OS 40FSR- Needle required - Page 2 - RCCanada - Canada Radio Controlled Hobby Forum
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Old 08-19-2012, 04:10 PM   #11
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Re: OS 40FSR- Needle required

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Check binding on the servo and throttle linkage. Other than that you are correct in that the screw to the back will control how much the throttle closes. Back it out slowly and you should be able to get it to shut. Do not adjust it any more as that pin also guides the throttle barrel.

In some cases if the LS needle is screwed in to far it well prevent the barrel from closing.

If I remember the LS needle is backed out till it is nearly even with the outside of the barrel, but that one gets tweaked second anyway. First the HS needle is set and I normally start at 1 1/2 to 1 3/4 turns out from bottom. DO NOT get too aggressive when screwing it in as you can damage the needle or seat and affect how ornery it is to adjust. You will find this adjustment a good place to start on the remote needle, as well.

Once fired up and warmed a bit go wide open throttle and adjust the HS needle till it peaks, then open it up a couple of clicks. This should drop the RPM slightly, but helps ensure you do not go lean in flight. To help that check the mix wide open with someone holding the plane nose up. If the motor sags then you are either still too lean or you have a mechanical problem with the fuel system. Some examples are a loose or missing vent line running to the exhaust, an air leak in the fuel feed line or the tank height is incorrect. You want the centerline height of the tank to be even with the fuel inlet in the carb.

Once the HS needle is set slowly reduce throttle. Once below approx 3/4 the LS needle starts to take over and this is when you will need to be ready to adjust it with a small flat screwdriver. Unfortunately the remote needle installation does not help here except to say once set you will likely not need to touch it very often. In most cases the HS needle will be tweaked a click or two either way depending on environmental conditions. If it needs more than that you likely have something wrong, ie, the forementioned mechanical problems, a bad plug or contaminated or old fuel.

Once you have the idle relatively steady leave it there for at least 20-30 seconds, then there are two methods for testing the mixture fine tuning. One has you pinch the fuel line and see if the motor sags or speeds up before cutting out. Sagging means you are close while speeding up means you are too rich.

Personally I wait the recommended time then whack open the throttle. If the motor burps out a lot of smoke, staggers then pick up you are too rich. If it dies immediately then you are too lean. The amount of each behavior is determined by how off you are.

NOTE: The LS needle controls mixture up to approx 85% throttle, but you need to set the HS needle first as this has an effect over the entire range. If not set correctly you will find trying to get LS set extremely difficult. You may also find the motor a bit cranky until broken in.
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Old 08-19-2012, 07:36 PM   #12
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Re: OS 40FSR- Needle required

Alot of good information here.....thx
the needles I obtained got the engine running but Neither I or a flying ace neighbor could get it to set properly...I.e. must be incorrect needle.
SO......I will await the remote needle and carb plug.
many thx.
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