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

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.

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

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.

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.

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

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

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

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

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.

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

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

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

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

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

Not only that, but no matter the design, they are another source of restriction in the fuel line.

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

When you are running it on the ground, are you raising the tail up like it is in flight?

On Wed, 12 Oct 2005 22:33:20 -0500, "Stormlord" wrote in :

It is now. :o)

I know the feeling. I have an OS 1.20 SC that gave me too much practice with deadsticks. :o(

Thanks for the update and the neologism.

Marty

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