Help! Can't keep TH .61 running inverted in a GP J3 Cub!

I am struggling with a problem. I have a Tower Hobbies .61 engine mounted inverted in a Great Planes J3 Cub (12x7 prop) and I can't stop it from dying
in the air. Damn thing runs on the ground without a problem. It will run through a whole 400ml tank without a hitch. Have tweaked both high and low settings on the engine so many times I'm surprised I still have my fingers. Every time I take off with it, it starts to burble in the air and dies, like it's too rich or something. It's running about as lean as I can keep it running on the ground without worrying about damage to the engine. I'm at my wits end ... can't even get 3 minutes out of it in the air. The engine has about 2 hours runtime on it now, almost all on the ground.
Anyone have any experience with this? There are a couple unknowns on my part, I've only been flying a year. I have two other gas engine planes and two electrics. The gas planes are using O.S. engines (.46 and .70FS) and I haven't had a problem with either of them. This is my first Tower Hobbies engine and also the first engine I've ever mounted inverted. (double whammy)
I've done the usual checks and the gas tank isn't mounted higher than the carb, yet it seems that it is loading up in the air ... but it's fine on the ground.
I've tried multiple glow plugs... A3, A8, medium hot long and short with and without idle bar. The book on the engine recommends an A8 I think. Had the best results in the air with an A3, but the best on the ground with an A8....go figure.
Are some engines just not capable or not recommended for inverted mounting?
I need some suggestions ...
Storm
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I have heard that Tower Hobbies has excellent customer service with their engines, i.e. engine doesn't run right, they will replace it. Kind of makes me interested in their engines.
It really sounds that you have a fueling system problem which could be a number of different things. I had a similar problem that turned out to be a restricted muffler pressure line at the tank. It would run fine on the ground, but once in the air it ran sick. After I discovered the crimped brass line it solved the problem. The next day at our flying field another guy was having a similar engine problem in flight and I mentioned my muffler pressure issue. He checked and his muffler was loose.

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Have you tried 1/2-full throttle on the ground while holding the plane still, thereby duplicating the "load" flying places on the engine? Sounds almost like if you have it set close to lean on the ground, it's set too lean for flight and could be flaming out due to a leaning problem. If you have an IR temp gun, spec the temps after some grounded runtime and after a few minutes of airborne runtime and see if she's overheating. Could be an airleak somewhere causing an overlean as well.................
My $0.02
Doc
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Ted shuffled out of his cave and grunted these great (and sometimes not so great) words of knowledge:
After you "peak" your engine out (and back off about 300 rpm ), with the engine running at full throttle, pick the plane up and and point the nose of the plane straight up. The engine should not change rpms if the high speed needle is set properly. If the engine speeds up, richen the engine about 1/8 turn and do the nose up test again until it does not change rpms. If the engine slows down, lean the engine about 1/8 turn and repeat the test until there is no rpm change.

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Are you sure that you've got this the right way round?
An engine often speeds up if it leans out which is what would happen if a rich engine was pointed "nose up". An engine too lean will cut when subjected to this treatment.
Malcolm

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Most times, the design of a Cub causes the tank to be far above the carb when you are flying level. Also, if the tank isn't well isolated, you can get resonances as the engine speeds up that you won't get on the ground.
Try flying the plane at well less than full throttle and see if it still has the problem.
You might also try a fuel regulator such as a Cline or Perry.
--
Paul McIntosh
RC-Bearings.com
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Thanks for the reply. All suggestions are good suggestions. The engine seems to be have most of it's problems in the mid-low range area. I can keep it running longer, but not permanently, at higher throttle. The engine is a little much for the plane to begin with. A hot .46 would keep it in the air, I'm sure, but the .61 I've got in it is overkill. I'd love to be able to run it around 1/2 throttle or less ... in fact, I'll probably have to.
I'll check the tank again, but I've already checked once to make sure it wasn't sitting above the carb.
I'll look into the fuel regulator ... anything I can eliminate from the system will help.
Thanks,
Storm

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If all else is in good condition, i.e., fuel lines, pickup tubing in the tank, etc., it has to be a tank placement issue.
Remember, if the tank centerline is higher than that of the spraybar in the carburetor, you are going to have flooding issues. In fact, it would be good if the tank centerline were up to 3/8" below the carb spraybar.
Another thing to check is that the backplate is tight. My TT engines require constant inspection of this particular part. Those screws love to wiggle loose and cause mysterious carb problems.
Good luck in finding the problem.
Ed Cregger

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wrote:

Huh. Only got a Pro .36 and a Pro .46 but after I put the hurt on the bp fastener bolts they done stayed put on both. If I had a problem I'd use some a that blue locktight, it works fine and you can still remove the bolts if necessary.
Texas Pete
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I'd bet money that the clunk has separted from the fuel line. On the ground, the engine still gets fuel, but in the air inverted, it's sucking air. When inverted, it's the weight of the clunk that keeps the pickup in the fuel.
Regarding the Tower engine, I'd send it back to Tower for a refund. Stick with the best: OS Max.
Ciao,
Mr Akimoto
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Are you running a pitts or non-standard muffler? These sometimes have two outlets and don't provide enough muffler pressure. Try plugging one of the outlet holes and see how it runs.
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I'm a neophyte to this hobby; I don't even have my trainer completed yet, so take this with a grain of salt.
Being a new guy to this, I am trying to read everything I can to learn some of the basics of RC aircraft. One thing I read recently (but can't recall where) was something from another guy with a Tower .61 with a similar problem. The engine wasn't mounted inverted, but he still had problems keeping it running. The solution turned out to be something about the carburetor not seating properly in some Tower engines. Someone suggested the application of a little silicone to help it "seat" properly. The problem was apparently solved.
This is especially interesting to me because the engine I will be running in my unfinished Tower Trainer is, in fact, a Tower .61 ABC BB. If I have the described problem Ill be wanting to try the solution I mentioned, but I have no idea what type of silicone to apply or where to apply it.
Anyway, that's my half penny's worth.
Harlan

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so
some
the
was
in
have
The silicone would be applied round the opening where the carburettor goes into the crankcase. This joint usually has an "O" ring and a little silicone sealant, silicone "instant"gasket material or even Blue Hermatite jointing compound will ensure an airtight seal in this area.
Malcolm
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A few options to check, make sure your brass lines are not cripmed, that your fuelk lines have no pin holes. Also something that I have negelected to check, make sure the clunk in the tank is at leats 1/4 in free. Also make sure the fuel tank is well secured in foam, that no vibration is allowed, this can effect the fuel with bubbles. GOOD LUCK
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And remove the remote fueler and replace it with a third line into the tank that slips over a bolt with its head cut off when you are finished refueling. Damned refueler valves cause a mega-amount of trouble and flame-outs. They are trouble causing, crash inducing, junk.
Why? They fail to close completely and cause all kinds of problems, regardless of who makes them or sells them. Many a good engine and model have been crashed because of refueler valves that refuse to seat properly. Don't ask.
Ed Cregger
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Not only that, but no matter the design, they are another source of restriction in the fuel line.
--
Paul McIntosh
RC-Bearings.com
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After checking all the suggestions and coming up with zip on this end, I decided to borrow a friends O.S. 61 and have mounted it identical to the Tower Hobby engine without changes to the fuel system. I am just waiting for weather (raining here) to try it and will update the group with the results. If it flies without trouble, I'll mount the TH .61 in another plane (not inverted) and give it a try. If I have trouble with the O.S. as well, I'm tearing the whole fuel system down....
Just a list - No vibration (no bubbling) Don't have a remote fueler installed. Muffler is not restricted or loose and only has one outlet connection for pressure back to the tank. Runs fine on the ground at all throttle settings. "Pinch" test passes. Engine appears to be properly set. Tank centerline is not above the carb. All screws tight and locktighted ... is that a word? Carb appears to be seated well ... even added sealant to be sure... Clunk is not separated and moves freely. Fuel system appears to have no leaks, no fuel line pin holes or crimped lines. Needle valve appeared OK, but changed it anyway....
And still, it burbles and dies in the air in approx. 30 secs to 1 minute after takeoff. I once leaned it out as lean as it would run on the ground and got about 3-4 minutes out of it ... probably shouldn't have tried, but at that point I didn't care anymore. The fact the plug is almost always wet with fuel ( tried several fuels -- running Omega 15% ATM ) kept pointing to rich, so I figured I'd give it a shot. Sucked too ... just as I was becoming elated that I'd found the problem was when it decided to die on me. If I didn't still have to land the thing, I might have felt like throwing the remote to ground!! JK On things for sure ... I can land this thing, dead stick, with my eyes closed. Lots of practice....
What would cause an engine to move severely rich during flight that it doesn't do on the ground? Weird... Is it even remotely possible that air moving across the carb is causing a vacuum venturi? I guess I could check that easily enough, if the engine ever gets back in the plane....
Keep you posted .....
Thanks all!
Storm

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When you are running it on the ground, are you raising the tail up like it is in flight?
--
Paul McIntosh
RC-Bearings.com
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Yep ... even had the buddy I'm borrowing the engine from hold the thing and maneuver it around like it was in the air. Stayed running...go figure. Hoping for good flying weather tomorrow or Sat.
Storm

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The first thing to understand and acknowledge is that the engine has no way of knowing that it is running inverted. It is just a machined lump of materials.
Assuming that the engine is in perfect mechanical condition, i.e., all fasteners are at proper tightness, there are no airleaks, the engine is fitted with the recommended glowplug, propeller size is within spec and the proper fuel is being used, the problems that you are having must be related to the fuel delivery system.
A setting of the needles in an inappropriate manner could also contribute to the problem, as well as the engine not being properly broken-in and not being ready for normal service.
While the initial handling and starting of the engine is changed somewhat by the fact that it is inverted, after it is running, its operating position is of no consequence. The latter fact is difficult for some folks to work into their noggin, but it is true.
Stale or contaminated fuel is also a possibility, if you haven't addressed this as of yet.
Do not rely upon the model's manufacturer or designer to have set up their model in proper fashion, i.e., tank height/vibration isolation.
One of the things that I learned long ago was to never let any part of the fuel tank touch any solid part of the model. It will lead to fuel foaming, which is a bear to detect. Why? Because when the model is sitting on the ground, the fuel may not foam, but as soon as it takes off and is in the air to freely vibrate as it pleases, that is when the fuel foaming begins.
Obviously, with what I have written above, it is clear that any model that has its fuel tank neck sticking through the firewall, is designed poorly and is prone to problems.
I have seen many folks quit the hobby because they would not believe me on this topic and they insisted upon using the factory setup - became discouraged at constant flame-outs and then gave up in disgust.
I do not sell fuel tanks, therefore there is no reason for me to lie about such a thing. There is no profit motive involved at all. But some folks simply cannot believe that their model's manufacturer is either inexperienced, stupid or all of the preceding.
Oh, and even if nothing is touching the fuel tank, or its brass/aluminum fuel lines, it can still vibrate for other reasons, such as having the foam that is packed around it too tight. No, rubber banding it to the floor won't work either. <G>
I did my bit by telling you. What you do is up to you.
Ed Cregger
P.S. This is a message to all newbies, not just the original poster. In fact, some of what I have said may not apply to the original poster at all. I know nothing of his experience level.
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