the air box, shorty RV boots, i have kept the stock mid needles and seats but i am out of clip settings so i keep out of the mid range, My jaws ran about 1250 F in a long pull with 360 pto,350 mag, i have a set of 330,340's that i can go down to with the crankshop pipes. I always trust my piston wash baseline more than spark plug color and both are confirming that i am fat. This sled is a spare and for my 12 yr old daughter now so i don't need to see 1300 F, I just want her to turn the 156" track and not be the weakest sled in the group

 

[Modman]

The sled is not totally stock, I have taper bored the carbs, rotary is a plate is a 501, Fattened the base gasket and shaved head to .059 squish,gutted the air box, shorty RV boots, i have kept the stock mid needles and seats but i am out of clip settings so i keep out of the mid range, My jaws ran about 1250 F in a long pull with 360 pto,350 mag, i have a set of 330,340's that i can go down to with the crankshop pipes. I always trust my piston wash baseline more than spark plug color and both are confirming that i am fat. This sled is a spare and for my 12 yr old daughter now so i don't need to see 1300 F, I just want her to turn the 156" track and not be the weakest sled in the group

You can trust your plugs too IMO, they change faster than piston wash.

Sounds like you are on the right track, with no HAC and all the mods, you are pulling in much more fuel so jetting down is expected. The taper bored carbs will act like a bigger carb so therefore you need less fuel for the same amount of air. I have 46 mm oval bores and like I said, I'm fat at 350 mains at about 6000 ft, I could go down to 320's probably for anything above that.

You can change the stock needle tubes to AA2's if they are still the AA4's, that will give you some needle e-clip settings back, if you are rich. If you are lean in the mid range then go to AA5s (either 5 or 6, can't remember the next step up), since your daughter might run it there for longer times.

From what I remember, the CS twins did not make as much HP as the Jaws twins (only like 3-5 more HP that stock) so they could be why you are fat.

Hope that helps.