G'day, this is my first post so hopefully I do it right. I have a 73 C20 454which is running richer in cyl 2,6,3,7 than cyl 1,5,4,8. plugs in cyl 1-8 are a very light brown/tan while cyl 2-7 are very dark. Is this normal for a 454 (only other bbc I've had was a 402 in a project)?

I've read that the there is a difference in the two sets of combustion chambers which is why the trumpets on Hillborn Style injection are set to staggered lengths-could the manifold not be designed with this in mind and therefore give me my problem?

The truck runs great. I'm mainly curious as to why and if there is a relatively easy fix.

Edelbrock Performer manifold
Edelbrock AVS 800 with 3/4" open adapter
Cam sounds stock
HEI
Stock exhaust manifolds


Thank you, Steve

 

Hi Rusty454,

Welcome to the Chevy Forums.

Assuming, of course, that your firing order is 1-8-4-3-6-5-7-2, I can't help but notice that the fuel rich cylinders are almost all in the second half of the firing order.

I'd start with basics, verify the firing order, make sure the HEI coil, rotor ,cap, and ECM are all up to snuff, as well as the vacuum advance.

If the system ever sat for awhile, gas could have evaporated along the fuel system. The jets and pathways could simply be partly blocked creating uneven combustion for some cylinders.

 

Thanks I'll have a look at that. Carby is fairly new but I'll give it a clean. Dizzy is new so SHOULD be ok (nothing says it is tho). The thing I find strange tho is that every second cyl is rich.

8 (7)
(6) 5
4 (3)
(2) 1

 

the intake is a dual plane, ill bet the cyls that are running rich are on 1 side of the carb follow the intake passages from the rich cyls and it will point to the side of the carb that is running richer (im not familiar with big block dual plane intakes) after determining the side of the carb, hook up a vacum guage and adjust the idle screw clockwixe 1/8 turn and the rpm should pick up slightly and it will show a stronger vacum
good luck

 

Sorry I hadn't replied, bit happening. What happened was two of the rich cyl and two lean cyl were feeding from each side of the manifold. With the open spacer the two rich cyl were stealing fuel from two of the cyl on the other side of the carb. I made a divided aluminium spacer and is running right now. Thanks for your help guys.