Which carb for my 340? Also, bad Holley fuel pump?

[dano]

Now that I will be putting my 340 back into my Dart, I'm reviewing some issues I had with tuning the motor. It wants to run rich, plugs are pretty black and sooty. I have both a new Road Demon 625 and a new Holley 3310 750 Vacuum secondary carb. Both wanted to run rich, doing some looking I have a Holley 12-360-11 fuel pump http://www.summitracing.com/parts/HLY-12-360-11/ and have read there was some issues with the Holley pumps putting out way more pressure than needed, even regulated (I currently have no regulator or FP gauge) So I plan to use a stock pump and install a gauge and regulate if necessary. Which of the two carbs would work best for my application? According to Demon, the 625 is too small for my cam, and Holley states a 600 or 750......? Here's the rundown.

340 (~350cid due to .060 over)
~10.5:1 compression (Forged stock repalcement)
Weiand Steath Intake, gasket matched ported
Lunati VooDoo 60403
-Advertised Duration (Int/Exh): 268/276
-Duration @ .050 (Int/Exh): 226/234
-Gross Valve Lift (Int/Exh): .494/.513
-LSA/ICL: 110/106
-RPM Range: 1800-6200
Ported J heads 2.02/1.6
Comp Adj Rockers
Dougs Headers, 2.5 exhaust
4 speed (not an O.D.)
3.91:1 gears

Car is a driver, no racing, I've but too much money it it to wreck it!

Also any in site on the Holley fuel pump would be helpful.

Thanks!

 

[1wild&crazyguy]

750 holley, try lowering the float levels some to counter the presumed high fuel psi, if thats the case.
Lower float with car running to see if thats it, you want the fuel to be right at the bottom of the sight holes.

also time it to 18* initial and then set the blades/idle speed, then mixture.
I would set the idle screws 3/4 turn out to start, once the throttle blades/initial timing is set.
This is a way to easily find out if you are/were running idle off the main circuit instead of the idle circuit.

report when done.

 

[70aarcuda]

you might want to check your engine vacum and compare it to your power valve in your holley...

also you might need to open up the secondaries throttle blade a hair to let more air in while it idles...

 

[1wild&crazyguy]

you might want to check your engine vacum and compare it to your power valve in your holley...

also you might need to open up the secondaries throttle blade a hair to let more air in while it idles...

right on!

I spaced on that, PV could be open at idle, though while cruising the vacuum will be plenty to keep it closed.

 

[dano]

750 holley, try lowering the float levels some to counter the presumed high fuel psi, if thats the case.
Lower float with car running to see if thats it, you want the fuel to be right at the bottom of the sight holes.

also time it to 18* initial and then set the blades/idle speed, then mixture.
I would set the idle screws 3/4 turn out to start, once the throttle blades/initial timing is set.
This is a way to easily find out if you are/were running idle off the main circuit instead of the idle circuit.

report when done.

On setting to 18*, my timing cover is the 70 and up style that is cast in and only goes to 10*, how do i go about finding 18*?

 

[dgc333]

If you are using the car strickly on the street you will be much happier with the 625.

I have a 360 built much the way your 340 is and I have had 600, 670, 725 & 750's on. The driveability is much better with the smaller carbs and there is barely a noticable difference on the top end with the 600 and no noticeable difference with the 670.

The Demon is rated differently than the 670 Holley I am currently using, using the same method they are equivalent.

 

[DOUGIE800]

Im certainlly no expert dano, Looking at your goods your quite close to be with your engine. I have 3.73's little smaller cam and only .040 over with 10 1/2 slugs. But I went with a 750 DP from Bigs performance. Now lots people told me different things but listened to the guy that built my engine he said you can easily go with the 750 with my set up. Havent ran It down the track with the bigger carb(went from a 650 DEMON) but like it better all around. When I ran down the quarter with smaller carb and 3.55's ran 14.3@102 . Bigs Carbs are expensive but at this point In time I would say worth It. My 2 cents Dhttp://www.cardomain.com/ride/2482122

 

[1wild&crazyguy]

On setting to 18*, my timing cover is the 70 and up style that is cast in and only goes to 10*, how do i go about finding 18*?

look at the distance between 0 & 10, then guesstimate or set it [the line on the balancer] at about the same spacing.

OR get a dial back timing light and just set the dial to 18* and zero the mark on the balancer with the 0 on the cover.

 

[2 Darts]

For a street car, I vote for the 625 cfm. You'll probably get better ¼ mile results with the larger carb, but for the street, the 625 will give better throttle response and economy.

Black soot on plugs? Check ignition, idle mix, and choke operation first. After that, re-jet the Demon. Sadly, there is no formula for a silver bullet combination of primary/secondary jets for any engine. The SWAG would put your combination between a 80 primary, 84 secondary to a 60 primary, 64 secondary. If you must err, err on the rich side. Good luck.