jeffs

This is a question for guys with demon carburators in Colorado.

What primary and secondary jets, and power valve are you guys puting in your demons at this altitude? My stock 750 speed demon has 76 pri; 83 sec; a 6.5 power valve (I'm running 13 in. of manifold vacuum). Also, did you go with a lighter spring in your vacuum secondaries. Look at my sig and give me any suggestion on setup. I want to get it as close as possible before I drive up to see Lars.

If Lars reads this, what do you think?

Jeffs

Paul 75 L82

jeffs, I'm in South Florida, about sea level. I can't help you with the jets, but I went with one step larger power valve and a lighter spring and it made alot of difference. Also I set my idle jets with a vaccum gauge and that worked well also. Good Luck.

gkull

74 and 81 demon 750 mech seconds at ruffly your elevation

clem zahrobsky

reduce the AREA of the jet 2% for every 1500 ft. you are above sea level. if you are at 6000 ft gkull is correct


[Modified by clem zahrobsky, 5:55 PM 12/18/2001]


[Modified by clem zahrobsky, 6:04 PM 12/18/2001]

jeffs

Thanks guys. Any suggestions on the power valve, my tag show it a 6.5. Also, the tag shows a #31 SQ. That might be the squirter, not sure.

clem zahrobsky

if you have a flat spot at part throttle you may want to try a 8.5 PV.

lars

Jeffs -
We have tried several different jet changes in the Demons we've been installing. It appears the Demons, unlike Holleys, are jetted pretty lean and crisp out of the box. On any other carb, Clem's formula is completely correct. But on these Demons, we've been dropping the jet size only 1 size for best performance at 6,000'. We've arrived at this after lots of 0-60 runs with a Vericom Performance Computer. Dropping the jet size 2 or more sizes results in a steep drop-off in performance - very noticable - you end up with a sag in the acceleration, and exhaust gas temps go up significantly (we've been shooting EGT's with IR thermos).

If you'd like to stop up and play with the setup a little, that sounds like fun. I'm off work from 12-22 through the first of the year. I'm sure we'll have some nice days in there, so give me a call and stop on up for a little tuning and tweaking. Do you have a good fuel line without rubber hose? If not, we can build you a fuel line, too - lemme' know. (303) 604-6376 (h)

gkull

Lars - I'm using 74 & 81 6.5 on a tall single p manifold. At cruise I have 16+ inches of vacuum. I'm just wondering if my Demon's boosters might be of a differrent model allowing for leaner jetting? Demon carbs have a whole array of booster types and as you know certian designs create a higher pressure drop. So a given jet size will flow more. My other variable is I use Maxjets which are true 1/1000th's sizes and I go to a chart which gives the equivolent Holley jet #

Jeff's .031 is the squirter hole dia. Mine are drilled out to .046 I messed with all kinds of power valves and came back to 6.5 My old 750 demon was the chokless four squirter version. I since put on a 825 race demon with 77/85's