Carburetor Question (To Jet or to Go Up In CFM) - Page 2 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

cadillac_al · 08-17-2016, 07:37 PM

I think that cam is made to idle rough. I'd say it will be trial and error with the timing to get it to run as good as it ever will. I'm sure the low compression 1986 engine isn't helping. You may get it to sound bad ass though. Keep tinkering.

Marv D · 08-17-2016, 09:01 PM

Agree. The "thumper' cam will never idle right
BUT, a 243°@ 0.050" is far from HUGE in a 454. The Edelbrock RPM small blockcam is only 7° less than that, intended for a 350" motor, and will idle at 750-800RPM all day long. Another 100 cubic inches would gobble up 15+° and never know its there.

The fact that you have issues with TWO carbs,, you should listen to the fella's here and check elsewhere. Timing,, absolutely if you don't KNOW where the timing is you need to find out/
My first suspect in a backfireing, poorly running motor is the cam has lost an exhaust lobe or 3.

Get the timing set properly and if you still have issues, that neither carb will cure,, time to cut a oil filter open to see how much iron debris is in it,, , and then pull a rocker cover and see how many lobes are wiped.

cableguy0 · 08-17-2016, 10:10 PM

Quote:

Originally Posted by KyleSeal

http://www.jegs.com/i/COMP-Cams/249/CL11-602-4/10002/-1
There's the cam. Also an Eddy Performer RPM intake.
Posted via Mobile Device

Well you just found a good portion of your problem. That POS noisemaker isn't good for anything but making noise. That cam isn't big though by any stretch for a 454. YOU NEED TO CHECK YOUR TIMING. If you don't know what is then it isn't right. Setting timing by ear or anything like that is NONSENSE. Put a timing light on that engine. We cant help you if you don't do the basic troubleshooting stuff and give us some info.

**KyleSeal** · 08-18-2016, 01:27 PM

As I am repeatedly saying: I cannot get it to run long enough or at constant enough RPM to get a timing reading. I put a 5 psi fuel regulator on it and it fires up easier now. I'm going to try turning the distributor a little each time firing up until I find a spot that is okay.

cableguy0 · 08-18-2016, 08:10 PM

Put the engine at 3k rpm and see where the timing is. You will need an advance timing light but you need one anyway if you want to set the total timing properly.

**KyleSeal** · 08-20-2016, 09:49 AM

Put a new 750 double pumper, a 4776 not a 4779-9 750, but a regular street 750. Fired up. We're just adjusting it down now.
Posted via Mobile Device

**KyleSeal** · 09-13-2016, 02:38 PM

Tuned that 750 DP I purchased, drilled the butterflies and threw a tiny powervalve in it, corrected the MSD box wiring, put a new distributor and spark plugs in it and its driving around again. Another issue I had was a bad alternator. New one fixed it.

**Captainfab** · 09-13-2016, 11:10 PM

A 4776 is a 600 cfm double pumper, not a 750.

Quote:

Originally Posted by KyleSeal

Put a new 750 double pumper, a 4776 not a 4779-9 750, but a regular street 750. Fired up. We're just adjusting it down now.
Posted via Mobile Device

Did you ever determine what your timing is?

Quote:

Originally Posted by KyleSeal

Tuned that 750 DP I purchased, drilled the butterflies and threw a tiny powervalve in it, corrected the MSD box wiring, put a new distributor and spark plugs in it and its driving around again. Another issue I had was a bad alternator. New one fixed it.

08-17-2016, 07:37 PM	#26
cadillac_al Registered User Join Date: Oct 2013 Location: Maine Posts: 2,376	Re: Carburetor Question (To Jet or to Go Up In CFM) I think that cam is made to idle rough. I'd say it will be trial and error with the timing to get it to run as good as it ever will. I'm sure the low compression 1986 engine isn't helping. You may get it to sound bad ass though. Keep tinkering. __________________ 76 Chevy K20 76 GMC K15 77 Chevy C10 77 Chevy K10

08-17-2016, 09:01 PM	#27
Marv D Registered Truck Offender Join Date: May 2008 Location: hells training ground (aka Ariz) Posts: 3,118	Re: Carburetor Question (To Jet or to Go Up In CFM) Agree. The "thumper' cam will never idle right BUT, a 243°@ 0.050" is far from HUGE in a 454. The Edelbrock RPM small blockcam is only 7° less than that, intended for a 350" motor, and will idle at 750-800RPM all day long. Another 100 cubic inches would gobble up 15+° and never know its there. The fact that you have issues with TWO carbs,, you should listen to the fella's here and check elsewhere. Timing,, absolutely if you don't KNOW where the timing is you need to find out/ My first suspect in a backfireing, poorly running motor is the cam has lost an exhaust lobe or 3. Get the timing set properly and if you still have issues, that neither carb will cure,, time to cut a oil filter open to see how much iron debris is in it,, , and then pull a rocker cover and see how many lobes are wiped. __________________ Still playin with trucks, even at my age! When you're dead, it's only a problem for the people around you, because you don't know you're dead. .....It's kinda the same when your STUPID. I just did my taxes and reviewed my SS statement. Thanks to the current administration it looks like I will only have to work till noon on the day of my funeral.

08-18-2016, 01:27 PM	#29
KyleSeal Senior Member Join Date: Mar 2014 Location: Toano, VA Posts: 893	Re: Carburetor Question (To Jet or to Go Up In CFM) As I am repeatedly saying: I cannot get it to run long enough or at constant enough RPM to get a timing reading. I put a 5 psi fuel regulator on it and it fires up easier now. I'm going to try turning the distributor a little each time firing up until I find a spot that is okay. __________________ "Sometimes I do serve as a good bad example. Glad to be of service." My Build Thread (1967 C10, lowered, EFI, daily truck): http://67-72chevytrucks.com/vboard/s...d.php?t=830809

08-18-2016, 08:10 PM	#30
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,948	Re: Carburetor Question (To Jet or to Go Up In CFM) Put the engine at 3k rpm and see where the timing is. You will need an advance timing light but you need one anyway if you want to set the total timing properly. __________________ Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member.

08-20-2016, 09:49 AM	#31
KyleSeal Senior Member Join Date: Mar 2014 Location: Toano, VA Posts: 893	Re: Carburetor Question (To Jet or to Go Up In CFM) Put a new 750 double pumper, a 4776 not a 4779-9 750, but a regular street 750. Fired up. We're just adjusting it down now. Posted via Mobile Device __________________ "Sometimes I do serve as a good bad example. Glad to be of service." My Build Thread (1967 C10, lowered, EFI, daily truck): http://67-72chevytrucks.com/vboard/s...d.php?t=830809

09-13-2016, 02:38 PM	#32
KyleSeal Senior Member Join Date: Mar 2014 Location: Toano, VA Posts: 893	Re: Carburetor Question (To Jet or to Go Up In CFM) Tuned that 750 DP I purchased, drilled the butterflies and threw a tiny powervalve in it, corrected the MSD box wiring, put a new distributor and spark plugs in it and its driving around again. Another issue I had was a bad alternator. New one fixed it. __________________ "Sometimes I do serve as a good bad example. Glad to be of service." My Build Thread (1967 C10, lowered, EFI, daily truck): http://67-72chevytrucks.com/vboard/s...d.php?t=830809

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