OS 91 SZ-H-PH Hyper with pump and regulator

[mvjester]

ok I have a ? and i looked for answers with no luck. Engine is set at factory settings Mid range at 1 1/2 turns and High is at 2 1/2 turns. at hover it smokes like crazy and head speed isn't all that fast. I know its running rich cause it smokes up neighborhood. I had put high speed needle all the way in and its still rich. In the manuel it says to turn the mixture screw in 5 degrees and from there if its rich to turn the high speed needle in 4 clicks at a time. done that and its still rich. it has lag in engine almost at half stick. could someone help me on this. never messed with a 3 needle valve carb before..
Thanks,
Mark

[DavidH]

You sure you know which needle is which?

The main needle is the one next to the fuel inlet nipple. The longer needle.
The midrange needle is the one that is closest to the crankshaft end. The shorter needle.
The idle mixture is the cam screw that is located at one end of the brass bar.

The idle mixture adjustment affects the transistion of the throttle from idle to mid range.
Need to adjust the screw to a leaner setting, Turn the screw to the right about 10-15 degrees. This will lean out the idle mixture some.
Open the main needle next to the fuel inlet about 1 1/2 -3/4 turns open from fully closed.
The mid range needle about 1 1/4-1/2 open from fully closed.

Also do you have muffler pressure hooked to the tank to pressurize the tank?

Do you have the throttle linkage so that when the model is in hover mode that the throttle barrel is open to a position on one of the three marks on the carb body in the mid range?

David

[mvjester]

David,
there are 5 marks on the carb. at hover the mark matches up with the fourth mark from the closed position. I also have pressure hose hooked to muffler as well as the pump and regulator. in the book the high speed needle is the one closest to the rgulator and i have that one set at 1 turn. the other 1 is at 1 1/2 turns. and the idle mixture screw is at factory setting. at these settings it still runs very rich and it has a bog down spot just before half stick and if you go past half stick too fast the engine quits. i hope this gives u an idea as to where i am at on this carb.
Thank you,
Mark

[hanale]

Mark,

I have the same OS 91 SZ H with pump running on my Raptor 90 3D. Brand new started it up last weekend. I had the same problem at mid stick it started to bog down. If you close the mid needle to about 1/2 turn open from closed this should at least start to get you a smooth transition through mid stick. I have my high needle set at 1.5 turns open from closed at this time which I will play around with more this weekend to make sure this works the best. I did not have to touch the mix screw which is still at factory setting.

This should get you to a starting point, but monitor your engine and make appropriate adjustments from here.

[chopperben1]

Mark,

I have the same engine, started it last weekend and had the exact same issue you are having. I only spent about 1/2 hour trying to adjust, then had to go, so I'll try again this weekend.

Please post again when you solve it. I was just going to try to lean out the brass screw about 5 to 10 degrees lean from the factory setting, close the mid-range, and then open the high speed needle to 1.5 turns. I am not using fuel tank pressure, my fuel tank is just vented to air via a hose, and I read somewhere that when you are realying on only the pump, the mid-range needle needs to be closed. I am not sure though, so I'll try it and let you know.

[hanale]

ChopperBen1,

Please let me know how that turns out for you. Are you using a check valve on the inlet of the fuel tank? What fuel brand and nitro percentage are you using?

I'm running pipe pressure to the tank. I'm also running Cool Power 30% nitro fuel so I installed the second .20 mm shim into the head this weekend and it seems to run a little smoother. There's an article this month in the Rc Heli mag that talks about shims for the 90 size glo motors. Even though I'm running pipe pressure I'm going to try to tune the mid needle down to closed to see what happens. Currently I'm running the mid at about 1/4 turn open and the high needle at 1 1/2 open. The mix needle is at factory setting. My OS 91 SZ-H with pump and regulator is now transitioning smoothly through mid stick.

Take Care!

[chopperben1]

For the break-in, I am running 20% nitro. I plan on moving up to 30% in a few weeks. I am not using a check valve, as others have told me that it only slows the air flow down for no real benefit, so I am just running a piece of fuel tubing down about 1" below the bottom of the fuel tank so when inverted it won't leak.

I finally got it tuned right. Factory setting for the low-range (brass screw), mid needle closed, and high at 1 and 1/4 turn.

I guess every engine is a little different!

Good luck,

Ben

[Airboss]

my OS91pumper needles are set at 1 turn on main and 3/4 on low. cool power 30% fuel. preassurized tank. got over 5 gallons and runs excellent.