Engine help near Lancaster PA

Depending on the version of engine, Cox International has needle valve springs, for example:

http://coxengines.ca/cox-.049-.074-needle-valve-spring-3.html



So does Ex Engines:

http://www.exmodelengines.com/cox-.049-needle-spring-3.html



Not saying those are the ones you need, but they have others.

Usually when the needle turns on it's own is because the little rubber piece is dried out. The spring does help, but that piece of tubing also keeps air from leaking past the needle.

I've done both. Not familiar with what specific version of engine came with that particular Cox RTF. Seems to be an as case basis. Worst needle set up with the OK Cub .049's I've got. They have a sleeve over the needle valve assemble that has a slit on both sides with a tapered blunt tip needle. I put a section of small silicon fuel line that covered the slit and spray bar, which helped, but still needle was a bit touchy for my comfort. I'm sure he'll get it sorted out.

GallopingGhostler wrote: ...Worst needle set up with the OK Cub .049's I've got. They have a sleeve over the needle valve assemble that has a slit on both sides with a tapered blunt tip needle. I put a section of small silicon fuel line that covered the slit and spray bar, which helped, but still needle was a bit touchy for my comfort. I'm sure he'll get it sorted out.

George,
Many OK needles only have a blunt end that provides a slobbering rich to full lean in less than a turn. For these I file (or sand) some taper on about 3/8" to 1/2" of the needle.

George

Fit and finish on the Cub wasn't that great, needle had a little wobble to it, which didn't help. A simple wiggle would cause mixture to change drastically. I haven't tried the filing fix yet, George. I'm almost tempted to JB Weld a Cox NVA to one.

Given the quality control issues, I'd understand why Cox surely dominated the market. Every new Cox reed valve engine I purchased ran right out of the box, and ran good until I crashed. Wash the dirt off, clean back screen. After a season of running, devarnish the cylinder, back in business.

Cribbs74 wrote:Usually when the needle turns on it's own is because the little rubber piece is dried out. The spring does help, but that piece of tubing also keeps air from leaking past the needle.

Cox International has these-

That's fine if using a non-tanked backplate.  The tanked version has no seal, but as already mentioned, you can use a small piece if fuel tubing to seal the needle.

Thanks for all the help and ideas, folks! After some fine tuning we were able to get the engine running reliably. Also, since this is the older style model with a fuselage held together with rubber bands, we simply ran a rubber band around the needle valve. It naturally ran right beside the valve so there shouldn't be an over abundance of torque on the needle valve I shouldn't think. Maiden voyage scheduled for today!

On the Tanked Cox engines I find it useful to first put on a well fitting flat (usually #2) washer, then cut the fuel tubing to just a hair longer then the normal running setting so there is a slight compression of the tubing... no washer and the tubing does not seal and also vibrates up the Needle to the knob

For the non tanked, the hard rubber items shown above, are the ticket... they are NOT threaded so the first use demands some effort to fully seat the needle...caution!!!! this first use is very hard and "feeling" the needle bottoming out is hard to detect

If you go too far you WILL damage the needle and it seat

Before I do this I take the loose needle and get it started withOUT the new hard rubber piece...., and carefully COUNT the turns in to fully seated...then install the new holder/seal and stay one full turn less than fully seated..... ( hint the typical running setting is 2.5 to 3.5 turns OUT)

These dinky engines are finicky...don't create problems... as Rusty has posted about a hundred times...CLEAN/CLEAN/CLEAN and then if not sure clean AGAIN!