Yoder808

Ok, I got my TH .46(Slimline Pitts Muffler) running great and flew it saturday, 1 flight, no dead stick. My other post is here [link=http://www.rcuniverse.com/forum/m_4777955/tm.htm]TH .46 ran fine upright, not sideways![/link] . I went to fly it yesterday, and it ran great, same as before, until I taxied out, and it died. I shook the plane, and I can hear the clunk is free. I started it again, and tried to taxi. Engine dies. A guy out there shook my plane, and tilted it nose up, nose down, nose up, nose down. It died in the same manner. Whats my problem? Lack of back pressure? It runs fine, as long as it isn't moving.

Yoder

Flyboy Dave

My Feedback: (21)

Pull the fuel line off the carb, and crank the engine over with the electric
starter....fuel should come out of the fuel line with a bit of pressure from
the tank....if not, you might need to plug off one of the outlets from
the exhaust on the muffler.

Lack of pressure is common with some Pitts style mufflers. []

FBD.

opjose

Yup...

I told you in the other thread that I've been through all of this.

All of the same problems and symptoms due to that Pitts Muffler and the T.H. Engine's lack of muffler pressure.

Closing the holes or stopping one up will not fix it either.

The default muffler does not altogether cure this, but it does improve things quite a bit.

A muffler with a baffle takes care of the problem altogether.



Bite the bullet and remount the engine with a stock muffler or something like the O.S. Pbox, etc.

BTW: I just tried out a MACS .46 tuned muffler pipe and it also seems to work fine.

NM2K

My Feedback: (14)

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Or cheat and mount a Perry/Connely VP-20 oscillating pump to the engine's backplate. These generally do not require adjusting of any sort and can cure a lot of low muffler pressure problems. Sometimes a little help is all you need.

bla bla

I think this guy is so green the last thing he needs is a Perry thrown into the works!

Yoder808

Thats true, I am green! I am was thinking about getting a VP-20 or VP-30 pump. What do you guys think about the VP-30, more or less fool proof than a VP-30? I can't mount my engine with the stock muffler. I am going to get a Saito 82a or a YS-63 eventually. I just need this motor to get me by for a while, ya know?

Yoder808

I've got some new needle valve o-rings on the way. They looked cut a little, from the first time I attempted to richen it, and the needle valve came all the way out. I am sure my clunk isn't stuck, but is it possible I put the tank in upside down?

BillS

Well … I hope not but have YOU considered looking rather than asking?

opjose

While worriesome, if the tank were upside down you would see the engine unable to maintain an idle (from flooding) or it would run until you accelerated.

You would also be likely to see fuel flowing from the muffler due to siphoning as well.

Never the less you should check...

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Again I've been through all of this, including the richening to the point of removing the needle.

You'll need either the Perry pump or to do something about the muffler.

I bit the bullet and installed the original muffler on one plane, a Macs on another and an OS baffled muffler on a third. All have T.H. engines.

All run just fine now, two are mounted inverted.

It's a fuel problem which you are trying to cure by richening the engine far too much to get fuel to it.

You will not solve it this way, you'll end up with the plane cutting out in the air at best. You'll be the proud owner of some nice matchsticks.

Dump the Pitts or go with the Perry pump.

But you should REALLY bench test the engine first, and run at least 1/3 gallon through it, as it sounds as if it is new.

You can make yourself a nice test bench with some scrap plywood, some tubing, fittings, a fuel tank, and some sheetrock screws.

This is well worth doing.

Yoder808

This engine has about 1 gallon through it, but it was on a Tower Trainer then. These problems didn't start until I put it on the funtana. Ok, I will buy a Perry pump, and machine some aluminum plugs for the muffler.

NM2K

My Feedback: (14)

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That could be true.

But, if it truly is a low muffler pressure problem, the VP-20 would be a simple solution and it requires no adjustment, or tapped pressure line like the VP-30. Unbolt the top two backplate screws, insert the VP-20, replace and retighten the backplate screws (capturing the VP-20), cut the fuel line at the appropriate point, fit to the appropriate fitting on the VP-20, and you are finished. Go fly.

All I can go by is what he says in his post. I have seen Pitts mufflers that actually provided a negative pressure pulse at the pressure fitting. No, I didn't believe it either until I saw it for myself. Removing the fuel line from the pressure fitting and letting it hang open was the solution. The carb was retuned and the engine ran just fine (Enya .40 baffle piston). That was back before engines came equipped with carbs so large that they truly did depend upon some assistance drawing fuel.

opjose

The Perry pump will help, the plugs WILL NOT.

Yoder808

Ok, its settled, I am getting a perry pump then... But Which one? I am skeptical about the VP-20, does it work well? Or should I just get the VP-30? Thanks for the patience guys!

opjose

The VP-20 requires a running engine to give it the vibration that is required to operate the pump.

Mounting is an issue as it must be done right.

The VP-30 is more difficult to deal with

See: http://saito-engines.info/body_pumps.html

IMHO it's easier to remount the engine.

Sport_Pilot

Just fill one of the exhaust tubes with JB weld, or crimp both of them. But if the engine is mounted sideways and you have even a little muffler pressure you should be able to tune the engine.

opjose

No it doesn't work.

Plugging the tubes does nothing with this engine, neither does crimping them.

The Pitts muffler is to blame. The TH needs some pressure.

The stock low pressure output muffler, will do even when the engine is inverted. The Pitts kills the engine every time no matter what you do.

Sport_Pilot

Then plug them up completly! Obviously restricting the exhaust flow will increase the pressure. Lots of people have used pitts mufflers with no problems, plugging or crimping the tubes is almost ritual. Now why doesn't the pitts muffler manufactures get wise to the fact that their mufflers are too loud and do not create enough backpressure?

opjose

Well obviously you cannot plug them up completely...

I've had the same problem as he has with the Pitts and the TH .46 engines.

I had the outlets crimped down to the point of being 1/16th "slivers", then I tried plugging one side or the other as well. No luck on several different TH .46 engines and serveral different Pitts mufflers. (I also ended up giving up with the same problem on an Evolution 1.0NX and Pitts inverted muffler...).

The muffler was not producing any pressure with this engine. It was as if the fuel tank was vented to the outside air.

As a result the engine will run, but it varies all over the place when the plane's attitude changed.

e.g. with the engine mounted sideways, making a right turn caused it to go rich, left turn lean, etc... due to the lack of pressure.

The pump does fix this though, as did switching to another muffler. The stock TH muffler did ok, but I had best consistency with a baffled muffler.

NM2K

My Feedback: (14)

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We know that if the engine is running, there MUST be positive pressure in the muffler. The real problem is that the pressure tap nipple is in the wrong place. I would remove the tap nipple, plug the hole with the appropriate size and length bolt, then drill and tap another location on the muffler. It's pot luck, so pick a place that is convenient for you to handle when flying the model. The chances of finding a null pressure location in a positively charged muffler is very low, so just about any other location will statistically have to provide better results.

Semco made a Pitts muffler some years ago with the exact same problem. Relocating the pressure nipple was the cure then too.

NM2K

My Feedback: (14)

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The VP-20 works well, does not generally require adjustment and is dead reliable. The VP-30 is a PITA to adjust and seems to be constantly changing. I gave up on the VP-30 pumps except for very large glow engines. Engines large enough to ignore the variations that occur.

If you use a pump, you DO NOT need to plug your exhaust pipes. All that will do is reduce the engine's performance.

Furthermore, do not use muffler pressure when using any pump. This will upset the regulator's functioning properly and will lead to mediocre results, whether the VP-20 or 30 is used. Just run the vent line down the face of the fuselage and toward the air exit in the bottom of the cowl, assuming you are using a cowl.

There is no way that your engine can run without shaking the VP-20 pump sufficiently to pump fuel. Worry not. Just be sure to follow the instructions about orienting the pump properly. That is the only caveat.

Yoder808

Sweet. I will go get a VP-20 tomorrow from 'da LHS then. I am REALLY thinking about just biting the bullet and getting a Saito 82a, but I REALLY need a better radio. I am using a (please don't laugh) Tower Hobbies 4 Channel, with TH TH-53 Servos. I was going to get a Futaba 7C or a JR 7202. But, the 7C doesn't do dual elevator halves w/mixing, and the 7202 I just don't know about. I think I am going to get a 9C Super. I really hope I can get this engine problem worked out soon, it sucks not being able to fly when ever I want!

NM2K

My Feedback: (14)

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I don't laugh at anyone's equipment. As long as the rig range checks safely with and without the engine running and I'm sure it will when working properly. It will do the job.

I have a JR X-347, an 8103 and a 9303, but I also have a used Hitec basic four channel and a bunch of radios that came with RTF models. The latter are surprising in their utility.

I hate to recommend a pump, but sometimes you get boxed into a corner.

The good thing about the VP-20 is that it can be used with just about any engine, whether two or four-stroke, big or small. I use VP-30 pumps too, from time to time, so I'm not against them. I've also used the Cline regulator, which works just fine with crankcase pressure on a two-stroke. But that is pretty expensive when compared to the VP-20.

Yoder808

Yeah the Cline and the Iron Bay seem quite overpriced, but that is expected I guess when you have a virtual monopoly on a niche market.

Flyboy Dave

My Feedback: (21)

The Cline...at $60.00, has to be the biggest rip-off in the r/c marketplace.

That piece of plastic probably cost's about 20 cents to produce. [:@]

FBD.

opjose

There is no need for you to use flaperons with the Funtana 50X. You simply will not gain much by it, and you really also need to use differential mixing with the flaperon setup.

The Funtana alreay is very light and tends to "float" anyway. I have this configuration on my Funtana 90S and never really use it.

The Saito is also overkill as the T.H. .46 will give you slightly more power than the Saito .81.


Why the reluctance to remounting the TH .46 and using the stock muffler?

It fits just fine?

At worst you may need a new cowl but you may not.

Next best alternative is to use the pump IMHO.

I'd prefer to fix the original problem, then improve things with the pump...