Pathway Restriction

Should I reduce the restriction where the carburetor manifolds meet the head? If so, will something good happen?

I'm guessing the opening drops from 36mm (carb ID) to 30mm +/- at the smallest hole diameter of the manifold. There is a well-defined lip there, but I fear that modifying it may create a problem...

You need to blend the manifold to the inlet tract to eliminate the step.

zed1015 wrote: You need to blend the manifold to the inlet tract to eliminate the step.

Best tool(s) to use for that? I have a round rasp file, and a spindle sander...

I use carbide burrs and a flexi drive but hand held files will do the job just fine if the person doing the job is competent enough.
It will just take more time doing it by hand but being aluminium it won't take long.

zed1015 wrote: I use carbide burrs and a flexi drive but hand held files will do the job just fine if the person doing the job is competent enough.
It will just take more time doing it by hand but being aluminium it won't take long.

The oscillating spindle sander method...
With the removed carb manifold upside down on the flat table surface, its easy to sand off the rubber right up to the visible impression created by the edge that the intake runner formed in the rubber surface. A must to reattach the manifold in the same carb location it was removed from, for a good re-seal. The resulting inside rubber surface is smooth and flat!

daveo wrote: The oscillating spindle sander method...
With the removed carb manifold upside down on the flat table surface, its easy to sand off the rubber right up to the visible impression created by the edge that the intake runner formed in the rubber surface. A must to reattach the manifold in the same carb location it was removed from, for a good re-seal. The resulting inside rubber surface is smooth and flat

AH! It wasn't clear that you meant opening up the inlet rubber and not the aluminium tract in which case your method is ideal and I don't use files or burrs for that.
Usually I fit the rubbers and trim the lip in situ to match the head.
Your step up in diameter from smaller inlet rubber to larger inlet tract is not as detrimental as the fuel meeting a step in the alloy where the tract diameter is smaller than the rubber which could cause unwanted turbulence and possible minor (although probably undetectable) flow restriction at full bore.
Either way, a smooth transition for the fuel path is always favourable.

A notable difference, and worth the effort to correct

As before and after

Thank YOU zed1015

years ago my brother took a steel shaft that was the size he needed and heated it with a torch then took the manifolds an slide em on the hot shaft. kinda smoky but it worked great.

eddiem wrote: years ago my brother took a steel shaft that was the size he needed and heated it with a torch then took the manifolds an slide em on the hot shaft. kinda smoky but it worked great.

:ohmy:

daveo wrote: A notable difference, and worth the effort to correct

As before and after

Perhaps...perhaps not. :blink: