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Engine basics => Engine set up tips => Topic started by: Steven Kientz on July 21, 2017, 04:36:04 PM
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I know that RSM and Aeroproducts have St style NVAs for Fox 35s. I was curious if anyone is using the Brodak25/40(4mm) NVA in a Fox 35?
I had to replace a broken needle valve(fox) with a packaged one(fox) in my box. Engine won't run after prime is used up. I figured spraybar and needlevalve not compatible, although they looked the same. I know that 4mm =.160 and its pretty big for the fox venturi. I measured the fox spraybar @.132
thanks
Steve
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I test that by filling a little cup with fuel. Hold the engine up over the cup with a fuel line running to the cup. Choke flip and see if the fuel easily travels up the line. If not, the spray bar fit is incorrect (assuming the engine is fine). I do this when building / tuning my speed engines. It's the last step, but important in my process.
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The engine will pull fuel when choke flipped. It will run long enough to burn prime. I have cleaned the filter, new glo plug and checked fuel line for leaks. I suppose I could pull NVA assembly from another Fox 35 and see if that works.
Steve
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Steve, I've been using the Brodak needle since they were first introduced. My dad turned down the center portion of the spraybar assembly to the same diameter as the stock Fox assembly. The problem is centering the hole, he made me some nice thick washers out of brass to do this. Shtterman on Ebay sells washers/spacers that would ultimately do the same. Very reliable runs using this needle. Typically the threads are tight on the Brodak in fact too tight. You sometimes have to carefully work the needle in and out with some oil and them clean it. I'm using two engines with this setup currently. Ken
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Thanks
Thats what I figured. Looks like buying replacements is the easiest(unless you own a lathe).
Steve
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Steve, you could chuck that into a drill press and carefully file and sand the throat area of the spraybar and come up with reasonable results assuming you have one. Ken
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Steve, you could chuck that into a drill press and carefully file and sand the throat area of the spraybar and come up with reasonable results assuming you have one. Ken
If you must, don't bother making it round, just shave down the sides and leave the top and bottom (where the hole is).
Brett
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I'm not going to potentially ruin a piece I can use on another engine as is. Dug thru some parts and found some ST35 NVAs and an OS 10NVA. If neither of those work the plane gets an OS25(LA,FP,F) or awaits the appropriate part from RSM.
Steve
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I setup the OS 20 or 15 NVA with soft metal spacer on both sides of the 20 and thin metal ones on the 15 size, they both work great, and are better than the Fox
I f you use a large diameter nva , then do not turn it down to size, most all of them will break
randy
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I have quite a few 1/2a, .35/.36 combat and stunt .35~.52 Fox/ OS/ ST/ K&B/ Enya engines where the venturi area and supplied NVA did not have the recommended open area
On Randy Smith's and Brett Buck's advice ---I DID NOT turn down the NVA diameter in a mill/lathe or drill press....each of their cautions was " too thin and liable to not tighten properly without stretching or breaking" so I followed the advise to file flats on both sides of the FAT ST NVA spray hole... to reduce / or perhaps...increase the flow volume
IMO this method works well ----BUT!!!
Ken Cook and I go back long way---- and he did NOT suggest hacking...he said...CAREFULLY ...RE RE-READ ---CAREFULLY sand and file the diameter down to increase the throat volume
I know if I had a good controllable method, I WOULD try his suggestion
I myself,, and I know Ken Cook uses, Permatex Anaerobic Gasket maker --- just about every where a model engine needs an air tight seal
carefully applied---with the Anaerobic Gasket maker, YOU DO NOT need 8~14 Inch pounds of torque to seat a NVA too be air tight, and not move, due to normal vibration
So there is a way ...or many ways.... to achieve the suggested --or recommended ----Venturi/ NVA volumes... proper venturi hole and several different NVA----spigot, sprinkler, remote, local through pipe, filter, panty hose, wood spacer, sleeved down adapter....there are a lot of variations that do work
And just to acknowledge a facts or two
When a 16 YO kid, I had no such internet resource ---and the hints in magazines of the time were deliberately false so I was lost and failed a lot....
Since 2012 when I came back to the hobby----I have followed the Fuel, Plug, Prop, NVA/Venturi...advice.... pretty much lock step with Brett Buck, Randy Smith ,Dirty Dan, Ken Cook, and Jeff Dawson for all my vast array of glow engines
Must be blessed....3 years of playing airplane now--- and no burps, run aways, flame outs, or too much tinkering with props and fuel mixes
I have bought NVAs and Venturies from Tower, Randy Smith, Lee Machine, Brodak, Texas Timers, and Doug Galbreth all after the good advice on This and other excellent forums
None of this was possible in 1971 no matter what magazine you read
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I know this sounds simple, but I have seen it on Fox 35's to many times. make sure you have the needle out far enough. On Fox needles it is about 6 full turns out to start.
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And Jim is the winner!! I left the OS.10 NVA in, but opened it 6 turns. It started, pretty rich, turned the needle in 1 1/2 turns. I had been trying to run it with the Fox NVA @ 3 turns.
Thanks again everyone for the help.
Steve