helping friend with a 78' dodge pickup with a 400.

rear cylinders (7&8) are miss firing, exhaust temp around 200*.
the rest average 400* to 500*.(has headers)

comp. test showed 90# first pump,then went to 120#,on all cylinders.

he has replaced plugs, wires,cap & rotor and also put a new edelbrock (carter) carburetor on it.

i tried spraying carb cleaner around the base of carb,intake manifold and under the intake (but don't believe i was able to get the straw under very far) was not able to get the engine to pick up the rear cylinder's.

pulled the intake, tub doesn't show any obvious areas of leakage.

checked cam and lifters,all are good.

checked lifter pre-load, plunger close to bottoming.(i installed .015 shims under rocker shaft's,engine not back together yet....not sure what to do with the intake)

cleaned the intake (stock cast iron 4-bbl), with straight edge,can get .004 - .005 between the ports on the 1,3,5,7 side, and between 2&4 on the other side.

should i replace the intake?

have it surfaced?

or put it back on with the 6-pak thin gaskets on each side of the intake?

could have weak valve springs.

If the miss is clearly at idle, I would check vac to brake booster or booster itself for vac leak.

thats what I'd do is use the thin .015 gaskets on either side of the valley pan. I would mockup dry first to see how the bolt hole alignment plays out with the addition of the extra material & it may need to be milled just for that which would kill two birds with one stone on the warped potential. If I went to the expense of milling I would first put a swath of dykem horizontally across the top and bottom of the intake and head ports plus go around the corners on the ends so you can see the scribed lines when the intake is sitting in place, then scribe a line in it (top/bottom/corners) with a pointer with a 90 deg "turnup" on the corners (if that makes sense) so you can mockup & see how far the ports are misaligned (get the intake even side to side) then give that dimention to your shop so they can mill it the exact amt so the intake will set further down into the V to get the ports dead on. if the intake is down too far as is then thicker gaskets would be needed to go the other way. For cheap I would mockup & see where the bolt hole alignment falls as is & if it is acceptable (with or without paper gaskets/milling ain't cheap) then use a copious amount of some good gasket cement on the valley pan (Permatex #1 or #2 in the toothpaste like tube or "the right stuff")

we did disconnect the booster and capped intake, no difference.

don't believe its in the valve springs, motor at 1000 rpm is missing....but i can check seat pressure

thanks , that is a lot of good info.

this may sound crazy but you know what I'd try, I'd punch a small hole in the valley pan close to the suspected offending cyls & shoot some starting fluid in there with the straw to aim it close & see if it straightens out cuz if it is a vac leak its highly likely that it could be on the bottom side of the valley pan which is why it ain't showing up being sprayed on top. EDIT I reread & you are already all apart so in that case I'd go ahead with paper gaskets as is or milling and gaskets but I would mockup right now to check the alignment plus have the shop check the intake. Sounds like the down time is adding up

small hose of suitable length on a straw for the can of spray will allow you to better direct it.