I have a 460 in an `85 F350. It has all the emissions equipment removed and recently I installed an Edelbrock 1406 carb.

With the old Holley the plugs all looked about the same in color and indicated that the motor was running on the lean side. I have just pulled the plugs since installing the 1406 and find that four of the eight plugs are very rich and the other four are on the normal to lean side. The four that are rich are the front four cylinders. That is, the two front cylinders on both banks.

I can not figure out how only those four cylinders could be rich while the four seem fine. I do not seem to have any vacuum leaks while having consistent vacuum reading in the 19” to 20” range.

Any thoughts would be greatly appreciated.

Thanks,

Mark

 

Did you check the intake channels for any kind of buildup or blockages?

 

I thought that I might have a vacuum leak and decided that I may not have an over rich situation as much as a lean one.

Took starting fluid and started spraying and found that when I sprayed where the carb spacer meets the manifold, on the back side, I had an air leak. Yanked the carb and found that the gasket that I used between the manifold and the carb did not completely cover a passage (not sure what the passage is there for) that allowed air to be sucked in on the driver’s side.

Once I got the carb off it looks to me as if the manifold is not completely open but rather the diver’s side of the carb – primaries and secondaries - feeds the rear four cylinders and the passenger side feeds the front four.

Based on the way the truck ran after installing the Edelbrock, I enrichened mixture with jets and metering rods. This served to over enrichen the front cylinders and provided just enough to the rears so that they were not overly lean.

With a new base gasket and putting the carb back to the original specs I should be fine.

Thanks,

Mark