Jetting a speed demon

[Musclecar]

I have a zz502 and it came with a holley 850 vacuum secondary carb. I yanked it off and installed a speed demon 850 mechanical secondary carb. Right now it is jetted 80 primary/88 secondary. I think the primaries may be ok but when I open the secondaries I think it is getting too much fuel. Any ideas what jetting might work best for this application? Street driven..no racing... well,not on the track anyway :D Thanks

[Blown353]

My experience has been that Demons are way too rich out of the box, typically by about 6-8 jet sizes the primary side and even fatter on the secondary side; usually I end up having the secondary jets about 4-6 sizes bigger than the primaries.I've messed with over a dozen Demons, both Road Demons, Speed Demons, King Demons, and a couple of their 6-shooter setups and they were all pig-rich as delivered.

It's hard to say without driving your car and checking the plugs but my guess is you'll end up somewhere around 76/82 for jetting, probably even a little leaner.

Also, if it's a brand new Demon completely gut it and clean it-- you might be surprised how many burrs and debris comes out of the main body/airbleed passages/metering blocks... it can cause all sorts of driveability issues depending on where the "junk" goes and what it clogs.

[Musclecar]

Thanks for your reply.. The carb is used. It came off a buddy of mines 496 which is putting out about 650hp so I'm sure it will need to be jetted down. I may try going 78/84 and see how it works out. Right now it is at 80/86 and it is rich so I may swap them out tomorrow and see how it works out.. Thanks again :D

[Blown353]

Thanks for your reply.. The carb is used. It came off a buddy of mines 496 which is putting out about 650hp so I'm sure it will need to be jetted down. I may try going 78/84 and see how it works out. Right now it is at 80/86 and it is rich so I may swap them out tomorrow and see how it works out.. Thanks again :D

Cool. Just keep an eye on the plugs and wideband (if you have one.)

Don't forget your powervalve/shooter/etc requirements may be different too.