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HomeAircraftHelicopterMain Discussion › How to do an OS 70 SZH needle setup?
11-02-2004 01:08 AM  13 years agoPost 1
jackheli

rrProfessor

Vancouver - Canada

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Hello all,

I have about a gallon and a half on my OS 70 and thinking of leaning it out. The break-in was done at factory settings which provided a rich and cool run.

I have only had two needle carb engines so I am unsure of how to go about fiddling with the three needle OS carb. Do the needles interfere with each other? Which needle should be set first? I've heard that on the OS I should start with high-end needle, doing climb outs.

Please help. Thanks.

It's easy to find an excuse to do wrong. Hard is not to find an excuse to do right.

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11-02-2004 03:50 PM  13 years agoPost 2
Mike Wilson

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Toronto, Canada

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Jack,

I had one of these engines and I found them very easy to tune. I was using a KSJ 90 sized muffler and Magnum 30% fuel.

The first thing you want to do is set the low speed needle by doing the pinch test to ensure that the low end is not too lean. You should be able to pinch the hose to the carb and have the engine run for aprox 3 to 4 seconds. You will then want to tune the high speed needle by doing climbouts until you feel that the engine has the power that you want. I would suggest that you do a few climbouts and then land and check the backplate temperature. You should be able to keep your finger on it for at least 3 seconds. Also look for a smooth smoke trail. The amount of smoke will vary with fuel brand but you should see a consistant flow. Once you have the high needle set, you can then set the mid needle by hovering the heli and watching the smoke trail as well as the feel of the heli during hovering. It should not feel sluggish and should have a decent amount of smoke from the exhaust. You will also want a consistant transition from low to mid to high as well so adjust the mid needle until you get a smooth transition without seeing any change in the exhaust.

.....led

Teambob00

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11-02-2004 08:21 PM  13 years agoPost 3
jackheli

rrProfessor

Vancouver - Canada

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Thanks.

I'll start from the factory settings and go from there as you said.

Cheers.

It's easy to find an excuse to do wrong. Hard is not to find an excuse to do right.

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11-03-2004 10:08 PM  13 years agoPost 4
Jamovich

rrVeteran

Bangalore, India

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hehehe
Do it my way...heli held over head....70 size..preferably 2 ppl holding it while you tune. If u wanna feel slightly safer use a hardhat!!


Jamovich

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11-04-2004 01:17 AM  13 years agoPost 5
jackheli

rrProfessor

Vancouver - Canada

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Jamovich,

I trust you don't have long hair...???

It's easy to find an excuse to do wrong. Hard is not to find an excuse to do right.

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