I have a 1930 Ford Model A pickup with the following setup:  Rebuilt 1973 Chevy 350 V8 bored .030 over  Rebuilt TH350 automatic transmission  Mr. Gasket fuel pump  Edelbrock Performer Intake Manifold with extra 1" spacer  Edelbrock Performer Plus Street/Strip cam  Demon 650 carburetor with K&N filter setup The carb is new and came with the engine when I bought it. I am cannot get the beast to idle down and it runs rich. I just want a cruiser. It has been suggested that I take it off and put on a Rochester Quadra Jet for both economy and power (up to 750 cfm?). What do yall say? Where can I get a good rebuilt one? I will probably have to get a Holly to Rochester adapter to put I on my Edelbrock Performer manifold, right? Any other nightmares that would deter me? Thanks.
That carb a double pumper/mechanical secondary? It is likely that the power valve is staying open or float level is too high. 650 cfm is a good match or your combination. Start with the basics, float level and vacumme rating on the power valve. Then run it wide open and get a plug reading to check the mains. Remember to turn if off before you let off the pedal or it will ruin the reading. If they are OK, commence setting the idle. Idle it down, the adjust screws for max rpm, repeat. Watch out that you don't have too big a cam on the pump.
is that mr gasket fuel pump a high volume pump? maybe its pumping too much fuel into the carb, put a guage on, see what kind of fuel pressure you're getting.
Put a Q-jet on it and don't look back. This carb comes in both 750 and 800 cfm sizes and will run right with any Holley or Demon on a street car as well as some race applications and get better gas mileage too. Gas mileage matters a lot to me, maybe to you too. It won't over carburate smaller engines since the air-valve secondaries will only give the engine as much airflow as it demands, they came on everything from 230-inch Pontiac OHC sixes to Caddy 500 V8s. It's the closest thing to fuel injection as far as carbs go, the engineers at Rochester really did their homework on the metering for those small high-velocity primaries. There's a good reason for the fact that this carb was in used in one form or another for over 20 years. No adapter needed, the Performer intakes are made to accept spread-bore (Q-jet) and square-bore (Holley/Demon).
Put a Quadrajet on it, and be sure the fuel pressure is between 4-4.5 pounds max, and enjoy the great fuel mileage and power. Q-Jets Rule ! Summit Racing has rebuilt Q-Jets in stock, here is a link: http://store.summitracing.com/egnsearch.asp?N=400304+4294925239+4294919007+308353&autoview=sku
listen to draggin'GTO and ahotrod...go with the q-jet. i rebuild carbs as a side business and specialize in those, never had a customer look back after i talked them into putting one on their car. i run one on a 10.7:1 461 olds in a 3800lb car and get 14mpg around town...it's a low 12 second monster don't buy a pre modified one...they are setup too generically to work well on anything. get a good rebuilt one if you don't feel like doing it yourself and then buy the books by cliff ruggles and doug roe on modifying them. do NOT buy a holleyII reman either, those fuckers refuse to acknowledge that there were different rochester divisions and mix and match as they please with poor results.
My neighbor offered me an aluminum intake for Corvette (spreadbore), dual plane, and an old Rochester Quadrajet that will need rebuilt. Are they hard to rebuild? What model of Quadrajet (electric choke) would be the best? Thanks.
you wanna find a 4MV q-jet to have the most options. you can identify those by the two parallel fins going side to side on the lid above the fuel inlet. they aren't hard to rebuild, just a little daunting to some to setup properly. get those books i mentioned and have at it, if you have a basic understanding of simple mechanics you'll be fine. need any other help pm me or i can get you some good links later.
650 sounds like enough, and that intake should help suck whatever that motor needs. I don't think it's under carbed. I would find someone who knows how to tune that carb to help before buying another. I agree, a q-jet will be easier to deal with, but make sure you get some cash out of that demon...
One more important question regarding the Rochester Quadrajet. I see that they had three different types of chokes: heat, divorced, and electric. I am assuming the electric are some of the later ones that do not have the fuel mixture screws on them either. Since I will not be using the stock Camaro intake manifold, how do I hook up the choke on the quadrjet? Thanks.
My 2 cs... The advice to use a q-jet is very good. It will fit your performer manifold and give you great mileage and performance. Buy the books and learn to work on them. You will be very happy . That being said...... the demon should work with your combo as well ! Most likley the problem is fuel pressure. Holley type carbs ( not to piss anybody off, but thats what the demon is ) do not like any more than 6 psi. Check your fuel pressure first, get it set and then work on the tune ( float level,jets, power valve,acc.cam,shooters etc.) Any tuning will not be accurate with too much psi.. 4 psi min, 6 psi max... good luck Dave ;-)
Demon carbs take alot of "fine tuning" I had the same problem with my Demon. took me about 2-3 days to finally get it "right" the 4-corner idle adjustment is a little tricky, and if I remember correctly, I had a bad power valve right out of the box good luck Vance
The Mr. Gasket mechanical fuel pump supposedly puts out 6-8 psi. I suspect the low end at idle and 8+ as she revs up. I have ordered a Mr. Gasket fuel pressure regulator that is adjustable from 1-6 psi. I think I will set it at 4.5 psi to see what happens. The Demon 650 is brand new. As black as the exhaust pipe is and with as much gas as it is using, I suspect you are right and it is just pushing unburned fuel right through the system. A little of that and my gas mileage would plummet. Will keep y'all posted on what happens.
I had the same setup on an OT cutlass supreme except with Holley. Dumped the Holley and put on a qjet. bought the core on ebay, the kit, and rebuilt it myself. Purrs like a kitten now.
What kinda vacuum is the engine pulling at idle? You may need to swap out the powervalve to a lower setting. If turning the idle mixture screws seem to have no affect on idle quality, I bet that's the problem.... If the cam is big, it'll have less vacuum, affecting idle quality and guys raise the idle to get it to smooth out, uncovering the transfer slots, which dumps in more fuel.....that's in addition to the fuel added to the mix from the powervalve, due to low vacuum in the first place. Find out the engine vacuum at idle and the powervalve size. PV should be a lower setting than engine.....it also helps to adjust the SECONDARY throttle blade closing point.....opening it slightly to get more AIR into the engine at idle. Then primary idle can be brought down to a livable level and not idle rich.... The option I personally would do though is throw the BG carb in the GARBAGE and get a Holley/Carter/Q-Jet, etc......
The 650 is fine in regards to the application . Few questions for you.... how much timing does the motor have at idle? where is the float level set at? how far out are the mixture screws? how much transfer slot is showing on both sides on the bottom of the carburetor? vacuum or mechanical secondary and are you using an hei distributor? if so where is the vacuum line hooked up at?
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