I have been assisting a friend in restoring his #7 Johnson Rocket, aka
"The Great Pumpkin". It had the O-435-1 (O-435-C), with the MA4-SPA
carburetor. He had had the single-piece venturi installed when he bought
the plane.

It would cough and miss when power was reduced to 20" MP, making it
unsafe to fly.

In talking to El Reno Aviation and the Stinson Sentinel group on Yahoo,
I found out that the single-piece venturi makes the MA4-SPA completely
unusable in the O-435. I have been operating, under field approval, the
MA4-5 for the O-435-A engine on the O-435-C, for the last 25 years.

I also had a core carburetor and sent it out for overhaul/updating. We
installed it on #7 (with field approval). I flew it today for the first
time and had flawless engine performance!

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