Brodak 25 venturi size?

[frank williams]

I got my Brodak 25 running the best it ever has by switching to all synthetic fuel.  The venturi that is in it is a 0.247 dia. with the .157 dia. spraybar.  Is this venturi bore too small?  Good draw, but power seemed down.
Frank

[Wayne J. Buran]

The Brodak 25 I had seemed to be the happiest on a 10% blend. Props varied on application and I always ran a uniflow tank.
Wayne

[Brett Buck]

I got my Brodak 25 running the best it ever has by switching to all synthetic fuel.  The venturi that is in it is a 0.247 dia. with the .157 dia. spraybar.  Is this venturi bore too small?  Good draw, but power seemed down.
Frank

  No one seems to believe me when I talk about oil drag, or about viscosity of the fuel affecting the flow stability.  All I can say is that I think you want as thin an oil as you can safely get away with, and as little flow restriction in the fuel supply you can possibly get.

    Brett

[bob whitney]

from what i can tell ,the B25 has almost no taper in the sleeve so piston drag with a lot of caster could be a problem ,along with a tight bushing up front .Blendzall makes a thin g Go Cart caster oil -ULTRA racing caster that works very good

[john e. holliday]

Thanks guys for the info.  I just mounted up a brand new B-25 on a Sky Ray that was collecting dust.   Took me a while to get all the crud off the plane.

[frank williams]

Stock venturi? or something larger?
Frank

[Mike Greb]

Might try boring it out about .01 inch and see if that makes any difference.   The one that I ran in OTS seemed rather weeny.  I am running that same engine in super slow rat with a .316 venturi.   I have run it thousands of laps in the super slow rat and it just keeps on going.  It was down on power at this years nats.   I devarnished the piston and liner, and now it is back to were it was.

[BillLee]

Stock venturi? or something larger?
Frank

Frank, for your SSR, you'll want to put about a .320" venture with a full spray bar.

You ARE talking about SSR, aren't you? 

Bill

[Balsa Butcher]

Hi Frank, I have run the B-25 in both stunt/sport and SSR applications. Found it to be lacking in power with the stock venturi as you did. Put in a venturi from a B-40 which is about .305. This woke it up and is what I would do to start with. For SSR (as has been posted) even larger venturis can be used. I run a 9x4 prop for sport/stunt, an 8x6 for SSR. The other Lee (Jim) sells venturis of various sizes for this engine. I'm using one his on my B-40 (.283). As far as fuel goes, I'm happy with 10/22 GMA but may try full synthetic and see how it works.  

[Dane Martin]

i haven't seen a lot, but the ones I've seen running very well were on a .255 venturi.
i agree with Brett on the fuel. you might look into the Brodak 10/11/11. but being a newer style engine, it might only "want" 18% oil.
I'd call John Brodak and ask him the oil content preference.

[Motorman]

I don't have the numbers right now but, my B25 was much happier after I opened up the venturi.

MM

[frank williams]

Thanks All
I think I'll open it up a bit ....... its for a smalish (375in**2) stunt ship, not SSR, ... although you never know.
The fuel I ran was 15% w/23%low viscosity oil from VP.  Its one of their standard heli fuels, not bad for PA's either.
Frank

[Bootlegger]

 Did running it on all synthetic have any adverse effects on the longevity of the engine? I am curious about only syn fuel in the newer engines, and am willing  sacrifice an engine to the cause, but I am still interested/concerned about the engine with only syn fuel also...

 Thanks

[john e. holliday]

Only experience I have is that you do not want to run the engine over lean too many times.   But, some of my engines run better with no castor.   Now the old Fox's are a different story.