Hi Dave;
I set up several FP engines with the original rear needle valve that they came with, and the the spray bar was a similar affair to what they use with the o-ring style needle valve and plastic back plate, which goes through the venturi like a normal spray bar. I don't know if it's the exact same thing or not, but I'm 99% sure it was not a spigot set up, but a 'blank" spray bar that installed like normal with a fuel line nipple, just no needle. It was smaller in diameter than a typical OS NVA spray bar. I had a Brodak .40 in a profile model I had flown quite a while, had a tank all sized out for that and was working nicely. I was going to get my son started on starting and flying bigger model with that airplane, and thought the rear needle valve would help him with the operation of the engine and keep his little fingers away from the prop as far as possible until he got used to them. I put the engine together with that original set up which consisted of a metal bracket that bolted over the back plate, the NVA which it turns out is the same NVA that OS used on a lot of their R/C carbs and is a very good unit, the spray bar and venturi. I took the model to SIG to fly it in their contest to shake it down, and discovered the tank wasn't big enough for the whole pattern using 10% fuel! It was quirky to start and didn't cut off cleanly but I figured all that stuff out. I finally took the spray bar out and measured it and it was quite a bit smaller in diameter, and this was because it didn't need to be threaded for a needle, I'm guessing, so this opened up the choke area a bit and used more fuel. I dropped down to 5% and the old stick in the venturi bit to get through the weekend until I found a smaller venturi or I put a bigger tank on it, I don't remember exactly. But the engine ran the same as it did with a "standard" NVA. It took a lot more choking to start it cold, and had to angle the back of the tank out and fiddled with tank location a bit to get a better cut off at the end of a tank. If you plug up the needle side of the spray bar with something and install in a normal .250 or there abouts venturi, it should run like normal. I found that a little dribble of solder on the tube for the exit of the NVA towards the engine helps the fuel line stay on. You can't add a big barb or anything because you have to be able to take the jam nut on and off. You can also drill and tap a proper sized venturi for the 4mm threads that the NVA has where it would thread into the old OS carbs, and install the whole NVA into the side as a spigot set up. You'll need to thread the case for some set screws to secure the venturi. I hope this all makes sense, but in short, yeah, you should be fine.
Type at you later,
Dan McEntee
Topic: Remote Needle Assembly Question. (Read 1973 times)
