McFrank,

I don't even know where to begin.

We use these to race Super Slow Rat. Don't really need to quote you a bunch of rpms or anything. Here's the deal:  on 60' lines, using a 9x6 prop, for a good engine that is not damaged or modified in any way, it will really move out. Waaaaay better than an OS 25 LA. Shouldn't have any trouble dragging around a Super Clown or a Sterling if they are less than 10 lbs and somewhat straight. If your engine won't screw you into the ground on 55' lines then it was either a factory dud, or some unscrupulous motor molester has put his hands on it.

Suggestions/questions:
1. Did you get the engine new, or did someone have their hands on it? If so, what did they do to it? If it is beyond lame and likes to run backwards, check the liner to be sure it is not in backwards. (If you are flying it, I doubt this is your problem.) If you turned the needle in and it won't scream with a 9x4, then I would pull the head and see if someone accidentally lost a whole bag of head shims in there. It's happened.
2. Is it broken in? Some of these were set up pretty tight, and until they get some time on them they don't develop full power.
3. Did you really run it in a 2-stroke setting, or are you trying to make it run like a Fox? If you want to 4-stroke it, then I can't speak to that approach knowledgeably.
4. What size is the venturi? These engines can make much more power if you open it up, and they still draw fine. Again, in 2-stroke mode. If someone tried to turn it into a Fox, they might have tried a tiny venturi, too. I'd have to go look at the arrangement again, but if you stuffed an ST needle in a smaller hole, then it is going to be gutless.
5. Did you try a 9x5 or 9x6? You say the airspeed is too slow but you also say it runs nice. Try props!

There may have been different factory venturi sizes. And there have been reports of "slower" 25's. I saw a couple myself on racers. They were just a tad off, not some huge amount like you describe.

One other thing I should mention. I found one Brodak 25 that a friend had on a Goldberg Shoestring. It ran slow and unsteady. It felt fine cold, but hot restarts were a problem. When I looked at it, I found the fit was bad. I took off the muffler to look at the piston. The problem went away immediately. The problem was that the face of the muffler was not machined, and when bolted to the engine warped the case and liner. So we lapped the muffler and proceeded to put up perfectly good runs.


Divot McSlow

      Hi Dave:

      Thanks for the prompt and informative reply.  You have prompted me to take a closer look at the B 25.  A flying mate flys an OS .25 LA or FP on a Magician and that engine pulls that plane very quickly!

      I always ran this engine in a wet 2 cycle where it had room to gain some rpm in the maneuvers.  Never too lean!

      I will get back to you after I examine the engine more closely.

                                                                               Be well

                                                                               Frank

I think the Brodak 25 and 40 both use a factory spraybar of 0.156 inch.  The ST spraybar you have in the Brodak 25 is probably 0.156 diameter as well.  So, no difference there.  But, a venturi of 0.250 might be a bit small.  I think it needs to be 0.255 - 0.260.

You might find such a size from one of the vendors listed on this forum.

Try a 9 X 5 prop.  A pitch of 4 might not be enough to get the airspeed you need.

I had the same experience with the B-25. Cured it by substituting the stock (way too small) venturi with one from a B-40, about .305 or so.
Really woke it up. It is now on a Super Slow Rat, no muffler, swinging an APC  7 x 7 prop really, really, fast. Bottom line is; try a larger venturi, it may be the only change you will need.  The 7 X 7 prop is just for racing though, I'd retry the 9 X 4 for stunt. 

         Hello All:

         PROBLEM SOLVED

         The venturi was opened up with a 17/64" drill and now the engine runs very well.  I used a 9-6 wooden prop, 10-11-11- fuel and it became a beast!  Great power and speed made flying the Sterling F 51 a joy.

                                                                                                                                                                          Let the good times roll

                                                                                                                                                                          Frank McCune

Brett,

Please excuse my ignorance here, but what is the "88" you mention?

Bill