The V8 Owners Forum -

I know this has been the subject of a couple of threads, but I'd just like your opinions:

I'm running a 4.6 with stage 2 heads & a warm cam with an Edelbrock 500 on an Offy manifold. I've got the smallest main jets in there (.077's)and the biggest (i.e. leanest) rods from the tuning pack provided by Edelbrock - and it's still way rich (about 10.9 A/F ratio at cruise).

From what I've seen on the other threads, this is much a much leaner setup than most of you run on smaller engines. Doesn't make much sense to me.

I pulled the plugs over the weekend - the even bank looks OK but the odd bank is carboned right up - they're black.

From my other thread on skimming my inlet manifold, you'll see that I'm concerned about the fit of the manifold & I'm wondering if I still have a leak on the one bank - but that will mean that it will be richer still when the leak is fixed. (In any case, I'm going to have the faces machined down to fit - thanks for your help with that one.)

I guess the other option is that there could be a blockage in the air bleed on one side of the carb causing it to be excessively rich on that side.

Anybody have any thoughts?

Blocked air bleed is one option but also check that your secondary throttle plates are closed when cruising. I believe it is quite possible that the crack open and start feeding the engine. I am running 86 jet and 6755 jets in my engine. It is still a bit rich but when I tried a leaner combo with 83 jet it started to stumble. If your engine is still rich with a 77 jet I would imagine that primary side is not the only source of fuel.

Another thought: is your OFFY dual plane manifold ? If it is, one side of carb feed both banks. So, there should be 2 sooted cylinders on both banks ?

Sondar wrote:I know this has been the subject of a couple of threads, but I'd just like your opinions:

I'm running a 4.6 with stage 2 heads & a warm cam with an Edelbrock 500 on an Offy manifold. I've got the smallest main jets in there (.077's)and the biggest (i.e. leanest) rods from the tuning pack provided by Edelbrock - and it's still way rich (about 10.9 A/F ratio at cruise).

From what I've seen on the other threads, this is much a much leaner setup than most of you run on smaller engines. Doesn't make much sense to me.

I pulled the plugs over the weekend - the even bank looks OK but the odd bank is carboned right up - they're black.

From my other thread on skimming my inlet manifold, you'll see that I'm concerned about the fit of the manifold & I'm wondering if I still have a leak on the one bank - but that will mean that it will be richer still when the leak is fixed. (In any case, I'm going to have the faces machined down to fit - thanks for your help with that one.)

I guess the other option is that there could be a blockage in the air bleed on one side of the carb causing it to be excessively rich on that side.

Anybody have any thoughts?

Sounds very strange. Where does your accelerator pump linkage go to? The middle hole or the outermost hole? I was advised to move it to the outermost hole to get the smallest squirt of fuel whenever you tread on the loud pedal.

I also had a problem with needle valve leakage, on a brand new carb, which gave me exactly the symptoms you have: black plugs. It still drove, for the few miles I did until I noticed the problem, but got real hard to start.

As mentioned by Minor V8, the Offy 360 manifold is open game to both banks so you should have soot on all 8 plugs if it is a fuel problem.

I'm ruuning a 4.6, Crane cam and heavily modified bv Buick 300 heads with an Edelbrock and it goes as good as it sounds. I'm using 086 primaries, 092 secondaries, 6347 rods and silver step up springs. Make sure your igniton is in top condition and that the spark is ok as these cabs are susceptible in that area. You may also need to swap in hotter plugs.

Thanks for the replies!

My manifold has a dividing wall running lengthways, effectively dividing it in two, each bank being fed by one half of the carb - unless there's some other fancy pipework that I can't see...

The accelerator pump is on the middle hole, but this shouldn't affect the mixture at steady part throttle.

Ignition is in good shape - it's just been overhauled & a hyfire ignition amp & associated coil fitted. The rest of it consists of a Mallory magnetic dizzy & Magnecor race wires.

I had the needles & seats out a couple of days ago & while there's nothing obstructing them I did notice that the needle on the lean side of the carb is prone to sticking shut. I'm getting replacements & we'll see what that does.

I'm also fitting a fuel pressure regulator as the Holley Red that's in there now has a max pressure of 7 psi & Edelbrock state a max of 6.5, preferably 5.5.

Sondar wrote:Thanks for the replies!

My manifold has a dividing wall running lengthways, effectively dividing it in two, each bank being fed by one half of the carb - unless there's some other fancy pipework that I can't see...

The accelerator pump is on the middle hole, but this shouldn't affect the mixture at steady part throttle.

Ignition is in good shape - it's just been overhauled & a hyfire ignition amp & associated coil fitted. The rest of it consists of a Mallory magnetic dizzy & Magnecor race wires.

I had the needles & seats out a couple of days ago & while there's nothing obstructing them I did notice that the needle on the lean side of the carb is prone to sticking shut. I'm getting replacements & we'll see what that does.

I'm also fitting a fuel pressure regulator as the Holley Red that's in there now has a max pressure of 7 psi & Edelbrock state a max of 6.5, preferably 5.5.

My mistake, the Offy 360 does have a central divider, effectively cutting the manifold down the centre. I have one sat in my garage.

The accelerator pump shoves a squirt of fuel in every time you open the throttle, so it may be drowning the motor enogh to blacken the plug, but should do it to both banks by rights. I'd leave it where it is until you have the new needle jets in place, then drive it again. If it has got no better then move the pump connection over to the end hole, see if there is a difference. Don't do both together else you'll never know if it was needle valves or accelerator pump that was the problem.