News:



  • June 15, 2024, 10:51:28 AM

Login with username, password and session length

Author Topic: Venturi size?  (Read 940 times)

Offline Joe Messinger

  • Trade Count: (0)
  • Commander
  • ****
  • Posts: 331
Venturi size?
« on: February 05, 2007, 01:32:40 AM »
Hello,

I have changed the NVA on my OS .40 LAS from the remote set up to a S.T. NVA.  The S.T. spray bar is .020 bigger in diameter than the stock OS bar.  The OS venturi has an I.D. of .283.  Should I enlarge the venturi to .303 to make up the difference of the larger S.T. spray bar?

Some recommend an opening of .260 for a .40 venturi.  Maybe the added reduction with the S.T. bar would be a benefit?

Any advice appreciated.

Thanks,

Joe
Joe Messinger

Offline Manuel Cortes

  • Trade Count: (0)
  • Commander
  • ****
  • Posts: 276
Re: Venturi size?
« Reply #1 on: February 05, 2007, 03:14:21 AM »
Hello, Joe.
Before tinkering with venturi size, IŽll give it a try with the new setup.
Just for the record, my ST 46 runs almost same power with .174 and .190 id (sprinkler type) but a lot sweeter with the first, and easier on fuel.
Give it a try, probably it will be OK.
Then, if it lacks power, begin raising the effective area drilling the insert.
Hope it helps.
Manuel.

Offline Ward Van Duzer

  • 2015
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1284
Re: Venturi size?
« Reply #2 on: February 05, 2007, 09:14:19 AM »
Another way of handling the ST needle valve thingie is the relive the spray bar some as shown. No, not as precise, but very helpful for opening up Foxes and other early venturis.

Ward
I hate spelling errors, you mess up 2 letters and you are urined!

Don't hesitate to ask dumb questions.
They are easier to handle than dumb mistakes!  Ward-O AMA 6022

Offline Joe Messinger

  • Trade Count: (0)
  • Commander
  • ****
  • Posts: 331
Re: Venturi size?
« Reply #3 on: February 05, 2007, 03:17:07 PM »
Hello,

Manuel:  I'll take your advice and try the LA .40 as is with the ST NVA.  That is , I'll try it when (?) the Artcit weather we've been having lately here in WV decides to  give up.  Minus 2* this morning and the high for the day was only 9*. 

If the engine needs more venturi area, I can open it up later.

Ward: Great idea! I wouldn't have thought of doing that.  Might be better than boring out the venturi.

Thanks to both of you.

Joe
Joe Messinger

Offline Jim Thomerson

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 2087
Re: Venturi size?
« Reply #4 on: February 05, 2007, 06:54:47 PM »
A comment on Ward's relieved spraybar.  I think he means to take a file to the sides of the spraybar, rather than turning it down.  If you turn the spraybar down you weaken it unnecessarily and you can break it if you get ham-handed tightening it down.  Been there, done that.

Good advice to fly and try.  Side comment, I have seen a side mounted LA 25 run great with the remote needle. 

Offline Steve Helmick

  • AMA Member and supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 9956
Re: Venturi size?
« Reply #5 on: February 05, 2007, 07:58:43 PM »
IF you bore the venturi too big, you can make it (effectively) smaller by adding a Bruline air filter (Tower has 'em). The green (fine) is supposed to be equal to .020" reduction, the black (course), .010". An air filter is a very good thing for your engine, and helps starting. Put a few drops of fuel on the filter and you got fumes going into your engine...perfect. Especially helps inverted, IMO. If you happen to know where you can get some gnarly old used panty hose or nylons, you can put several layers on with an o-ring, safety wire, etc., for the same effect, but cheaper and more compact.  y1 Steve

PS: I've also seen OS engines run terrible with the rear needle valve. Probably more to do with the crumby plastic backplate, though. A good one has to get through QC once in awhile!
"The United States has become a place where professional athletes and entertainers are mistaken for people of importance." - Robert Heinlein

In 1944 18-20 year old's stormed beaches, and parachuted behind enemy lines to almost certain death.  In 2015 18-20 year old's need safe zones so people don't hurt their feelings.

Offline Joe Messinger

  • Trade Count: (0)
  • Commander
  • ****
  • Posts: 331
Re: Venturi size?
« Reply #6 on: February 05, 2007, 09:47:07 PM »
The biggest problem I've had with the remote NVA set up is, for whatever reason, the engine speeds up and slows down repeatedly at the end of the flight.  Sometimes 12- 15 laps before it finally quits.  Very annoying! The earlier part of the run is fine.

Using the same fuel system, and no changes other than a through the venturi NVA, the problem goes away.

I'm sure others haven't had any trouble with the remote set up.  I just have to go with what has worked for me.

Joe
Joe Messinger


Advertise Here
Tags:
 


Advertise Here