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Engine basics => Engine set up tips => Topic started by: David_Ruff on December 14, 2023, 02:09:49 PM
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I need the washer size for a Fox 35 using a ST style NVA.
Thanks in advance.
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I am thinking 5/32 ID. I measured the NVA at 0.155 in. 5/32 is 0.156?
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McMaster-Carr sells washers with these spec's. They work great for centering ST style spray bars.
P/N 98032A436 Cad. plated steel ID .156" OD .250" Thick .013"-.020" $3.72 per 100
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Where is this washer supposed to go?
Yes, 5/32 is 0.156 inch (4mm). The ST spraybar is of larger diameter than the Fox factory unit. I do not remember the diameter of the Fox spraybar. I am thinking it is about 0.125 inch. If you use the ST unit, it will result in a reduction of air getting into the engine. Thus, you have to reduce fuel flow accordingly. The Fox needs plenty of oil, which means reducing the fuel flow is not doing the engine any good.
When I used the ST needle, I had to neck down the spraybar to get the airflow back to what it should be. The Fox venturi is cast as part of the case so I did not want to change that. The engine would overheat and "run away" into a constant 2-stroke part way thru the pattern with the 4mm ST spraybar.
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https://brodak.com/6-5-32-i-d-flat-washers.html
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I never had that problem. They always seemed to needle better with the higher quality ST NVA. I will admit that I've had problems with some of the RSM clone NVA's. The problem has always been with the needle itself, and is cured with a true ST needle or one of the Enya ST needles from shtterman. FWIW, I have always run Fox 35's on 10% 11-11 fuel.
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The ST needle is certainly an improvement over the Fox unit. I had the runaway problem on engines with the Fox factory ABC kit. Maybe that is why I had the runaway problem. I like that ABC kit. Lighter piston, less vibration, and no need to run 28% all castor.
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If you have an Ace hardware near you, they sometimes have small fasteners (loose) in bins/drawers.
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Dave,
One of the problems that can sneak into the Fox35 NVA setup is air leaks around the case mount for the spraybar. I had a problem with a Fox that would start and set into a great 4-2-4 until the vertical 8 then start to lean out and go over. I tried all the usual suspects, plugs, fuel, tank leaks, etc. None worked, then by chance (better to be luck than good any day) I was there was light around the edge of the spraybar boss, I sealed this with high temp silicon sealer and boom problem solved. As the engine case got warm the air leak got bigger and leaned out the mixture. So seal both sides of the NVA mount.
Best, DennisT
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Hi Dave:
I have been using a number 6 plastic washer found at the large building supply store’s hardware section. You may want to alter the i.d. to suit and seal the joint, but they work!
Stay well,
Frank McCune