OS 91 Pump Setup
Just finished this Freya and decided to try a OS91 for power, am running a Zimmerman muffler(80 Size),OS91,and a Perry Pump to maintain constant pressure to the carb.The Perry pump puts out .25 lbs of pressure per Perrys Specs.The Carb is very sensitive after adding the pump, but provides constant fuel flow, consistent runs, and does not require a ton of money to set up. The plumbing is a little tricky at first, but once you understand how it all works its actually pretty simple.Many Thanx to my anonymous friends that did the initial RnD on this setup,and burned tons of fuel getting it together.It works VERY WELL.Photos under the Diagram
NOTES: the perry pump comes w directions that show the feed point although we've been mounting em in the backplate of the 91 by installing the tap,using jb weld as loctite on the tap,putting jb weld around the base of the pump,then filling the rest in w silicone,holds real good plus no one can see the pump,and its out of the way,If for some reason the engine floods real easy always remember that the needle settings and the mixture valve settings are very finicky due to the pressure from the pump,if it is a total bitch to tune,as a ABSOLUTE LAST RESORT try turning the pump pressure adjustment in(clockwise) to reduce fuel pressure in 1/4 turn increments.
Something else we tried:
At Ron Lunds Fun Fly Curtis Y was running a
pump.He had informed me that he had removed the spring in the pump(inside
of the pressure adjustment bolt) and had stretched it to double its length
and replaced it.After doing this the engine ran very consistent,but after
he had tried adjusting the tension on the spring using the adjustment
bolt,no change was noticed during flight.That was after turning it in
flying it and turning it out and flying it.
We have been using 15% with this system and it produces good power and smooth,consistent runs.
I ran Cool Power 15% w 3 oz of oil
added and it ran very smooth,ideal for contest work.I then ran a gallon of
Cool Power 25% heli thru it and It flew better but the carb was more
sensitive,but it had a little more
I ran a tank of 30% thru mine for fun and it was so powerful its crazy.
The difference of the oil viscosity and nitro in 30% had it running with a slight predetonation condition.The easy fix for this is to add a head shim to the 91 or go back to 25 or 15%
The 91 loves to run rich so try to keep it
from getting to lean.If you adjust the needle,the mixture valve has to be
adjusted to compensate for the other adjustment
Our Engine "GURU" has his main needle set at 1 turn out in a well broken in engine and it flies smooth as glass(Freya) running 15% w a hatori sab 15(the fat 1 piece muffler)