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Old 08-14-2003, 01:50 AM
  #13  
William Robison
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Default Sterling Model Plans

maineflyboy:

In revese order, yes, the high speed needle is adjusted like any other model carb.

Initial setting on the idle speed is to let the throttle barrel shut completely, so you can stop the engine from your transmitter.

The idle disc has a notch in it, this should be aligned with the center mark on the carb body when you start. You do see the three marks on the carb body?

Set the high speed needle about 3 1/2 turns open - be careful feeling the shut position, don't force it - then with the throtltle about 1/4 open start the engine.

After it warms a bit slowly advance the throttle to full, and peak the high speed needle. No clicks rich from peak yet, leave it at the highest rpm you can get.

Slowly bring the engine speed back down, getting it to run as slowly as you can. Move the throttle trim all the way up, and see if you can bring the throttle stick all the way back. Then use the trim to bring it down as far as you can and have it stay running.

Pinch the fuel line after the engine sits at idle for a moment. It should speed up a bit, and then fall off. If it immediately falls off it's too lean. to richen the idle use a screwdriver that's a snug fit in the slot of the mixture disc and, looking from the left side of the plane, turn the disc counterclockwise about 1/2 the distance to the forward of the three marks, then try your pinch again.

If the engine had picked up a lot of rpm on the pinch you are too rich. In this case turn the disc about 1/2 way to the rear mark.

Once you have the engine just pick up a little bit before falling off with the pinch, go back to high speed, recheck the peak, and this time bring it back rich to where you would normally fly it.

Now back to idle for abot 30 seconds, and slam the engine to full throttle. If it immediately accellerates you're finished.

If it burbles a bit and then accellerates, it's too rich. Turn the disc clockwise 1/2 of one mark and retest.

If it sags before accellerating, or dies, it's too lean. This time turn the disc counterclockwise 1/2 mark and retry.

Always recheck the peak speed between adjustments of the disc.

And if this sounds just like adjusting a two needle carb, it is. But with the Perry carb the mixture disc, which takes the place of the idle needle, is more than ten times as sensitive.

This sensitivity is why some peo0le don't like them, they aren't willing to take the time to adjust them properly.

When you have the idle disc set right you should never have to readjust it again unless you make a major change somewhere.

But. Unless someone has taken it apart it should already be where it was when last flown - try it before you change anything.

HTH.

Bill.

PS I'm sure you can imagine how long this would be if we also had to adjust the pump pressure and the inverted regulator. wr.