Hi Everybody:

         I was getting my OS .40S fired up in the Nobler and I was experiencing trouble getting a good setting.  Upon removing the spray bar, I noticed that it was a bit small in diameter for the .40.  Perhaps it would fit a .15-.19 engine.  When the new NVA was installed, I noticed that the hole in the spray bar was not in the centre of the venturi.  I tried about 4-5 other mfg. nva and they too would not centre.  Would this cause any problems with getting a good needle valve setting?  If so, what is a remedy?



                                                                                                                                                 Tia,

                                                                                                                                                 Frank McCune

Hi Frank

You just asked  about  2 problems  you lsted, the small diameter ??  are all of them too small in diameter?
The  NVA  not being  perfectly centered  will not cause that problem
The diameter being  too small  can cause that problem
what is the diameter of the  NVAs  you are trying  to use

Randy

Ever seen YouTube clips on two stroke engines with transparent heads and back plates?
Condensation seems to be prevalent no matter how its atomised at the front end.

     Hello All:

      Thanks for the prompt replies!

      Here are the diameters of spray bars that I have to use:

Enya .15-.19? .150"
Enya .29-.35   .155"
ST    .29-.35    .155"


     The recommended size is 3.9 mm or .154"

     The diameter of the venturi is about  No Go .2818", Go .2969"  These measurements areoapproximate as I only had a 9/32" and a 19/64" drills to measure the diamaeter of the venturi.  Perhaps this is too large for good performance.  I was told that the case was quite wide where the carb was installed on this series of engines.  I guess that I could get the hole in the middle of the venturi by turning a bit off of the shoulder of the spray bar.  I do not have a lathe anymore. Lol


      I should point out that the engine is in good nick and strarts neary everytime with one flick.  The engine is started in an inverted position!

      In any case, how can .005" make much difference in spray bar diameter make? I am thinking that I need a venturi with a throat diameter of about .270" or less.  It was suggested that a 7mm, .284", would be the correct size. ?

                                                                                                                                                   Tia,

                                                                                                                                                   Frank McCune


                                                                                                                                 













   

Randy, if the hole was significantly closer to one side, is it possible some of the spray could re-condense on the side of the venturi throat and dribble into the crankcase, fouling the f/a mixture... maybe too wet and flooding the crankcase?
Rusty

Most likey  NO, that would never happen, unless maybe... the  hole was almost, or touching the  side.
I would not think anything  he listed to be a problem  unless  the  hole  in the   case  of the engine is much larger than the spray bar diameter.
in that case  sealing the hole  very carefully

Randy

Frank,
To absorb the excess HP while getting useful pulling power at a reasonable lap time you could try a three blade Master Airscrew 10x5 (you may have to depitch from a 6). They are a good price for a test prop, can be heat pitched and look cool on a Nobler with a needle nose spinner.

What lap time did you get? For 68 mph on 60' lines you would be about 3.8 ish sec. and be over 11K rpm. At 8500 and a 7 pitch your lap time would be around 4.95 -5.1 depending on how much slip the prop has.

Best,   DennisT