Carb tech, i need tuning help.

[ExplodingGopher]

Lately i tried adjusting my Demon 850 DP carb and it is running really really rich right now, like burn your eyes and nose at idle kind of rich. The butterflies are set to be open equal amounts, mixture screws are out i think 2+ turns. If i try to lean it out at idle, it idles fine but once the secondaries open, it stumbles/pops through the carb. If i keep it rich, it runs ok but its just killing my already minimal gas mileage. Carb has stock jets in it which i think are 84 in the front and 93 in the back, seems a little big. Any ideas?

 

[iskwezm]

you might wanna post this in the classic area,get more hits

have you checked the power valve?

 

[Thenemesis]

jets are killing ya.. i would first try out a different size.. thats what happened to me and my holley i had.. runnin 84's on a 650 lol lil to big

 

[rd]

This is a lot of carb, and I have no direct experience, the closest was a Holley 750 dp.

Not sure, but I would check things like making sure that the butterflys are closed enough that the idle discharge passages are uncovered, but the idle transfer slots are not open until after you press the throttle. It sounds like it is trying to idle with the idle discharge and the transfer discharges. Float levels may be higher than needed.

I have had this with some Holleys, when the secondary gaskets get old and leak.

 

[srothfuss]

Smaller Primary jets will let you riched the A/F meter and reduce your popping & backfiring.