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[Motorman]

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[Brett Buck]

I've never stunted this engine just raced it on profile planes. I got a nice break into a 2 stroke on wingovers and inside loops so I made a stunt tank. dang if this thing didn't flame out on almost all outside loops. Raised the tank all the way up but no help. I leaned it down but it was too fast. Profile racing plane is too heavy with no flaps anyway so I'm wondering if it's worth it to build a new plane. I like upright engines but do you get a better run with upright or inverted cylinder. Will the cylinder orientation eliminate the flame out?

   Inverted or upright will likely cure the "burp", but the bypass stuffer mod definitely cures it for profiles and doesn't hurt anything else. Takes about 10 minutes if you have a bit of spruce or basswood handy. 

    Brett

[ChrisSarnowski]

I would take Brett's advice, but I wonder what glow plug and prop you are using?

You could try a plug with an idle bar so that the plug has a better chance of staying lit.

-Chris

[ChrisSarnowski]

Looking at the MECOA site, I think the K&B R/C long with idle bar #4520 might work better.
That is similar to a SIG R/C Long, Thunderbolt R/C long.

Perhaps you might like a 10x6 or 10x5 APC prop on the Fox 35.

-Chris

ps. Fox should still sell the stuffer backplate.

[Brett Buck]

A K&B 1L and a MAS 9-6.  Does anyone still sell that stuffer backplate?

   Yes. That will not likely help this issue. The solution is the bypass stuffer a la Frank Williams:

http://stunthanger.com/smf/index.php?topic=3878.0

    This directly corrects the root cause, instead of tweaking around the edges of the problem.

     Brett

[Dennis Moritz]

Lots of Philly Flyers get the stock Fox to stunt.

[john e. holliday]

I have run the old reliable Fox .35 Stunt in about any configuration you can think of.  Never had a problem with them cutting out unless there was a problem with the fuel delivery.   My son and I was breaking one in on the plane by flying it rich.  Would cut out after about six laps.   Seems we had a spit fuel line.   Another time it was a bad fuel tank.   Have you tried changing tanks?

[Brett Buck]

I have run the old reliable Fox .35 Stunt in about any configuration you can think of.  Never had a problem with them cutting out unless there was a problem with the fuel delivery.   My son and I was breaking one in on the plane by flying it rich.  Would cut out after about six laps.   Seems we had a spit fuel line.   Another time it was a bad fuel tank.   Have you tried changing tanks?

   For goodness sake, the bypass stuffer modification IS THE SOLUTION to this issue. There may be other problems but the stuffer mod is the answer for the burp. He has already had the absolutely classic case of it.

     Brett

[George]

   For goodness sake, the bypass stuffer modification IS THE SOLUTION to this issue. There may be other problems but the stuffer mod is the answer for the burp. He has already had the absolutely classic case of it.

     Brett

You can lead a horse to water...

George

[ChrisSarnowski]

There is nothing else like a good Fox 35 burp discussion.

Try the bypass fix.

-Chris

[Perry Rose]

If you got a good run with the first tank, go back to it.

[Randy Cuberly]

Good Grief...just when you think everyone in the WORLD knowa about the Fox Burp in profile configuration, this conversation comes up again.

Believe me the Fox Burp is REAL...some engines do it drastically and simply quit as yours did.  Some just stutter and >>>BURP<<<but continue to run.  A very few "burp" but do it gracefully and don't really create a major problem...but they all do it...
I've heard Burps that the pilot said didn't exist...Who knows!!!!

Trust me...Do what Brett says and follow Franks cure...They're both very smart guys and nice too...just do it.

Don't listen to the peanut gallery!!!

Randy Cuberly

[ChrisSarnowski]

Greetings from the Peanut Gallery!

[BillP]

Up or down? It didn't make a difference for me in the upright position. I tried 3 different 35 stunts in an All American SR...two hemis and one stock. All burped same as the many profiles I've flown them in. The only way I've found to avoid the burp on a stock engine is to do very large outsides. Seems to me the fix is as stated already with the wood plug.

bp

[John Craig]

I have run the old reliable Fox .35 Stunt in about any configuration you can think of.  Never had a problem with them cutting out unless there was a problem with the fuel delivery.   My son and I was breaking one in on the plane by flying it rich.  Would cut out after about six laps.   Seems we had a spit fuel line.   Another time it was a bad fuel tank.   Have you tried changing tanks?

I believe Doc H. has the answer.  Look for a fuel feed problem first.
I had the same problem this  Friday.  Fox 29 on a RM flaming out at the top of an out side loop. I have gone with the fuel delivery system as the problem & moved my tank up 1/8 inch & will try again next weekend.  Why??  1. It seemed a tad rich inverted.  2. This will place the tank at the same level as the tank/Fox 35 on my FliteStreak.  I miss measured when I mounted the tank after a major re-build on the RM. The FS runs great!!  I could not ask for any better! 3.The other reason, I already have a stuffer in both Foxes.  

Fastest way to check, if it is tank position.  When lap time inverted/upright are equal or inverted/upright RPM are equal.  Then the tank is in the right position.  

[Randy Cuberly]

I believe Doc H. has the answer.  Look for a fuel feed problem first.
I had the same problem this  Friday.  Fox 29 on a RM flaming out at the top of an out side loop. I have gone with the fuel delivery system as the problem & moved my tank up 1/8 inch & will try again next weekend.  Why??  1. It seemed a tad rich inverted.  2. This will place the tank at the same level as the tank/Fox 35 on my FliteStreak.  I miss measured when I mounted the tank after a major re-build on the RM. The FS runs great!!  I could not ask for any better! 3.The other reason, I already have a stuffer in both Foxes.  

Fastest way to check, if it is tank position.  When lap time inverted/upright are equal or inverted/upright RPM are equal.  Then the tank is in the right position.  

People keep talking about a "stuffer"...if you're talking about a "stuffer backplate as one gentleman earlier mentioned, that has nothing to do with the "Burp Problem"  The Burp is created basically by a too large and poorly positioned bypass port in the cylinder.  The "stuffing that needs to be done is placing a wooden stick of a given size in the middle of the bypass port to reduce it's size...it works very well and fixes the problem. 
Nothing else discussed here will fix the burp, especially on an engine that has a burp drastic enough to make it quit.
This is Gospel...use the link Brett provided and follow the instructions...anyone that can use a screwdriver and an xacto knife (or even a pocket knife can) easily perform the mod. 
All of the other discussions are just window dressing.

Randy Cuberly

[Phil Bare]

I've never stunted this engine just raced it on profile planes. I got a nice break into a 2 stroke on wingovers and inside loops so I made a stunt tank. dang if this thing didn't flame out on almost all outside loops. Raised the tank all the way up but no help. I leaned it down but it was too fast. Profile racing plane is too heavy with no flaps anyway so I'm wondering if it's worth it to build a new plane. I like upright engines but do you get a better run with upright or inverted cylinder. Will the cylinder orientation eliminate the flame out?

MM

Put an 11x4 on it and lean it out. I have done it for years. You will like it.

Phil

[ChrisSarnowski]

People keep talking about a "stuffer"...if you're talking about a "stuffer backplate as one gentleman earlier mentioned, that has nothing to do with the "Burp Problem"  The Burp is created basically by a too large and poorly positioned bypass port in the cylinder.  The "stuffing that needs to be done is placing a wooden stick of a given size in the middle of the bypass port to reduce it's size...it works very well and fixes the problem. 
Nothing else discussed here will fix the burp, especially on an engine that has a burp drastic enough to make it quit.
This is Gospel...use the link Brett provided and follow the instructions...anyone that can use a screwdriver and an xacto knife (or even a pocket knife can) easily perform the mod. 
All of the other discussions are just window dressing.

Randy Cuberly

Randy,

Agree with you about the stuffer backplate. The original poster (Motorman) asked if they were still available and from whom. I was just answering the question asked.

I did state twice to do the bypass mod. As far as asking about the glow plug and prop, why not use the right ones to give the engine the best possible chance to run as well as it can?

-Chris

[Mike Keville]

. . . I still think this wood thing is some kind of inside joke . . .
MM

-------------------------------------------------------------------------------

Nope, no joke.  Like most all else recommended by Brett Buck, you can 'take it to the bank'.

[Brett Buck]

OK, just made the wood piece but the dimensions given in another thread were off for my 50th case. I ended up with width 1/4", thickness 1/8", length 1.278" still had to carve the face concave to fit the sleeve. Once the epoxy is dry I'll rough up the case and glue it in with JB weld. I still think this wood thing is some kind of inside joke, doesn't this kill the power by choking the bypass?

  Properly installed, it either has no effect on the power, or in some cases, a very slight increase. The reason it doesn't reduce the power is that the bypass volume is not the limiting factor in the power generation. One of mine has the entire bypass filled with J-B weld, and two channels routed out with a 1/8" Dremel ball head router bit - very very crudely. It certainly lost no power in the process. And the power right after a hard outside corner was infinitely higher since it quit otherwise.

    As always, *I didn't invent it*. I spent years on the topic and never really got anywhere (although I did notice that the engines that did it the worst seemed to have the deepest bypasses) and gave up. Frank Williams figured out the real cause (after trying several other things like mounting it with the cylinder inboard like he did with the ST60) in around 1993 or so. Before this it was all the usual nonsense, ranging from "it doesn't happen" to "oh, it's a tank/glow plug/fuel problem" to "that's not a problem, that's what it is supposed to do"

    It is not a panacea, and after you fix it, you can still have other existing problems known to plague the engine, particularly on profiles. Like:

vibration causing fuel foaming or severe airplane damage
poor fuel draw
poor leaky/shaky/unreliable needle/spraybar
crankshaft breaking
backplate wearing out or getting aluminum bits knocked out of it
wearing out the conrod
seizing from the wrong fuel
wearing out or siezing from a bad setting
wearing out the plain bearing section
fuel spray out the front end
overheating from muffler
distorting the case trying to mount a muffler
distorting the case/liner by tightening the head bolts unevenly
leaking backplate

    but it won't be burping because of low velocity in the bypass anymore.

     Brett

[Randy Cuberly]

Randy,

Agree with you about the stuffer backplate. The original poster (Motorman) asked if they were still available and from whom. I was just answering the question asked.

I did state twice to do the bypass mod. As far as asking about the glow plug and prop, why not use the right ones to give the engine the best possible chance to run as well as it can?

-Chris

Hi Chris,
Yes I understand and apologize if my post sounded critical towards you.  I was simply trying to clarify...again...for the less experienced folks that there should not be any misunderstanding about the semantics of "stuffer backplates" vs "stuffing" the bypass.

I agree with you about the prop situation.  However fix the bypass first then try some different props, which in the case of the Fox, will likely be an APC 10X5.  However other props can work depending on how big and draggy the airplane is.

Randy Cuberly

[phil c]

I have run the old reliable Fox .35 Stunt in about any configuration you can think of.  Never had a problem with them cutting out unless there was a problem with the fuel delivery.   My son and I was breaking one in on the plane by flying it rich.  Would cut out after about six laps.   Seems we had a spit fuel line.   Another time it was a bad fuel tank.   Have you tried changing tanks?

A lot depends on the particular case involved.  The different generations had different bypass depths.  The bypass depth apparently could differ significantly from case to case in any batch.  So when in danger or in doubt, stuff the bypass per the link.  All the cases had more bypass area than needed.

[Brett Buck]

A lot depends on the particular case involved.  The different generations had different bypass depths.  The bypass depth apparently could differ significantly from case to case in any batch.  So when in danger or in doubt, stuff the bypass per the link.  All the cases had more bypass area than needed.

   I noted that above, and over on the old RCO forum. It was really staring us in the face for a long time but nobody ever made the connection.
  Since it doesn't hurt anything, there's no reason not to just do it and be done with that issue for ever.

    A Fox is still about the worst choice possible for vintage 35-sized profile stunt planes, but I have long since learned that people are going to do it anyway, so might as well have a fighting chance. It would have saved me 4-5 airplanes back in the day!

   Brett

[Brett Buck]

Thanks for the help Brett, I consider you as a great ambassador to our hobby. Really appreciate connecting with someone that's knowledgeable and experienced. 

   That's very flattering and I do try to be helpful, but in this case I just read about it in Stunt News like everybody else!

    Brett

[Dennis Moritz]

In Philly folks fly a lot of Fox 35s stock. Dan Banjok won Old Time at this years NATs, flying a Galloping Comedian powered by a stock Fox 35. He has often won this or that at local meets flying Foxes. So have other club members. I don't fly them, so I can only report what I see with my lying eyes. Fuel is Powermaster 22% (50/50) 5% or 10%. Fuels we run in almost everything. We use thunderbolt long RC plugs or Enya #3s. Sometimes the pistons need to be lapped. Vibration is often an issue with these 1950s engines. The engines will burp. But if the plug is right and the fuel is right and piston/cylinder fit is good and the front bushing isn't worn out, the engine can be tuned so it won't burp. Of course I have heard of plugging the bypass port. A remedy frequently suggested for FP40s and Tower 40s. We also run those engines without messing around with the ports. They serve us quite well.

[RknRusty]

I too, really appreciate you experienced guys making sure we newcomers are clear on all of the info. In my case, l'll be mounting my first Fox, a 1958 Stunt .35 on a Yak 9 that's been on the back burner for too long. Since I've never heard the burp, I'm going to fly it as is at least once just to witness it. If I don't destroy the plane while witnessing, I will immediately plug the bypass.
I'm glad I have a couple of OSfp backups in line behind this Fox.

Rusty

[Joseph Lijoi]

In Philly folks fly a lot of Fox 35s stock. Dan Banjok won Old Time at this years NATs, flying a Galloping Comedian powered by a stock Fox 35. He has often won this or that at local meets flying Foxes. So have other club members. I don't fly them, so I can only report what I see with my lying eyes. Fuel is Powermaster 22% (50/50) 5% or 10%. Fuels we run in almost everything. We use thunderbolt long RC plugs or Enya #3s. Sometimes the pistons need to be lapped. Vibration is often an issue with these 1950s engines. The engines will burp. But if the plug is right and the fuel is right and piston/cylinder fit is good and the front bushing isn't worn out, the engine can be tuned so it won't burp. Of course I have heard of plugging the bypass port. A remedy frequently suggested for FP40s and Tower 40s. We also run those engines without messing around with the ports. They serve us quite well.

Keep in mind that this thread is about a profile mounted engine.  The Galloping Comedian is an upright mounted engine.  Im sure the nose on Dan's plane is very stiff.  Al Rabes Mustunt had an upright mounted engine on a profile.  Wynn Paul suggested that this be done to a Magician.  Both of those guys agreed that getting a good run on a profile is "virtually impossibe".

Maybe the inboard mounted profile will work.  To me a lot of these suggestions seem more complex than running a tuned pipe.

[Joseph Lijoi]

  Properly installed, it either has no effect on the power, or in some cases, a very slight increase. The reason it doesn't reduce the power is that the bypass volume is not the limiting factor in the power generation. One of mine has the entire bypass filled with J-B weld, and two channels routed out with a 1/8" Dremel ball head router bit - very very crudely. It certainly lost no power in the process. And the power right after a hard outside corner was infinitely higher since it quit otherwise.

    As always, *I didn't invent it*. I spent years on the topic and never really got anywhere (although I did notice that the engines that did it the worst seemed to have the deepest bypasses) and gave up. Frank Williams figured out the real cause (after trying several other things like mounting it with the cylinder inboard like he did with the ST60) in around 1993 or so. Before this it was all the usual nonsense, ranging from "it doesn't happen" to "oh, it's a tank/glow plug/fuel problem" to "that's not a problem, that's what it is supposed to do"

    It is not a panacea, and after you fix it, you can still have other existing problems known to plague the engine, particularly on profiles. Like:

vibration causing fuel foaming or severe airplane damage
poor fuel draw
poor leaky/shaky/unreliable needle/spraybar
crankshaft breaking
backplate wearing out or getting aluminum bits knocked out of it
wearing out the conrod
seizing from the wrong fuel
wearing out or siezing from a bad setting
wearing out the plain bearing section
fuel spray out the front end
overheating from muffler
distorting the case trying to mount a muffler
distorting the case/liner by tightening the head bolts unevenly
leaking backplate

    but it won't be burping because of low velocity in the bypass anymore.

     Brett

I take it that the inboard mounting didn't work.

[Dennis Moritz]

Dan regularly flies Fox 35s on profiles, including Ringmasters, these work quite well. He has won or placed high at Brodak, Huntersville and elsewhere flying Ringmasters in Old Time and even on occasion in Classic. Others in our club also regularly mount Foxes on profiles. If the Fox has a decent piston/cylinder fit, if the plug and fuel are right, and the tank and so forth are ok, the engines work. Some in our club think the softer nose on original Ringmasters, they use 1/16" ply and engine mounts that do not run past the engine cutout, absorb some of the bad vibes, actually improving the run. The Galloping Comedian does not provide much extra support for the engine. The engine mounts are secured to doublers, not the exterior of the body, as they would be in a conventional full body UC plane. The exterior dimension of the body is wider than the engine mount platform. Dan had to handle vibration issues with this plane. Which he eventually resolved. The ports were not touched.

[Brett Buck]

I take it that the inboard mounting didn't work.

  No, inboard mounting made it burp in insides instead of outsides! That was actually a key observation to the entire thing.

   The entire thing including the experiments and reasoning were in Frank Williams' SN article on this topic, I can't immediately find the issue but look in the 1993-1995 time frame.

     Brett

[Joseph Lijoi]

Dan regularly flies Fox 35s on profiles, including Ringmasters, these work quite well. He has won or placed high at Brodak, Huntersville and elsewhere flying Ringmasters in Old Time and even on occasion in Classic. Others in our club also regularly mount Foxes on profiles. If the Fox has a decent piston/cylinder fit, if the plug and fuel are right, and the tank and so forth are ok, the engines work. Some in our club think the softer nose on original Ringmasters, they use 1/16" ply and engine mounts that do not run past the engine cutout, absorb some of the bad vibes, actually improving the run. The Galloping Comedian does not provide much extra support for the engine. The engine mounts are secured to doublers, not the exterior of the body, as they would be in a conventional full body UC plane. The exterior dimension of the body is wider than the engine mount platform. Dan had to handle vibration issues with this plane. Which he eventually resolved. The ports were not touched.

Well Dan is an exceptional modeller/flyer and he knows what he is doing.  My local experts warned me but I did not listen.  I did not want to buy a reworked engine, and I was convinced that man it was good enough for Bob Gieseke and most of stunt history so what did they know.  At this point i was getting into control line again after flying 1/2a's as a kid.

Rollie McDonald told me me after watching me struggle at the  field "those things don't run with mufflers".    I said "but Rollie you almost won the Nationals in 195X with a Fox".

On thing that worked for me was putting the crakshaft in a chuck with a dial indicator and whacking it in the appropriate spot with a hammer. 

[Dennis Moritz]

Fly an LA25 on traditional 35 sized sport profiles. Ringmasters, Flite Streaks, Busters and the like. LA25s are usually no fuss, fuel and start. Great way to go. Fox 35s are a subset of the hobby. Almost a hobby in themselves. Problematic manufacturing tolerances and elderly design, (it's a cast iron piston/steel liner, non adjustable venturi, stock old style spade needle valve is an adventure) contribute to it's idiosyncrasies. Lapping pistons, truing up the front bushing (or replacing), fun projects for the experienced and capable. Also Foxes even when running well, vibrate, are shakers, lots of vibes, frequently bad vibes. Overcoming the weird harmonics of a specific Fox 35/airplane match (all engine plane combos vibrate differently) can be challenging, even daunting. I have been there. Steel mounting pads, aluminum plates on the backside of profiles, providing a cinch platform for mounting screw, bubble wrap tank mounts, velcro tank mounts and so on. Let your imagination run free, it might make a difference.

[Dennis Moritz]

Call Dan Banjok, bring it to Neshaminy. If the weather is decent, I'm sure Dan will take a look.

[Steve Fitton]

Call Dan Banjok, bring it to Neshaminy. If the weather is decent, I'm sure Dan will take a look.

What Dennis said.  Take it to the Neshaminy Park field and have the local genius look at it.  Dan can get anything to run!

[john e. holliday]

Well I  put the wood in the bypass, used the hottest plug I had (2004 Merlin), raised the tank all the way (1/4" above spraybar), used a 10-6 prop and leaned out the needle until it was starving for fuel on the inside loops. Still has the same problem, do one lazy 8 and poof engine quits at the top of the outside loop.

MM

Too much at one time.  You are supposed to make one change and then fly.   Too bad I can't be there in person to see your set up.

[Joseph Lijoi]

Too much at one time.  You are supposed to make one change and then fly.   Too bad I can't be there in person to see your set up.

John is right.  You are getting impatient.  The Fox has this effect on people.  Go back to the original set up that you had before you you posted.  Before you made a "stunt tank".   The point where you werre getting the "nice break on the insides".  Then run it with a blocked port and adjust the tank height from there.

[Dennis Moritz]

A chicken hopper might work.

[john e. holliday]

Wait til you have one that you have to move the tank opposite direction of normal.   Mine is an Enya .35.   Will not run right with tank set like a Fox.

[Jim Thomerson]

On an upright mounted Fox, the uniflow in the fuel needs to be maybe 1/16 to 1/8 either above or below the centerline of the tank.  I forget which.  Start out with it on the center line and adjust accordingly.  It is a very small adjustment.  Last time I set up a tank for an upright Fox was some six years ago, and I just don't recall.   

[BillP]

1/16" above in my house