Hello,

I saw Jerry's question here about NAVs for LA .40 and I have a related question but not quite the same.

I switched the remote NVA on my LA .40.  Used a ST NVA.  I had to drill out the case as the ST NVA is larger in diameter.  I noticed that the orifice in the ST doesn't  line up exactly in the center of the case.  It's off off a bit towards the fuel inlet side.

Does the hole not being centered have an adverse effect on performance?  I bench tested the engine after the conversion and everything seemed to be okay but I haven't tried it on a plane  as yet. 
                                                                                                                           
Does the NVA Randy offers require the LA case to be drilled out and will the orifice on Randy's end up in the center?

Thanks,

Joe

I used a drill press and vice to drill the case/venturi together.  That part turned out well.  I mainly wondered about the orifice in the spray bar not being exactly centered with the opening in the venturi.  Sounds like that's not a significant problem.

I wanted to try the engine in my modified Twister  this week end but the weather here (WV & Western PA) is really bad.  Winds up to 50 mph, blowing rain mixed with snow. 

Several well known fliers are at Brodak's this week end. Everyone hoped to have a little casual flying fun as well as testing some new stuff.  The trees were leaning at nearly 60 degrees from the wind.  Bob Zambelli was willing to fly but only with someone else's plane!  Just  kidding. . . No one tried it.

Thanks for the advice on the NVA.

Joe

Hi Joe,

If the hole is only slightly off center do not worry.  If it is a problem, can you put a fiber, or nylon washer, on the bar to line it up?  That works fine.  All you need is a good seal on each side of the case.

Bill <><

Hello Jim,

The problem with trying to center the hole in the venturi is the hole is off center in the venturi -towards- the inlet side of the spray bay.

In other words, the hole in the bar needs to extend further into the venturi in order for it to be centered.  I can't do that with washers or gaskets and there isn't any adjustment on the ST spray bar on the inlet side.  There's not enough metal on the engine case to counter bore it which would allow the spray bar hole to be centered.

As mentioned in other replies (Bill's) to my question, it's not that far off to matter much.  The engine seems to run pretty good so I don't think I'll worry about it.

Thanks for all of the advice.

Joe

Joe - for what it's worth,  I tried both the  OS and ST NVAs on various OS engines, including some LAs.

On my engines, the OS worked MUCH better and I did not have to ream the case.
I'm not a fan of the ST NVA - I prefer the positive "ratchet" type as in the OS and ENYA.

When you install it, have the hole in the spray bar turned slightly off center. The 4 to 5 o'clock position is where the pressure is lowest (suction is maximum). There was an interesting article regarding this in an older magazine.

Bob Z.

Hi, Steve - although I've never tried that, it seems like a good idea.
As we know, it takes a very small air leak to cause big problems.

I have seen that done on Fox .35 and some 4 stroke NVAs.

One thing I did notice - the threads on the OS NVAs are very precise - maybe enough that they won't leak air.

The SAITO uses a neat trick - they employ a tiny O-ring on the needle valve - a leak should be impossible.

Bob Z.