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O.S. MAX 40 FP carburetor settings

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O.S. MAX 40 FP carburetor settings

Old 06-10-2016, 03:13 PM
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SteveHolt
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Default O.S. MAX 40 FP carburetor settings

The original factory settings (not the needle valve setting, but the air mixtures) have been changed on the O.S. MAX 40 FP RC engine I recently bought. How can I return them to the original factory settings?

Any advice would be appreciated.
Old 06-10-2016, 04:25 PM
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da Rock
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Air bleed carbs usually have a screw that when run in closes a hole. Set it to about 1/4 into the hole while looking into it.

It richens the low end as you screw it in. It has little effect in the first 1/3 and last 1/3 so don't expect linear changes.

The unblocked area in the hole determines the amount of air available to adjust the low end. The castor fuel back then gums up things, and plugs holes.

The pinch test was a good thing to use to set those suckers (pun intended).
Old 06-10-2016, 06:40 PM
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SteveHolt
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I am familiar with settings for the needle valve to set the RPM for the motor during a flight, but there are two small black screws on the top and right hand side of the carb by the throttle arm that I need help with.

I have been led to believe they set the low and high fuel settings at the factory. Those have been turned (and the original factory settings lost) and I am not sure how to set them so the engine will run properly now. Do you know anything about how to set the two small screws?
Old 06-10-2016, 07:57 PM
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JohnBuckner
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Yes Steve the black horizontal screw is the low end mixture control screw and the one described in detail by da rock above. It functions by blocking a tiny hole directly in front of the carburetor.

Now the second small black screw is an idle stop screw. It keeps the idle from going to low to the point of the engine quitting when the throttle is lowered all the way simply by preventing further movement of the throttle. What most folks do is to bypass this anyway since it will preclude using the RC trims for throttle kill or a throttle cut on the radio.. To do this you simply back that screw out far enough to allow the throttle to close the venturi completely being careful to not go too far out relaxing the spring which may cause loss of the screw.

John
Old 06-10-2016, 08:14 PM
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SteveHolt
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John and Da Rock,

Thank you to both of you. I can now reset the screws that I moved by mistake. The information is exactly what I was seeking.

Thanks again,

Steve
Old 06-10-2016, 08:30 PM
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SteveHolt
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da rock and John,

I made both of the adjustments you suggested and now I understand the function of both screws. It is hard to see clearly the tip of the low end richness screw in that tiny hole on the front of the carburetor, but with good light, I was able to set it as suggested.

And, I adjusted the throttle low idle screw while holding light pressure against the throttle kill lever until it completely closed by adjusting the top screw. Simple and easy once you get the right help and advice.

I am grateful for your rapid responses.

Steve
Old 06-11-2016, 05:06 AM
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smeckert
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A quick google search for the manual found this link.
It shows how to adjust the air https://www.google.com/url?sa=t&sour...w0Al2FNLLs4J1w
bleed screw (low speed screw), by pointing the plane up and down while running.
Old 06-11-2016, 06:53 AM
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JohnBuckner
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Originally Posted by SteveHolt
da rock and John,

It is hard to see clearly the tip of the low end richness screw in that tiny hole on the front of the carburetor, but with good light, I was able to set it as suggested.

Steve

You are welcome Steve. Here is an alternative method for quickly presetting the low range mixture setting of any bleeder type carbs or at least the OS ones which are all identical in function from the FP's and the LA's. It is no better or worse than simply looking in the hole, both work just as well and its just a matter of what you like better.

Since I am in the habit of always keeping a 'T' pin in my tool kit (the type of pin we use in building) that I use for other things mostly. Such as poking crud out of the pressure taps on mufflers or or clearing jets. This same 'T' pin is very handy for quickly presetting the low range of any bleeder carb. Just stick the pin in the bleeder hole all the way in to the throat (back the screw out a bit if necessary to do so). Now just turn the screw back in until it just makes a bit of pressure on the pin as you pull it out -----Your low range preset is now Done

John
Old 06-11-2016, 04:52 PM
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SteveHolt
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John,

I verified the visual set with a T-Pin and found the setting very close. That seems to be a very simple way to set the low range mixture.

Many thanks,

Steve

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