Some folks sought my opinion on an issue raised above. In my experience, the only reliable repair for fuel/air leaks at the plenum halves is replacement of the plenum seal. Typically, it’s wise to renew the carb-to-plenum FUEL seals as well as the large “AIR” orings at the same time.
High quality rubber components such as plenum gaskets, carb-to-plenum, orings etc. last indefinitely, but when disturbed - most professional mechanics consider it a “best practice” to renew them. Skipping replacement is generally a false economy since so much labor is required to gain access. “Come-backs” are death to a pro mechanic.
Permatex Aviation Form-A-Gasket No 3 Sealant is an excellent product. It has useful chemical resistance, temperature and pressure characteristics. For years, I’ve used and recommended it for tasks such as sealing the threads on fuel tank drain plugs as mentioned here: http://www.randakksblog.com/fuel-tan...t-get-kreemed/
According to Permatex ....that product is intended for “close-fitting parts, machined surfaces and threaded connections.” It’s marketed for “close tolerance flanges” and similar applications. It is not ideal where there are large voids, lots of manufacturing “slop” and a minimal number of clamping points ....as in the case of plenums. One of several improvements we made in our latest plenum seal design involved accommodating the wide range of actual dimensions for the plenum seal groove found in the field.
Worse - the thin viscosity LIQUID migrates easily. That has bad implications for the air / fuel passages coursing through an early GoldWing plenum. They can easily be compromised. I’ve seen numerous cases where errant sealant debris made its way to the float valves and caused havoc there. Plus, the next mechanic who revisits such a “repair” will not appreciate the huge, unnecessary mess it makes!
Plenum gaskets are readily available from Honda (nitrile), Saber Cycle (nitrile) and our own VITON version (referenced above). My experience - installation of a proper engineered, formed plenum gasket would be preferable and more reliable than any attempt at repair by a sealant product.
Be aware that there are MANY grades of nitrile (aka BUNA) and VITON available. The materials and manufacturing processes affect the resultant performance characteristics over a rather wide range. That why we use only an automotive grade of VITON (same grade as selected by top auto makers for fuel system use.)