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.45 ABC Mid range problems

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Old 04-17-2002, 05:20 PM
  #1
hebertjj
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Default .45 ABC Mid range problems

I have a ST .45 ABC that's giving me fits running in the mid range. I'm running club 15% fuel, MA 10x7 prop, and a Thunderbolt R/C plug, and it loads up running in the mid range and won't transition well from idle to full speed. I've even tried rotating the spray bar a little since this is adjustable on the ST carbs; where is this supposed to be set? With the fuel nipple horizontal or at a slight angle? Any majic fixes for STs you know of?

This engine really looks well made and is powerful at full throttle, so I'd like to see it running well.

Thanks for the help and all the trouble shooting you do,

Joel

P.S. What would it take to get you in trouble so that you'd lose your job, and I could take your place?
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Old 04-17-2002, 05:58 PM
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amcross
 
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Default .45 ABC Mid range problems

Hi agin joel! thanks for starting a separate thread, its far easier.

To properly set up your carburetor, there are a few steps...

Make sure the spraybar is set so that the fuel slot is pointed straight down the center of the carburetor. You will have to look through the carb from the bottom, with the venturi opened to full. Loosen the two screws next to the high-speed needle valve to rotate the spraybar so that the slot is centered.

The idle needle can be seen in the slot of the spraybar. It looks like a piece of wire that has the end squarely cutoff. It should be less than one-half way across the slot when the venturi is opened to full.

The high-speed needle should be opened about 2-1/2 to 3 turns out from closed.

All of these settings are very rich. You'll have to start the engine at about 1/4 to1/3 throttle. Once the engine starts, advance the throttle to full. You can then lean the high-speed needle until the engine is running just rich of peak RPM.

Once you have the high-speed needle set, you can retard the throttle a bit and use the idle needle to adjust the engine. Retard a bit, and adjust. Keep doing this until you have reached the desired idle RPM and mixture. Remember, since we started out with an intentionally-rich setting, the idle mixture will have to be leaned.

Finally, the midrange can be adjusted by rotating the spraybar a hair. Just loosen the two screws next to the high-speed needle and rotate the spraybar just a tiny bit. Either direction is OK. This will help you get a good transition and midrange.
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