Ray,

Could it be a back cover air leak?

An air leak in the case, can produce some strange symptoms.

Bill

The holes in the spraybar are not exactly on centerline...they have to be below center, not above center. Could be the leaky backplate, but if it isn't...and checking this won't cost you that gasket set.  Steve

Sounds like you have the old style Fox NVA.  I was never able to get them to run consistently and switched to ST NVA's early on.  On the McCoy mentioned, check to see that the cylinder is in right.  Friend had one with the cylinder reversed and it ran kind of like described. 

Randy Smith can provide a Precision Aero NV assy. that's made specifically for Fox .35 Stunts. I'd suggest that you contact Randy. His NV Assy's. are absolutely the finest you can get...you'll like them a lot.

That's a good point about old glowplugs, too. I don't know why, corrosion or carbon buildup from congealed oil, or whatever...but I've had the same experience.

Also, with used engines, you never know...some folks tend to put the cylinder in backwards, or the piston and head. None of the above help anything. The bypass ports always close before the exhaust (piston rising), the baffle is always on the bypass side, and the head has to match (duh!).    Steve

The spraybar change is definately a good thing to do I have always changed them for either OS or Super Tigre assemblies, infact I have a pair of L&J reworked Fox35's and the needle and spraybar assemblies were replaced with Super Tigre ones by Larry when he reworked them, also you might want to check that there is no leaks arounf the head gasket or glowplug. As far as the backplate leaking being as the gasket is cork unless someone has taken the back plate of or the screws are loose I don't see it leaking, but I guess it could be, you also might want to make sure you are using new fuel as I had a similar problem one time at the British Nationals with moisture getting in my fuel, engine would start on a prime but would not keep running, bought some new fuel and fixed the problem, the fact you had just been running another engine I am presuming you used the same fuel so that may have not been the problem, don't forget Fox 35's should bew run on a high caster content fuel or they will just either cook or wear out very fast unlike OS engines which use less caster.
 Just my two cents
 Richard

Ray: Is your Fox the 40th aniv. model ? long needle with the spade tip ?
Are you getting fuel in the venturi ? I have a 40th aniv. model and before I put Randy's NVA in it I had to turn out the factory needle approx. 13 turns before it would run on it's own.

Finally Yes!! After 2 more hours this evening, something just happened. Changed backplate gasket , adjusted spraybar position . Nothing,  finally she started and ran really lean with needle all but falling out. Let her cool down, and for the next 20 minutes of flippin, just fired on prime. All of a sudden she took off on a super rich run and i knew it was good! Don't know the answer unless something was gummed up internally. Engine appeared to be ran maybe once before and was a little gummed up inside. This is the standard old bushed Fox 35 engine with no gimmicks. After that, i ran about 6 oz of fuel through it and ran great, back and forth from 4 to 2 and back easily. I don't like the amount of crank play, maybe that is normal for this engine. Randy, i do want to order a better needle assembly for this, no problem with the drilling part, if you would let me know what to order and any other small fix up parts. Thanks to everyone for their help. I do love the sound of this engine!!    Ray

Hi Ray,

Randy's Fox NVA needs no modifications to use.  It is the same size as the stock Fox and is turned down in the center.  It also had a nylon (or something) packing in the clamping nut which makes air leaks impossible, and locks the needle better than the ST ones..