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Engine basics => Engine set up tips => Topic started by: Robin_Holden on August 27, 2009, 01:12:49 AM
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Advice please fellas.
Just converted one of my engines , an OS 46LA to C/L.
The only NVA/Spray Bar assembies I have place the hole in the venturi slightly off centre.
So , does this make any significant difference please ? If it does , which NVA do you recommend please ?
Much obliged ,
Robin.
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Robin, if the offset in only about 1–1.5mm, there shouldn't be a problem.
The OS part number for the factory NVA is 22311000, Tower part no LXCR49m, price US$13.49.
Cheers, Geoff
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Geoff , very much obliged for the info.
Many thanks from S.W.France ,
Robin.
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Hi Robin
Geoff is right ,it will make little to no difference if it is off a little, and then only on a profile would you see any difference at all
Randy
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If your engine is upright or inverted, it will make no difference. Side mounted, it does make a difference. Move the tank up or down a little as needs be. I have swapped out NVA's on a profile when the tank was hard to move.
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Hi Robin
I didn't think about the issue of profile models—thanks gents for pointing that out.
Another thought though. If your spray bar is a little long, a washer under the hex of the spray bar could get it back on centre. I have used nylon washers from an electronics store to centre the hole exactly and prevent air leaks.
Cheers, Geoff
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I've used nylon washers, but don't any more. They over time give a little and loosen up, leads to the NVA rotating and air leaks. I now use alum spacers when I need to center a NVA. I put a little silicone goo on if worried about leaks. For ST type (4mm dia) I use K&S heavy wall 1/4" alum tubing, ream it out to 5/32 then part off to the right thickness in a mini lathe.
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I was having the same touble centering the spray bar hole in a couple of engines and remembered this thread. I started digging through some of my old (real old) parts and pieces and found two NOS Perfect NVA assemblies with needles. These were interesting as they were set up with adjustable nuts on each side and coud be adjusted to fit the engine. The hole looked a little small to me but I am going to try one out and see. Does anyone offer an NVA like that today ???????
Dalton H.
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Dalton,
The old Perfect brand after-market spraybar+needle setup is also usually smaller diameter than most modern NVAs. That may - no, will - make a difference in needling and general usefulness. Muffler pressure may reduce the effect and allow a bit more power from a less-restricted intake. ASIR, most threads and needle ratchets were fairly coarse, and threads a bit loose in clearances... Tendency to leak air?
Dead-centering the spraybar jet is not essential - close to centered seems plenty good. And you can punch holes in thin aluminum, such as the tops of pull-tab cans, with a pliers-type squeeze punch for, like, 1/4" holes. Those punches come in several diameters, often found at craft sections in big box stores. E.g., I use 5/16, 1/4, 3/16 and 1/8 punches. For spraybar diameters, I usually drill the appropriate diameter first, then center the drilled hole by eye in the appropriate hand punch. ...Let's you work in a fineness of a few thousandths of an inch, and with metal that doesn't keep crushing down like nylon or other plastic or gasket stock.
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Thanks for all the info Lou, the dia. does look small. Unfortunate as a setup along this idea using up to date materials might be a nice thing to be able to buy.
Dalton