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Old Apr 07, 2014, 06:35 AM
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Help!
unable to get cox motors to run

hi guys,

I started with cox motors and control line many years ago (flying guillows kits). over the last year or so I've picked up a few new motors and can only get my throttle version one to run. the other three sure starts only fire and run in a brief spurt....this includes the motor on a new/old production cox pt19 I picked up on ebay. using a new hobbico 1.5v battery, new cox super power fuel, and have checked glow plugs, switched fuel tanks and lines, and everything else I can think of. the manuals say to start the starting process with the valve open four turns, and I've tried a turn or two in either direction but still only get the same brief spurts of run time.

this brings back a lot of memories of fooling with these motors! I think back in the day I only had one (our of several) that would run reliably. nice to see how easy things have become these days with our electric set ups....

anyways, if anybody has any ideas i'd love to hear them! thanks for your help!
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Old Apr 07, 2014, 07:55 AM
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Usually the reeds gets dried castor on, and don't seal. This can be remedied by dribbling a couple of drops of fuel through the hole in the backplate. Sometimes the pickup tubing gets real hard and cracks, or the needle valve and the little hole get clogged. If you don't want to take the motor apart, you can fill the tank and plug one filler hole and squirt fuel though with a bit of pressure and repeat with the needle out. I would just disassemble it and check everything, being careful of the backplate gasket, and checking the O ring. Having said that, it usually takes a few runs off of prime to get them feeding right. 4 turns doesn't sound outrageous.
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Old Apr 07, 2014, 08:31 AM
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so, disassemble, check, clean? didn't consider this since the motors were new (although possibly many years old) but it can't hurt. thanks for the suggestion, i'll try this later today. funny, the only one that runs is new production so you may be on to something as far as the others being gunked up.

thanks.....rob
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Old Apr 07, 2014, 10:32 AM
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I recall my Cox .049's needed 3 1/2 turns out to start.
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Old Apr 08, 2014, 04:32 PM
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Rob, I'm not sure if you've heard or read, but the new Cox fuel being sold by Tower Hobbies is terrible for the Cox engines. The Cox engines need at least 20% castor oil in them. The new Cox fuel sold by Tower only has 1.8% castor in it. I'd add a good bit of castor to your bottle, or just get some fuel with a guarantted castor content of 20% or better.

Mark
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Old Apr 08, 2014, 06:17 PM
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I would agree, 20% castor is a must. I use Model Technics GN25 Nitro Mix - contains 20% castor oil with nitromethane only as the power and tractability additive. This is the range demanded by the traditional modeller and is well tried and tested.
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Old Apr 09, 2014, 05:06 AM
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wow, I had no idea about this fuel! I thought by buying cox I was getting the right stuff. i'll look for what you guys have recommended (I think sig makes it). thanks.....rob
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Old Apr 09, 2014, 10:34 AM
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Thanks for info on Cox fuel. Pretty sure in the dark ages it had the higher castor amount. any idea on why the change?
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Old Apr 09, 2014, 12:45 PM
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I found sig "champion 25," here's the formula:

25% Nitromethane
20% Lubricating Oils
(1/2 Castor, 1/2 Klotz)

I seem to remember using this a few years ago and getting decent runs (at least on the bench).

it's not entirely 20% castor but would this be ok?

thanks again.........rob
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Old Apr 09, 2014, 02:36 PM
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Just make sure you have a strong 1.5v current these cox glow elements tend to need more than a standard glow plug on 1.2v nicad type cell. That and a electric starter should help even the most fussy engine.
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Old Apr 09, 2014, 02:55 PM
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Hoppes #9 gun cleaning solvent and a basic gun cleaning kit are good to have for .049 maintenance.
Plastic bristle bore brushes and rags come in the kit.
A cheap plastic jeweler's lens is an interesting "tool" to have. Not so much a tool, but it will reveal flaws in small parts that the naked eye can't.
Also a Monoject 2 oz veterinary syringe with a short piece of 3/32" brass tubing pressed into the tip is useful for fueling, blowing out / sucking out / troubleshooting fuel lines and "pressure washing" dirty engines at the field.
most of my problems with reedies have been grass seed and hairs collecting at the intake screen or at the reed. The reed has to be free to bounce back and forth inside it's little enclosure and it doesn't take much foreign matter to disrupt it's movement.
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Old Apr 09, 2014, 05:47 PM
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Quote:
Originally Posted by combatpigg View Post
most of my problems with reedies have been grass seed and hairs collecting at the intake screen or at the reed. The reed has to be free to bounce back and forth inside it's little enclosure and it doesn't take much foreign matter to disrupt it's movement.
+1

It's surprising how stuff can find its way between the reed and seat but not find its way back out. Doesn't take but a small piece of schmutz to keep the reed from seating and she no run....
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Old Apr 09, 2014, 07:33 PM
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Originally Posted by combatpigg View Post
............most of my problems with reedies have been grass seed and hairs collecting at the intake screen or at the reed. The reed has to be free to bounce back and forth inside it's little enclosure and it doesn't take much foreign matter to disrupt it's movement.
I've had grass seed problems, too. Hard to figure how a seed can work it's way up the intake groove in the back plate, down the venturi and lodge under the reed.
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Old Apr 09, 2014, 10:19 PM
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I always figured the flight goblins put them there. I've flown the old golden bees which had the screen over the intake on a concrete parking lot and still got stuff in the reed. I don't think even a K&N filter would stop it. So I just figured it was the same goblins from the old twilight zone episode with William Shatner that did it.
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Old Apr 11, 2014, 01:36 AM
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Quote:
Originally Posted by hllywdb View Post
I don't think even a K&N filter would stop it.
K&N filters are terrible for anything other than performance engines. They let way too much stuff through when compared to traditional paper or foam filters, IMO. Sure they breath better, meaning better performance, but unless you're ready to do a rebuild (as most race teams are), then you're not likely doing yourself any favors using them. Just an FYI.
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