Carb Problems...... - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Restrorob · 10-19-2008, 11:15 AM

Hello all speed freaks,

I posted this in the engine section;

Quote:

Originally Posted by Restrorob

Hey All,

I bought a 97 GMC (sig line) with a 502 Crate and Demon carb that I can't find ANY ID numbers on.

Problem is it randomly starts flooding by the float needle valves, The primary one time the secondary the next. I have dropped the tank and it's clean as a baby's bottom, I have cleaned the carb and replaced both float needle valves setting the fuel level half way in the sight glasses.

It has a in-line fuel filter right after the frame mounted Holley red fuel pump and another just before the non-returning fuel pressure regulator. The regulator is set just a little above 6 lbs. which I believe I read 6/7.5 lbs. was OK.

Any ideas why this dang thing is doing this ?

It's getting un-reliable to drive to cruise-in's......

Thanks for any help !

Rob

My new question is;

Since this is a pos Demon with Holley float valves and no id numbers how would I determine which Edelbrock carb would run this 502 ? The only info I have is it's a 97 (installed when truck was new) with iron heads in which I believe would be the 450 hp version.

Could someone shed some light on my situation ?

Thanks

Mykk · 10-19-2008, 01:03 PM

streetable carb cfm = rpm x displacement / 3456 x 0.85

6000 x 502 / 3456 x 0.85 = 740.8cfm

racing carb cfm = rpm x displacement / 3456 x 1.1

6000 x 502 / 3456 x 1.1 = 958.7cfm

I'd say a 750 - 800cfm will do just fine for a driver, that "racing carb" figure sounds extreme.... granted I had two edelbrock 500cfm four barrels on a cammed 454.

Restrorob · 10-19-2008, 01:21 PM

This truck is no racer but just a show cruiser so I would think the 750/800 would do me just fine.

Thanks for the help Mykk.....

djracer · 10-19-2008, 09:39 PM

buy a fuel injection setup for it!

RatPwrd72 · 10-20-2008, 11:34 PM

Ditch the Demon. Buy a used Holley 3310 750 vac secondary carb. Order a Proform main body and secondary block so you can jet the back. Install said parts with fresh rebuild (I like the Barry Grant kits). Drive the wheels off of it....

10-19-2008, 01:03 PM	#2
Mykk Registered User Join Date: Apr 2005 Location: Prescott Az Posts: 55	Re: Carb Problems...... streetable carb cfm = rpm x displacement / 3456 x 0.85 6000 x 502 / 3456 x 0.85 = 740.8cfm racing carb cfm = rpm x displacement / 3456 x 1.1 6000 x 502 / 3456 x 1.1 = 958.7cfm I'd say a 750 - 800cfm will do just fine for a driver, that "racing carb" figure sounds extreme.... granted I had two edelbrock 500cfm four barrels on a cammed 454. Last edited by Mykk; 10-19-2008 at 01:07 PM.

10-19-2008, 01:21 PM	#3
Restrorob The One And Only !!! Join Date: Jan 2007 Location: Hole in the woods Florida Posts: 4,567	Re: Carb Problems...... This truck is no racer but just a show cruiser so I would think the 750/800 would do me just fine. Thanks for the help Mykk..... __________________ 93 Jeep XJ 88 Buick La Sabra Toys; 88 TA-GTA in the works.... 97 GMC Ext. Cab 502 Crate 5 Spd......Sucks Gas But Haulz Azz ! The primary function of an Engineer is to make it difficult for the Fabricator and impossible for the Mechanic. *"Why go out preserved when you can go out beat up, worn out, sliding in sideways screaming, Holy Sh!t What A Ride" !!!*

10-19-2008, 09:39 PM	#4
djracer Registered User Join Date: Feb 2001 Location: Wetumpka, Al, U.S. Posts: 8,891	Re: Carb Problems...... buy a fuel injection setup for it! __________________ Kevin Special Thanks to All who have helped on the TRUCK! My Pass Time Show http://s129.photobucket.com/albums/p...Chapter1-0.mp4 So Far my best Times are: Motor only: 6.44 1/8 @ 104.13 10.39 1/4 @ 125.83 Nitrous Times: 5.785 1/8 @ 118.65 with a 1.336 60ft 9.168 1/4 @ 142.58 with a 250 shot dead out of the hole!

10-20-2008, 11:34 PM	#5
RatPwrd72 Registered User Join Date: Jan 2005 Location: Maysville, OK Posts: 227	Re: Carb Problems...... Ditch the Demon. Buy a used Holley 3310 750 vac secondary carb. Order a Proform main body and secondary block so you can jet the back. Install said parts with fresh rebuild (I like the Barry Grant kits). Drive the wheels off of it.... __________________ 1972 Chevy Cheyenne Super- Pump gas 496,TH-400, TCI Stall, 3.73's,Ochre & White two-tone w/Olive Interior 1967 Chevy Short Step Drag Truck-Iron Headed 468 Making Memories My momma took me off the bottle years ago.....



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