Oh boy... I can't wait to see all the replies to this one...

The 35 and 40FP have had so many followers, and as many different methods of dealing with the problems, that a person could spend the rest of their life fiddling and never get anywhere.

You could use the stock venturi (the 35FP uses the same size venturi as the smaller one that is shipped with the 40FP), and run the stock muffler, and a 10-6 prop.  Set to a 4-2-4 break.  After awhile it'll probably take off on a runaway to the tune of 4 second laps and a brite red palm. 

After that we tried the 20-25FP venturi, which drops in without any mods.  With everything the same it worked pretty good, but still would run away from time to time... 4-2-4 until the runaway...

At some point we started using the Rev-Up 11-4 and 70ft eyelet to eyelet lines to slow down the plane... That didn't last too long, but it worked well while it lasted.

Then we switched to the high rpm low pitch method...  Different props, different fuels, different mufflers, head gaskets, tanks, blah blah blah... Still ran away.

I've actually got about 4 of the 40's and 5 35's now, and I never run them anymore.   I've phased them out replacing them with Fox 35's, Tigre 46's, and Max-S 35's.  My opinion is that the 35 and 40FP have too much power for the size planes they're typically used on... Something larger, like a Magnum might be enough plane to load it down a bit, but why build a plane like that for an FP when there are Tigre 51's?  There are better engines out there, that cause less frustration.  Finding time and a place to fly is already hard enough, no sense in wasting the occasion fighting with an engine that requires constant tuning.  Even when they did run right for months, they'd run away at a contest and blow over the time limit costing pattern points.   Short tank it and it dies in the overheads. 

Sell it to a collector, or a diehard FP lover... One of my better 35's is on a carrier plane, and does that job ok.

Well guys, I'm from the other camp. Please send your unwanted FPs here. My Twister runs very well with an extra head gasket, free flowing exhaust- tongue muffler with a lot of holes, a large .283 ventuuri, a 101/2x41/2 apc, powermaster %5, %22 (50/50). Jack Weston runs his FP40 in a Gieseke Nobler with the same set up. As do many of our club members. We have about ten stunt planes in our club running this way. Including an overweight fuel soaked Oriental. Both old style and new style (ABN) FPs work for us. Jack's plane is often complimented for it's run and great break. Even my ugly Twister gets its perks. Engine has that much controllable power.

The key to these engines is to run a lot of fuel through them in order to cool them off and keep them from running away. In this mode they generate lots of power and are controllable breaking from a wet 2cyle to leaner 2cycle. Large venturi, free flow exhaust etc. OS sent the stunt version of FPs out configured the way I described above. Perhaps part of the problem is our use of RC FPs that need this simple configuration.

In my experience small venturis sometimes work in light sport planes. I run .265 Venturi in the FP in my Galaxy. But with my Twister, that's a definite no no. The Twister was built somewhat heavy. Five ply in the nose. Half-ribs, webbing between the wing spars and at the trailing edge. It was a kit plane to boot. Had it out today. Flew quite well as it did last season. The steel cylinder old style FP pulled like a bear. Five second laps or so on sixty foot lines. Lots of tension, plenty of time to do the maneuvers. Even as the weird winds blew.

Many times an ill matched prop, wrong fuel, a constricted exhaust and the smaller venturis cause the typical FP problems. Don't believe we've ever had an FP that we could not tame using the simple mods described above.

Man, feels like I do this post every week.

Seems to me ST46s were around simultaneously with FP40s. Also, plenty of OS35s' must have still been available.

Jack scores real well in advanced with his FPs. Mike Palko ran an FP before he went electric. Dan Banjock took Jack Weston's Twister (FP powered) and won profile two years ago at Brodak. Then there are the standard Foxes the Philly Flyers run. Ones that are broken in and left alone. Lots of those have won stuff in OT. Lets see yesterday I saw four or five FPs run well at our field and three or four standard foxes. Stunt planes and sport planes. One guy had an erratic run with a fox. Small hole in tubing. New tubing, ran well.

Opening the exhaust or using a free flowing exhaust is usually necessary in an FP. The right fuel, right prop etc. An extra head gasket or two. A large venturi is often essential in anything like a full sized stunt ship. Of course many who think the engine isn't worth squat keep recommending a small venturi. I pulled a standard venturi out of a brand spanking new LA40 the other day, just to see what OS does. Large FP venturi .283.

There are also issues about rigid front ends in profiles.

Every now and then one of our FPs gets a head hemied. Further lowers compression, I guess. That's the most we do. Perhaps a third head gasket would have the same result. A member scored a brand new in the box FPS at the last Lebanon Super Swap. Low and behold it came from OS with an assortment of head shims and venturis.

If you had an overrun coincident with your runaway, I suspect your FP was subject to the standard problem of too small a venturi and an overly restrictive exhaust. Fuel must pass through the engine to cool it off. Low fuel consumption is usually a bad sign. Open up the exhaust, put in .283 venturi.

Dan had similar problems with FPs for a long time, until Bill Suarez told him to put in a big venturi and open up the exhaust. The 50ounce fuel soaked Oriental ran great after that. Engine is still pulling that clownish effective combo. Despite shaft runs and numerous crash burials in our field of dreams. It's gone through three or four owners (renters?) since Dan was enlightened many many years ago.

Foxes at times have issues with overly tight piston/cylinder fit. Ahh Foxes, another debate.

Best,

Dennis

Hi Andrew,
All the FP's are R/C engines, the S version just has a venturi and needle valve.

Mike Clark

Well Fellas, something else occurred to me as I was thinking the FP issue over. Let's not forget the tuner. The one in a group who's stuff, whatever the engine, runs well. Do you know the guy? Perhaps many of us are not so lucky to have a talent like that at our elbow. In the Philly Flyers Dan Banjock usually leads the rest of us dumbells onto the right path. A few others are gifted but not as much as he. Dan can usually size up an engine problem and come up with something simple that works. Quick fast and in a hurry. He's the guy who says open up the exhaust, change the venturi, use this plug and that fuel and so and so prop. A mix of experience, sensitivity and empirical research. He's gone down lots of wrong roads. When you listen to him, saves a lot of time and avoids frustration. I'm sure that's part of the reason many of us in Philly run engines without internal mods.

Even the expensive stuff (sometimes especially the expensive stuff) needs to be dialed in. Set up with the right head clearance, fuel, prop, tanks, break-in regimen. In my experience, many times poorly running engines have not been set up well. Not an issue requiring redesign. The design can serve as is, it's more a matter of discovering the combo of fuel, prop, venturi, tank etc. that works.

I read all the replies... But it doesn't change the fact that I've been there, done that, and I've moved on.  If you think 35 & 40FP's are great, then so be it.  But please don't try to convince me I'm wrong.  I don't want to get into a debate about it, or talk about all the things that can be attempted to make them run right... In my experience they don't, and I'm not going to try any more fixes. 

Thanks! But no thanks.  That's my opinion, take it or leave it.

Hi Bob,
Just saw your post. We use FP needlevalves, which I guess means more net venturi area. Also muffler pressure to a non uniflow vent.

Best,

Dennis

One extra head gasket (or two if needed), powermaster 5%,22% (50/50) I've been running that in my iron sleeve FPs as well as the ABN FP and ABC Tower. 101/2x41/2 apc. Open up the standard exhaust or use a free flowing tongue. The earlier muffler which uses a center exit, sometimes needs the tip removed, and exit hole opened to the diameter of the lopped off stinger. Enya #3 plug, which is a hot plug, also helps to cool the combo out. Big venturi. Set it in a 2cycle. Should sound fat and happy and somewhat loud. If engine runs away and fuel consumption is low. Open up the exhaust more and perhaps venturi will also need opening to compensate for the thickness of the ST needlevalve. Best of luck. Tell us how it goes.

You know, it's funny, but my favorite all time profile engine is my ancient Byron Barker OS 40FP.  Has the sweetest 4-2 break with a ton of power.

Bill <><

....10 1/2 X 4 1/2 APC is magical....

Rich,

That 10 1/2 X 4 1/2 APC seems to be magic on a whole lot of engines, but don't tell nobdy! 

Gotta keep SOME secrets!      

Bill <><