Carb manifold sealing, use phenolic spacer or not Options

[North Coast Jim]

Engine is out and I'm doing some investigations. Bought a set of Redline 40 IDFs for the engine build. They've run OK but not great. Couldn't keep lean idle set properly. drivability an issue, pops and backfires at times. Jetting changes made no difference. Suspected gasket air leaks. Should have done the starting fluid check but didn't.

While the engine is out took the manifolds off from the heads. The gasket as supplied from Redline is a thick phenolic (?) spacer with paper adhered to both sides. Found a defect in each one at both ports. Near the top of each port the phenolic has a defect - a void. The paper on each side covers the defect but does not seal the intake. Found evidence of a leak path at this area

Question - do I need the phenolic spacers ?? Can't find them on line as single replacement parts. Read of a need to keep the carbs from heat soaking but the manifolds are aluminum and are 5" tall. Don't see a need for them. Am I correct in this analysis ??

Was thinking of using .060" gaskets with Permatex red (min film deposit ) at this interface instead. What wisdom can you all impart.

Thanks for any and all input

[cpavlenko]

I had the same problem with percolation after a drive after installing Weber dual 40's. Installed the phenolic spacers between head and manifold. This helped, but now I'll give it a good drive in the heat. It's only been mid 70's here. I should have my car running by next week, temps going up to low 90's, will see how it does then. (Note) if I would've put them between carb and manifold, raintray would have to come out. Not enough clearance.