OS FS-91 - Carb Set Up - Bill Baxter
08-31-2014, 08:25 AM
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OS FS-91 - Carb Set Up - Bill Baxter
needing to set the high and low for a OS FS-91 that has sat for many years.
carb was removed and ran through crock/antifreeze to get the barrel out, etc.
The engine now starts but I don't have it adjusted correctly. High is out by about 1.5 turns and low is almost all the way out.
when go to full throttle lots of smoke from muffler.
Does not sound like it's running as good as it can.
carb was removed and ran through crock/antifreeze to get the barrel out, etc.
The engine now starts but I don't have it adjusted correctly. High is out by about 1.5 turns and low is almost all the way out.
when go to full throttle lots of smoke from muffler.
Does not sound like it's running as good as it can.
09-02-2014, 04:54 PM
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Unlike two stroke engines, very few people have a good enough ear to hear when a four stroke is running at its peak. It helps to have a tachometer when you set a four stroke up. But here is the proper procedure to set the needles either way.
Start the engine and give it a few minutes to reach operating temperature. Then open the throttle fully and adjust the high speed needle to the highest RPM that it will reach. Now reduce the throttle to idle and adjust the low speed needle until the engine is idling as fast as it can with the throttle stop wherever it is. Now go back to the high speed needle and again adjust to its highest RPM at wide open throttle. Then go back to the low speed needle and again adjust idle to its highest point possible. Keep doing this until any adjustment you make results in lowering the RPM. This is done because any adjustment of either needle influences the other needle. When you have it so that any adjustment of either needle results in lower RPM, you have it right. If it idles too fast, lower the idle speed either mechanically or with the transmitter's end point adjustment.. Now turn the high speed needle about two or three clicks rich. The engine should leave a visible smoke trail when adjusted correctly. Happy flying.
Start the engine and give it a few minutes to reach operating temperature. Then open the throttle fully and adjust the high speed needle to the highest RPM that it will reach. Now reduce the throttle to idle and adjust the low speed needle until the engine is idling as fast as it can with the throttle stop wherever it is. Now go back to the high speed needle and again adjust to its highest RPM at wide open throttle. Then go back to the low speed needle and again adjust idle to its highest point possible. Keep doing this until any adjustment you make results in lowering the RPM. This is done because any adjustment of either needle influences the other needle. When you have it so that any adjustment of either needle results in lower RPM, you have it right. If it idles too fast, lower the idle speed either mechanically or with the transmitter's end point adjustment.. Now turn the high speed needle about two or three clicks rich. The engine should leave a visible smoke trail when adjusted correctly. Happy flying.
09-02-2014, 07:47 PM
#3
I have mine set so that the low needle is just below flush. The high speed needle on mine is almost closed as in open only 1/8 turn. I beleive the previous owner screwed it in too tight and damaged the seat. Being that it runs fine this way I'm not too concerned. You may want to start at a little more then 1 turn. There is no mention of plug, when it comes to 4 strokes I only use OS F plugs. The 91 likes 15% to 20% nitro. Anything more is too much, mine did not want to run well on 30%. If you get to the point where it wants to kick the prop off then you are too lean on the high end.
