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Author Topic: Smaller Venturi for LA 25  (Read 1259 times)

Offline Allen Eshleman

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Smaller Venturi for LA 25
« on: May 05, 2021, 10:28:17 AM »
I have an LA 25.  Great runner but it must have one of the larger or largest venturis made for it.  It is drinking 3 oz. of fuel in just over 3 minutes.  It certainly runs fast and powerful.  What size of the smaller venturis, as in those made by Jim Lee would be a good one to try?   Thanks.

Offline Allen Eshleman

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Re: Smaller Venturi for LA 25
« Reply #1 on: May 05, 2021, 06:14:58 PM »
I just noticed the Post above with Randy Smith's recommendations.

Thanks Randy.

Offline Brett Buck

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Re: Smaller Venturi for LA 25
« Reply #2 on: May 05, 2021, 06:20:16 PM »
I have an LA 25.  Great runner but it must have one of the larger or largest venturis made for it.  It is drinking 3 oz. of fuel in just over 3 minutes.  It certainly runs fast and powerful.  What size of the smaller venturis, as in those made by Jim Lee would be a good one to try?   Thanks.

    Use the ****stock**** venturi and ****stock**** spraybar.  .257 and .135 respectively.

    Brett

Offline Allen Eshleman

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Re: Smaller Venturi for LA 25
« Reply #3 on: May 05, 2021, 06:56:33 PM »
Thanks Brett!

Offline Brett Buck

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Re: Smaller Venturi for LA 25
« Reply #4 on: May 05, 2021, 08:44:20 PM »
Thanks Brett!

  You're welcome.

     BTW, 3 ounces in 3 minutes is not way off for a brand new engine, with a richer-than-I-would-run-it setting or oversized prop. Over the first 20-30 flights, that will drop dramatically down to maybe 3.25 ounces for 6:25. You can tell it is very tight by noting how hot the front end/plain bearing section is getting. First run and it gets far too hot to touch. 10 flights later and its pretty normal.

     Brett

Offline RandySmith

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Re: Smaller Venturi for LA 25
« Reply #5 on: May 05, 2021, 09:31:53 PM »
I have an LA 25.  Great runner but it must have one of the larger or largest venturis made for it.  It is drinking 3 oz. of fuel in just over 3 minutes.  It certainly runs fast and powerful.  What size of the smaller venturis, as in those made by Jim Lee would be a good one to try?   Thanks.

OS makes a  296  , 281 , 255   nominal size, use the  255 if you use the  stock spraybar,  use the  281 if you use the  Standard  ST PA  Enya  size  .156 ,Then  they both will  act  just about identical to each other , just do not  mix them  or you will  get too small or  too large.

Randy

Offline Allen Eshleman

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Re: Smaller Venturi for LA 25
« Reply #6 on: May 06, 2021, 09:16:11 AM »
Thanks Randy.

That's the other piece of info I needed.  Have a great day!

Allen

Offline Allen Eshleman

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Re: Smaller Venturi for LA 25
« Reply #7 on: May 07, 2021, 07:30:04 AM »
Question about tongue mufflers.  Is it wise to drill more holes in the tongue mufflers Big Art and Jim Lee type?

Offline Dan McEntee

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Re: Smaller Venturi for LA 25
« Reply #8 on: May 07, 2021, 07:59:30 AM »
Question about tongue mufflers.  Is it wise to drill more holes in the tongue mufflers Big Art and Jim Lee type?

      Tongue mufflers can be pretty restrictive. I usually drill a whole extra row of holes to let the engine breath. If you can't exhale, you can't inhale either!! I prefer tube type mufflers because they allow the engine to exhaust better as long as the final opening is big enough, and if it isn't I make it bigger. The easier it is for the engine to exhaust, the better fuel draw it will have also. The sound doesn't seem to change much either. The muffler still muffles the sound and you can still tap it for muffler pressure. The best example I have seen of this lately is on another club members model with a Double Star .60 in it. It had an extra row of holes in the tongue muffler  and they were all plugged up with screws. This was a used model and engine so we were not that familiar with how the thing would run.  To trouble shoot an issue with something on it, it was suggested to remove all the screws and see how the engine responded. The model has a limited tank compartment and one of the things we were working on was getting a run time long enough for the pattern. He had already dropped down to 5% nitro, and removing all the screws freed things up to the extent of making the run time shorter, so he put about half of them back in, and this sent things back the other way and helped with the other issue, which I can't remember exactly what it was right now. Engines are pretty much all the same and basic things like intake dimensions and exhaust dimensions affect how the engine runs no matter if it's the hot rood sitting in your garage or the model airplane hanging on the wall in your garage. The exhaust and venturi size can affect each other and work for or against each other. Remember Eddy Murphy stuffing bananas in the tail pipe of his Beverly Hills Cop buddy's car??
   Type at you later,
    Dan McEntee
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Offline Brett Buck

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Re: Smaller Venturi for LA 25
« Reply #9 on: May 07, 2021, 10:21:08 AM »
Question about tongue mufflers.  Is it wise to drill more holes in the tongue mufflers Big Art and Jim Lee type?

     Maybe, maybe not. It depends on why you modified the engine (by replacing one of the rather important parts)  in the first place.

    Brett

Offline Dan McEntee

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Re: Smaller Venturi for LA 25
« Reply #10 on: May 07, 2021, 03:19:05 PM »
     Maybe, maybe not. It depends on why you modified the engine (by replacing one of the rather important parts)  in the first place.

    Brett

   On some models the stock muffler just does not work out well. On a Ringmaster, for instance, they are usually nose heavy without a muffler, and using the stock unit is just too much if you want a decent turn. Same with some other larger models and engines. I'm not a huge fan of the tongue muffler and prefer tube types because of the extra volume, but sometimes ya gotta do what ya gotta do!
  Type at you later,
  Dan McEntee
AMA 28784
EAA  1038824
AMA 480405 (American Motorcyclist Association)

Offline Allen Eshleman

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Re: Smaller Venturi for LA 25
« Reply #11 on: May 07, 2021, 06:23:31 PM »
My reason for replacing the muffler with a tongue muffler is to save weight.  On the other hand, I also thought that it would also run better although engine run is not my problem.

Offline Dan McEntee

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Re: Smaller Venturi for LA 25
« Reply #12 on: May 07, 2021, 09:52:44 PM »
   

     https://stunthanger.com/smf/engine-set-up-tips/venturi-inside-diameters/

    Check out this thread that is pinned to the top of the section. It has some relevant information to the subject and since it's pinned to the top of the list it will be easy to find for future reference.
  Type at you later,

  Dan McEntee
AMA 28784
EAA  1038824
AMA 480405 (American Motorcyclist Association)

Offline Brett Buck

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Re: Smaller Venturi for LA 25
« Reply #13 on: May 08, 2021, 02:45:51 PM »
My reason for replacing the muffler with a tongue muffler is to save weight.  On the other hand, I also thought that it would also run better although engine run is not my problem.

   It will not run better without the muffler. It might run faster is some conditions, but not in any way useful for stunt. The other advantage is that if you run the stock parts, I and many others can tell you *exactly* what it is supposed to do and know that the basic engine is going to work. Any other issues are setup problems.

     Brett


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