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Cox Engine of The Month
November-2024
Kim's

"A Space Bug Jr. pulls the Q-Tee up high over Sky Tiger Field"



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Post  batjac Sat Jun 08, 2013 7:16 pm

I'd seen pictures of the throttled Medallion .049 like in the Reviews thread, but I'd never seen one in person. So when one came up on eBay last month I went ahead and got it. Man was that thing ugly. It was dirt covered and frozen up, but after an evening of work it was flipping over nice and easy. I thought about polishing it up, but didn't want to pull the polishing stuff out until I was sure it was a runner. I also added a spring starter that I got from Bernie.

Yesterday I set it up on the test stand with a 6x3 prop and fired her up. AWESOME!!! I couldn't find my tach to check the prop speeds, but the Review section article says it throttles down to 1700 RPM and I believe it. And it was a reliable idle, too. I closed the throttle off all the way and let it idle for a whole minute, and it came smoothly back up to full RPM. When I get my tach, I'll see what the Full and Idle RPM's are, and swap out for a 5x3 prop and see what that throttles to. Too bad these aren't for sale anymore. If another throttle assembly comes up on eBay again, I'm gonna get it for my other Medallion .049. Blows the Ace throttle sleeve out of the water. I have the Sure Start R/C throttle on order from Bernie so I can compare idle RPM's, but that's really an apples to oranges comparison. I have to finish up that Q-Tee I started 20 years ago so I can put this Medallion on it. Clapping

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Post  RknRusty Sat Jun 08, 2013 7:47 pm

Wow, that cleaned up really nicely.

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Post  bullit132 Sat Jun 08, 2013 7:48 pm

nice,ive never seen one of those Small Cox Logo
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Post  Surfer_kris Sun Jun 09, 2013 7:28 am

They used to sell conversion kits with everything needed, i.e. muffler and spray bar etc, both for the .049 and .09. Would be nice to see these conversion kits back in production. Here is an .09 that I've "converted";

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Post  Kim Sun Jun 09, 2013 7:45 am

Nice Restoration !!!!!!!!!!!!!!!!!!!
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Post  coxaddicted Sun Jun 09, 2013 8:26 am

I know these valve throttles, they are working better than their reputation.

Here is one on Ebay:
http://www.ebay.com/itm/Cox-Rc-engine-/111088472355?pt=US_Radio_Control_Control_Line&hash=item19dd639123
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Post  kevbo Tue Jun 18, 2013 2:18 pm

The operation of the exhaust valve is clear. I am a little unclear on what is going on with the the intake part of the show.

This is my guess from the pictures:
It looks like there is nothing to restrict the intake air as the spray bar rotates. The spraybar has a wide cut instead of just a jet hole as normal. By rotating the spraybar, the needle/seat vacuum signal varies depending on the angle the "jet" cut is making to the intake air, and this approximately corrects the mixture as the airflow varies due to exhaust restriction.

Do I have that right?

About what angle is the sparaybar flat when the trottle is wide open vs. idle. Maybe if I could impose on you to take some closeups of the spraybar showing how the flat aligns with the control lever I could work it out...but maybe you don't want to risk losing the circlip!
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Post  batjac Wed Jun 19, 2013 1:23 am

When I get the engine back on the bench I'll see if I can get any good pics of the spray bar in the high and low throttle positions.

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Post  Surfer_kris Wed Jun 19, 2013 6:19 am

The flat part is paralel to the flow of the air at full throttle, and it restricts the airflow a little at lower settings but not as much as it would have to on a regular intake throttle without an exhaust restriction. The exhaust restriction would be enough for throttling on its own, but the intake needs adjustment too inorder to not loose all the fuel draw at the lower airflow, I guess.
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