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twinman -> St 90-More power!! (1/26/2002 7:11:50 AM)
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Check your spray bar. The earlier engines used a flat spray bar verses newer ones that are round. You can file the round one, but do not go into the fuel passage or you can pay up to $15.00 for a ruined spray bar.
To determine spray bar identification
1. The standard spray bar is completely round as you look down the carburetor. The bar is a uniform .155" in diameter.
2. The preferred bar has flat sides milled on each side .098" across and .336" long from the end.
3. I believe that it would be possible to modify a standard spray bar to those dimensions relatively easy. WARNING: If you grind too deep, you will break through to the fuel passage and ruin a perfectly good $15.00 So be careful!!!!!! This is brass!
This, on a 13x6 prop was good for 400 RPM on a piped ST 90
My piped and old ST 90 turns 13000 with 15% with above carb.
I changed to an ASP 108 carb,which is a clone of the OS 7D, but half the price. Note, some of them have a restrictor sleeve. Remove it! I gained 600 RPM, yes with a pipe!!! and Tach. Same day, engine and fuel.
This was too fast as it screamed on the dives. Changed to MA 14x6 and hit 12,700...for two years so far.
I prefer synthetic only as I had problems with varnish at these performance levels. This works and the engine lives is still running with I have no idea how many gallons of fuel.
My two cents!!
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