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Model Forum / Radio Controlled / Air Models / November 2007Cox engine problems
I have a Cox Queen Bee .074 engine. It never ran good, it has been in storage for 6 years, now i want to make it work right. i can get short bursts out of it but thats it. I have checked everything. i have tried priming via exhaust, thru carb, cleaned entire engine inside and out, new glow plugs.... I dont know what else to try. i think it has a lot to do with compression. i can see fuel bubbling out from the piston/cylander when i have the muffler off. is there any way i can improve compression on this engine? I know its not a very good model, but i have it and i know it will run if i spend enough time on it. Thanx for your help,  SignatureMatt C. amgock@nospam.netzero.net --remove no spam... Matt, a couple of people chimed in asking for a few details last time you asked this a few days ago, but you never replied. Jot down the basics - type of prop, type of fuel, etc. for starters. Describe your tank setup too. How long is your fuel line, is the tank higher or lower than the carb, etc. These are important for any kind of suggestion or diagnosis. It is not unusual to see bubbles as you turn a lapped piston engine over slowly by hand - there is always a little blowby. Does it bounce and "pop" when you flip it over hard (with some oil in the cylinder)? If it will run off a prime, but not continue running, it sounds like fuel draw issues - carb problems, air leaks, you name it. Does it run off the prime fast then starve for fuel, or does it load up and die rich? Mike D. > I have a Cox Queen Bee .074 engine. It never ran good, it has been in > storage for 6 years, now i want to make it work right. i can get short [quoted text clipped - 6 lines] > run if i spend enough time on it. > Thanx for your help, > Matt, a couple of people chimed in asking for a few details last time you > asked this a few days ago, but you never replied. [quoted text clipped - 13 lines] > > Mike D. 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, Bill > > Matt, a couple of people chimed in asking for a few details last time you > > asked this a few days ago, but you never replied. [quoted text clipped - 39 lines] > Thanx to all, > Matt 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. > Matt, > [quoted text clipped - 9 lines] > > Bill 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. -- Paul McIntosh http://www.rc-bearings.com > 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 [quoted text clipped - 16 lines] > > > > Bill 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! SignatureMatt C. http://home.comcast.net/~briarbushbrewery/ > 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 [quoted text clipped - 26 lines] > > > > > > Bill Glancing back at http://www.mh-aerotools.de/airfoils/cox_frameset.htm, 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 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 |
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