Cox engine problems

Im sorry about the last message, i never knew it was even sent, my newsreader was acting funky that day...but i read the postings, thanx to all who chimed in.

heres the problem now- it will run at full open throttle continuously. when the throttle is backed off it starts to sputter and will die if i dont work the throttle right. I need to work on my low speed idle screw to correct this as well as needle adjustments. i think my needle is bent just a bit, and this is causing mixture problems, i will replace it or try to fix it. Also the needle seems to unscrew itself as the engine is vibrating... maybe a little threadlock?

The prop is a nylon/glass Tornado 6x3p. I have my glow plug running a little hot, at 1.63 volts to get quicker starts. I am using crappy fuel though, it isnt a high enough nitro content, but it will run.

My tank is placed just below the needle and about four inches back. I have the carb ported to help pressurize the tank, but it seems to not be necessary.

anything else?

Thanx to all, Matt

Matt,

You said it yourself.... "crappy fuel" These littls engines need nitro... Run at least 25 to 30% nitro, castor based fuel...

You may be able to help the needle vibrating problem with a short piece of fuel line place over the needle. Make it long enough that it "squishes" a bit when the needle is in its operating range. This will help to absorb the vibration...

Cheers,

Yep, what Bill said. Too low a nitro content or substandard fuel in some other way will most definitely cause you grief as you try to throttle a small motor. It's enough of a challenge without fuel issues!

Mike D.

And pay attention to the castor statement. The piston to rod connection is a swaged ball and socket affair and is very sensitive to low oil content and definately likes a lot of castor.

Thanx Guys. I appreciate the help. I changed fuels and adjusted the idle and it is running good for me now. I don't really like this motor, but until i find something else cheap enough im gonna make it work. By the way in case any were wondering i am going to use this on a small foam/fiberglass airboat i am building. Thanx!

Glancing back at

see that you have an interesting and unusual engine, for a reed valv anyway. The Cox reed valve engines are generally a lot less fussy tha the TDs. If I saw bubbles between the head and cylinder, when it was tight an clean, I might try 1500 sandpaper on the head and head gasket. If the compression is really bad, it will go dead instead of bouncin forward or backward when you flip it over slowly, but if it starts on prime and dies, then I agree it is more likely getting too little or to much fuel. Too little is more common. With too much fuel, they slo down and stop, maybe spitting raw fuel. With too little they reach high note and then stop more suddenly. Could be it is still not primed enough. Can you blow through th needle valve opening? Do you have instructions how many turns to ope the needle? 2 1/2 to 3 1/2 turns from closed is typical. Sometimes i takes me a while to start a Cox reed valve engine that hasn't been ru in a while, maybe a matter of getting it fully primed

-- david.ingha

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One more possible suggestion. I have had a number of Cox reed valve engines where the needle valve had been damaged by over tightening. If you back the needle all the way out and run your fingernail along the tapered part it should be very smooth. If there is a lip or edge near the middle of the taper it was caused by overtightening the needle. The best solution is to replace the needle. This does not happen as often with the engines that use a seperate tank but is a common problem with those with intregal tanks. Bob Furr