Jamie, just for giggles you may want to try it with the r/c carb. I run several like that with no problems, just wire the throttle open. May need to adjust the tank height to run upright and inverted.

The 15 IV is a good engine. It is an Iron piston/Steel sleeve engine. Make sure the fuel does not have less than 20% Castor oil for lube. It does not need more than 20% Castor unless you go to 25% or more Nitro. If you use the right fuel the engine will last forever. Do you know how much time is on the engine? If it has less than 2 hours on it, it may not be broken in. 

Pat

       Jamie, I found the 3303 not to be control line friendly. The head is slightly smaller than the 3304 and there is also web castings in the exhaust stack. I think the main problem with the 3303 was getting rid of the heat. I never tried the 3304, but I always felt it would do well. I would recommend the use of a prop like a 7x6 and let it turn up. The main problem with these engines is unlike the r/c crowd, were running our engines flat out. The stock mufflers are not good . They retain too much heat and have to small of an outlet hole. My 3304 is unrun and has the same muffler as my 3303 did. I opened the exit hole up to the point I was almost breaking out of the casting. I experimented with this engine for nearly two years trying to get a steady run from start to finish. In the end of the flight it would always go overlean and run away. I went to a uniflow tank which helped but I found a Randy Smith tongue muffler worked using the strap from the stock Enya muffler. I used the tongue for the FP.40. It didn't fit perfectly but good enough. This really helped keeping things cool. Ken

The thing about the old Enyas at least, seem to be that when you think they should worn out, they are just getting broke in.  I have a couple that are easily over 45 years old and they run like a top.  25% or so castor in the old iron piston Enyas, plenty of cooling allowed, and somewhere in the 4 to 4 1/2  or 5 pitch on the props.  Most of the older ones in the .15 to .35 size are better suited to a wet 2 run like modern engines.  My old Enya .35 with the multiple insert "square" venturi is pretty strong, and been in my possession since about 1965....... give or take a year or so.  It will do a decent 4-2 on a 10-5 wide prop if treated right.  Smallest venturi insert and low compression head (it came with two heads and three venturi inserts).

Big Bear