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Engine basics => Engine set up tips => Topic started by: Bootlegger on November 08, 2013, 04:22:34 AM
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Yesterday I put a double hole spray bar in an OS LA 46, I soldered one hole shut before installing it, the holes were smaller than the hole in the original spray bar, should I drill the hole out to match the original, or try it this way??
What say you, and why?? Thanks a lot...
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Gil, this begs the question: why did you solder one of them shut?
As for needing to open the remaining hole: I suggest you run the engine with it in its original size and see how it sounds, then make a decision on whether the needle responds as you would like, whether the engine seems to have the power you expect.
Bill
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It also begs the question who's spraybar was it? The two hole arrangement that is most know is the old Fox 35 NVA. The holes are drilled just slightly off centerline and are meant to be positioned with the holes across the venturi just out of sight (if you can see both holes you need to rotate it 180 degrees to get them in the proper location for max draw). This should give very good fuel draw if the needle is sealed both against the venturi body and where the needle enters the spraybar which was a weakness of the Fox NVA (some guys use silicon sealer against the body and a piece of fuel tubing on the needle threads which sometimes works).
By soldering over one hole you may not get enough fuel flow to get a good stunt run if you run open uniflow. If you run crankcase pressure then almost anything will work but the needle may be sensitive to set. Muffler pressure is in the middle and you need to just try it.
I personally like the Randy Smith NVA's or the RMS ST NVA's. Remember to check the "open area" for the specific diameter spraybar you install, the ST style is 0.150" and the OS stock is around 0.135", get the venturi sized correctly.
Best, DennisT