I have a mildly built 360 in a 76 F-150. It had a Holley 650 when I bought and since I am not much of a fan of the Holleys I upgraded to a Speed Demon 750. I cannot seem to get the mix right. I have tried everything there is to try. It will not stay running if it does in fact run at all. Flooding out, running very rich, smoking (white) and all the tell tale signs of too much gas. Help. Please.

 

Smaller jets??? 750 does sound big, I have the Truck Avenger 630?? on my 400, runs great.

 

600 cfm is more around what you need, up to a 650 would be fine to. Edlelbrock sells 600 cfm carbs, and they seem pretty good if you don't want another holley.

You could just use you old holley.

 

Far too big for a mild 360. Especially since BG uses a different standard to flow his carbs. Your 750 speed demon is equivalent to a holley in the 800-850 range, just to give you perspective. Stick with a carb in the 600-650 range. Another thing to remember, is that the Demons have adjustable air bleeds, unlike the standard holleys, and you have to tune them along with the jets.

 

"very rich smoking (white)", that ain't fuel. White is hot combustion with small trace of oil or water in the combustion chambers. Those who hate Holley carbs just haven't spent the time to learn and tune them properly. A 670 SA will feed a 450" motor at 5,400 rpm's, what do you want, a 6,500 rpm 390 with no low end? A 570 SA sounds like the size you need unless you cruise as 4,500. Done venting sorry it's your money.
.....=o&o>.....

 

White smoke is usually water/antifreeze or possibly tranny fluid from a bad modulator valve.
Sounds like the floats may be too high or something is stuck in a needle and seat. The engine should still run even if the carb is a bit too big. Look for gas dripping down into the barrels when it is idling or trying to idle. If it is, then you need to check the float levels and needle and seats.
The fuel level should be at the bottom of the sight glasses in the bowls.

 

Any luck getting the Demon to work? I have been doing a lot of research on the Demon carbs...and the model that you have in the "Speed" Demon is a bit large. You could certainly reduce the jets...and remember...go only two sizes smaller at a time. As mentioned earlier, make sure your fuel level in the floats is near the 1/4" area.

Your ideal carb for your truck would have been either a "Road" Demon 525 or 625. Demon now has the Demon Trucker "Road" carb as well. Those could certainly work in your FE application.

http://www.barrygrant.com/demon/default.aspx?page=5

http://www.barrygrant.com/news/artic...oduct_009.aspx

Tip: To make that Speed Demon 750 work better after changing out the jets...put a 2" 4-hole spacer.

Good luck...and let us know how it went.