Yet another SBC jetting question
 

Trying to figure my carb out. It's a 650 demon on a vortec 350. I know I need to do plug checks but I'd like to get close before having to raise the hatch and stand on my head after every run to get plugs out. Also i am not crazy about shutting the enine off at 60+ mph Carb came stock with 72 primary and 80 secondary jets. I'm currently running 70's and 78's. Wot rpm is around 5200-5400. I'd like to get this thing close without melting it down from a lean condition. Where would you guys start? Oh yeah, elevation is 3000 above sea level. If you need more info just ask. I promise to buy beers for all that offer advice:evilb:

il take some of those beers,keep in mind,a car going 35-40 mph is not working hard to maintain that speed,your boat at that speed is working pretty hard,and you are well into the throttle,i would go slightly ritcher than the way it came from holley,you are only loosing a small amount of power,not even enough to loose 1 mph,it is just not worth leaning it to death,espically since you will see no gain.

Dyno!!

Thanks Mike. Im going to buy a stainless marine exhaust setup over the winter with some o2 bungs so I can run an A/F ratio gauge and tune it correctly. Just trying to get close for now and not spend a ton of time screwing around with it. Just want to enjoy it safely for this year

That would be nice but there isn't one anywhere near me, plus I've had the motor out as many times as I care to for now to fix other issues. Just gonna hold out for the exhaust upgrade and A/F gauge.

i recomend the fast dual senser unit,got mine online from a dist in tenesee,nice unit with 12 foot cables.

That's the one I've been looking at. Glad to hear some positive results with it.

So if the factory jets where 72/80 should I go with a 73/81 or 74/82 just to be safe? Demon told me they are calibrated for sea level and I could actually drop 4 jet sizes and be ok but I thought that sounded like a little much and only went down 2.

Once you start using a wide-band you will never go back. It is super easy and invaluable. I would not 'tune' another motor without one, EFI or carb.