The carb has an insulator bushing that should seal on the manifold and mine are both brand new, but wondering if I could apply some sort of sealant on the manifold that would form an airtight seal? What would be recommended?
If you wanted to try a sealant, why not try same Hylomar or Permatex Ultra Gray or some of the other sealants used on the cylinder base. It's designed to work with heat and with a thin even coat, it should be able to form a seal.
'78 R100/7 '69 R69S '52 R25/2
92 R100RT/69 R69S
2004 Aprilia Atlantic 500cc single cylinder Scooter
83 Honda V65 Magna, fastest production bike in1983
yes, the Dellorto's are different in that there is no rubber connector between the carb and manifold. The manifold's are unique to the R90s also, due to the larger Dellorto's.
See the image, where #4 (insulator) is the part inside the carb that forms the seal around the manifold.
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That still didn't work so now I'm thinking of using a very thin o-ring to slip over the manifold that will allow the carb to slide over that.
Better yet might be to machine a recess into the intake manifold to "hold" the o-ring.
I'm glad I found the air leak as it explains the high idle I've been fighting for a few years, but at the same time, this sure is frustrating.
Maybe the manifold is oval from being tightened with a pipe wrench or similar?
69 R60/2 76 R90S 78 R100RS
70 Triumph w/Spirit Eagle Sidecar
I learned the following:
apply a thin bead (carb detached) and let it skin for a few minutes
assemble carburetor over the manifold WITHOUT tightening the clamp
wait 24 hours
Start motor and check seal with carb cleaner
Verify that rpm doesn't change
I rode her to work today (120 mile roundtrip) and no issues whatsoever. Even after sustained 80mph on the freeway, the bike idles at a nice, even 1000 rpm.
Note to self: Ride this bike more!!!