Chevy 350 engine question/problem mystery

[Stowe, Ted-SEA]

sorry to bust in with just a average engine problem
but the smartest guys I know are on this list, so what can I say ?

I have a 350/350th in my jag xj6.
it is a '010' block, the best that I can tell,
it's a 72/73 era engine, possibly out of a chevelle or a monte carlo.

when I got it, it seemed to have a  miss and stumble at idle, not unlike an
engine with a cam. a rough idle to be sure.

since then, I've put rebuilt heads on it, I dumped the 2bbl rochester and
cast iron manifold, and put a new edlebrock quadrajet and a performer on it.

I also put a pertronics point replaclement gizmo in the distributor, and an
msd coil. I did have a problem with the new carb and I sent it back to
edlebrock to have them fix it. I have checked for vacuum leaks and have
closed off all of the vacuum lines, but the stumble or rough idle is still
there.

I adjusted the lifters properly, each one seemed to work fine, I did put
roller tip rockers on it.

compared to when I got it, the engine is smoother, but it still has this
roughness, it gets better at higher rpms.
but it is rough enough to make me put it in neutral instead of leaving it in
drive at lights.

a test taking one plug wire off at a time from the distributor tells me that
at idle each cylinder has a similiar effect to the next.

this has dual exhaust, fairly new wires, a good looking cap/rotor.

the gas mileage is awful, granted I don't have my ideal rear end ratio,
(it's 3:54) right now, and that doesn't help, but I am getting about 7 mpg.
so something isn't right. The plugs tell me that it's running rich all the
time. however from a standing start the car has lots of power, it pushes the
heavy jag right out, it's very impressive, if the power was awful I'd have a
better idea as to what's up.

I never took the timing case cover off to see if the chain is loose, I
should of done that when I had the engine out.

does anyone have any ideas ?

thanks, Ted


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