Get rid of those fuelers. I've had nothing but trouble with them. Want some more?

The rings wear and become lodged in the lines, etc.

Use a T connector and fuel dot instead. Much safer.

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I recently put a slightly larger muffler on an O.S. 1.20 after I was having similiar problems with it's smoker, just as you are.

I tried the wrap technique but I was not quite pleased with the results. The muffler still tended to cool too much in flight.

Instead I coiled copper tubing INSIDE the muffler, to act as a heat mass and at the same time act to provide far more surface area for the oil to heat up from.

It worked great! The output from the engine keeps the copper HOT and it does not cool down in flight.