I have Magnum 91 RFS Four Stroke in Showtime 50; use Tower 15% Premium Fuel and 14x6 APC.
It is just about to be broken in - a gallon of fuel ran through.
Also it is mounted inverted.
My problem is: it is tuned on the ground. In the air it loses power, when I fly straight up it picks up some. But when I fly inverted it is working really well - the way I wanted. Good rpm’s, strong throttle response.
Does anybody can guess what could be a problem?
I am thinking to install "Perry Oscillating Pump" to make more equal fuel pressure when it is running in different orientations.
What do you guys think?


Pasha.

Sounds like you have a tank height problem among other things

The tank must be centered on your needle valve for aerobatic flight

Besides setting up your tank at the right height, check your clunk, it may be sticking in one corner and flopping down when inverted. Could also be a hole in your clunk line allowing air in when in the normal mode of flight and when inverted, the line could be immersed. Little things count.

Cheers,

Chip

Hi!
You better check your tank! Have you mounted the tank correctly?

Also see to that you use a Uniflow set-up!
Or...get a Tettra "Bubbleless" tank.
A pump is not that good.

Thanks guys!
When troubleshooting - every idea counts!
The tank is standard and in standard location, so I hope its height is not a problem.
But, who knows! I will check it out with a little more care.
Clunk line needs to be checked for sure! Always a good idea! Thanks.
Sorry to hear that pump is not that good – I was kind of counting on it to hide my problems. J

Also, I use “Great Planes� Easy Fuller Valve. The front of the tank is almost sticking out of the fuse in standard hole. Then fuel line goes back into fuse to Easy Fuller Valve. Then it goes back out of the fuse to the engine. That configuration makes fuel line a little too long with one sharp turn and, may be cause problems in fuel delivery. I did not like from beginning, and I think I need to redesign it.

Thank you all guys,
Pasha.

Pasha,

I just bought a Magnum 91 RFS and am in the process of ordering my Showtime 50. I was looking for people with the same setup.

1) I was happy to see you did not have issues with CG

2) Second concern was the tank location and height since the engine has to be mounted upside down.
I have downloaded the Magnum manual and read:

"Ideally, the stopper in the fuel tank should be even with the high speed needle
valve or just slightly below it. Some models will only allow the fuel tank to be
mounted higher than the ideal location. A fuel tank that is positioned higher
than the ideal location usually doesn't pose any problem except when it is
mounted excessively higher and/or is used in conjunction with an inverted
mounted engine or during extreme aerobatic flight. If you mount the engine
inverted, we strongly suggest lowering the fuel tank so the stopper assembly
is slightly below the high speed needle valve. Doing this will prevent fuel
from siphoning into the engine and flooding it when the fuel tank is full. If
you cannot lower the fuel tank far enough, we suggest lowering it as far as
can be allowed in your particular application."

I will probably get mine in about 2 weeks.
I will be talking to some "experts" at my club and find more about this. I really think the pump could make a difference.

Please keep me posted if you find anything on this issue as it is one I anticipated.

Thanks,
Jean-Yves

The more amount of stuff you put on your engine ,the more things to fail . Pump ,fueler , remote igniter, ect ,ect. If it goes straight up and runs great says you don't have a fuel delievery problem......Sounds like your tank is a little higher than your carb and your set very rich. Vertical and inverted leans out the mixture to run better. You need a better tune and provided running great up right and vertical and inverted doen't lean out engine to much..

Jean Yves,


I have a slight problem with this statement...

If the fuel tank is a classic one, with the stopper smack in the middle of the front, it is OK...
But most tanks made today have the stopper placed higher, or even slanted.

What determines the uniformity of the fuel supply is the average fuel level; not the tank stopper hight.


So you should use the center-line of the tank as the reference; not the stopper, or wherever it was located by the manufacturer of the tank.

...As Jim (w8ye) and others wrote.

I am looking at the Sullivan Rectangular tanks. The stopper appears to be below the center line. And since I want to give Dar benefit of the doubt (this hole thing is new to me) I'll have both statements true and put all chances on my side.

Now... if a quick filler is used, like in Pasha's case (and my future case) does the height, relative to tank center line and carburator will also have an effect on the flow?

Jean-Yves

I think that tank center line is what almost everyone uses.

Well if its in a standard location, its probably to high. Most of my planes run inverted 2 & 4 stroke inverted engines. You will fool with that thing until the cows come home unless you lower the tank.

Jean Yves,


The tank level determines the average fuel level.

If the tank center-line is at the carburettor jet level and you adjust your engine to run a bit rich with the tank half full, your engine will be a bit richer as the tank is full, but will never be lean, even if the engine is run until the tank is near empty.


The latitude given; i.e. 'tank center-line slightly below carburettor jet/center of carburettor barrel', is because most fliers will use the top ~3/4 of the tank and will prefer not to fly until the engine actually stops from fuel starvation...

Adjusting the mounting to center-line will put the least risk of; 1. A lean situation and 2. flooding the engine when it is just sitting there, waiting for your turn...

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

I began a thread about one year ago, stating most ARFs and kits DON'T take the fuel level into account, in their design....
Very often, it is beneficial to change the engine mounting from what the plans say, to get the levels closer... It is like the model designers plans put appearances and ease of construction, at a higher precedence to actual flyability...

I just read on a thread in 3DFlying about the Perry pump.
http://www.rcuniverse.com/forum/m_15...tm.htm#1536441

Mixed fellings about it. It uses vibration to deliver. Some people reported tuning was more difficult, others reported that vibration made it behave eratically, whereas someone else was using a mount with cushions and no issue, etc.

One person recommended a regulator instead, from http://www.ironbaymodelcompany.com/i...es/Page438.htm

Have any of you guys used it?

Pasha, since I recall readind in another thread, you have left the tank in the Showtime 50 at stock location. If you go back to that "showtime anyone?" thread, some people were using other 91 4-c inverted engines, but had moved the tank location over CG and were flying the plane very well. Since I do not have the ST50 yet, I cannot see if that location is lower than were it is now (right behind the firewall it seems).

I might go with the regulator after digging a bit more about it.

Jean-Yves

Jean Yves,


Even more important; setting the tank center-line at the carburettor jet/center of barrel level, will make the engine run equally rich, whether the plane is flying upright, or inverted...


This is the prime motivation for this mounting scheme, in addition to fuel pressure uniformity.

I used the word vibration for the peery pump, but it was oscillation. Here are some tech notes from Tower Hobbies.

Perry's Oscillating Fuel Pump is recommended for 4-Stroke and
Giant Scale 2-Stroke Engines.

FEATURES: This Pump works off oscillations generated by the engine.
Oscillating pumps will also work on inverted or side-mounted engines.
This pump can be used with ALCOHOL BASED FUELS ONLY
This is the version called the "silver hex screw".

INCLUDES: One Oscillating Pump
Mounting Plate, Screws and Instructions.

SPECS: Pump is 3/4" in Diameter and 1 7/8" long

COMMENTS: Each time the engine fires, the pump reacts with a short rotation
in the direction opposite of the propeller rotation. This will
only work if the pump is mounted in line with the arc of the prop
and about 1.5" from the crankshaft centerline. 10-22-98kzh
ir/jl



There is also a good Saito page on the two items (Perry Pump and the Iron bay Fuel Regulator): http://saito-engines.info/body_pumps.html
One important thing that is mentioned:

The advantage of the above systems is that fuel will not run through them when the engine is not running. If you have a tank that is considerably higher than the engine, with the standard muffler pressure setup, or the Perry pumps mentioned below, fuel will run downwards through the pumps into the engine when the model is parked and flooding is possible. This does not happen with the Cline type regulators

Jean-Yves

Dar,

What I have read so far confirms what you are saying and it makes sense. In my case the stock tank is 11oz and with a Magnum 91, I will probably run it down quite low unless I relocated a bigger size tank. I metioned the Sullivan flex tank above because they say it can be reshaped with a heat gun (to what extent?).
I will get the plane first to see if the tank can be relocated then, last option is the fuel regulator. Don't think the regulator can hurt. (it will surely hurt my wallet though).

J-Y

This past weekend two new Venus showed up at our the field. One with a saito 82, one with a Mag 70. No fuel or runing problems reported with the Saito set up. The new Mag has about 1 1/2 gal run throght it. Idles bad. Will run forever at full throttle.. This engine is inverted two. Moved Mag 70 to sideway. Now it is in the correct possition to the fuel tank. Will report later after I have tryied runing. Should not have a fuel problem. You never know. I should have knowen better in the begging. Oh it looks terrable sticking out he side[:'(]

john see you at the field.

Jean Yves,


I am a firm believer in profit; a capitalist, if you will...

From a cost perspective, the Cline regulator, which uses a $5 gross (about $2 for them), Walbro carburettor diaphragm as its main component, along with cheap plastic castings and cheap fasteners, should have been fairly priced at $12-14, leaving Mr. Cline enough profit, since he is doing it all on his own.

It costs an outrageous $60...


The Iron-Bay item seems to be made of better external items; some metallic, but it is still based on the same Walbro part...
A fair price for it would have been $16-18. It costs $45.


Sure, they work pretty well, but I hate being profiteered...


Even with a demand based system, like those two, your engine will still run richer, it the tank is high and leaner if the attitude places it low, but it will be to a smaller extent than without a regulator.

The Perry oscillating (or the normal type VP-30) pump is indeed a positive displacement device. You operate it, you get a 'spritzing' of fuel...


Getting everything in the proper level is easier and cheaper than any pump/regulator...

If i use a Perry pump, can i remove the mufler restriction? Then, i don´t will need pressurize the tank more.. correct?

Hi guys,

Wow, there are a lot of comments! Sorry I was busy with work...it
I am sure this topic is important for almost every airplane.
I reviewed the fuel system on my Showtime 50 with Magnum 91 RFS.
Tank is in a good shape all fuel lines are clean. Clunk is just 1/4 inch from a back plate of the fuel tank. So everything is good with it.
I took it out for another day flying. Great time (Here is my big happy smile). First flight - I leaned it out a bit - everything seems to be perfect.
But second flight - same thing: lost power due to running reach in up side up position and excellent power up side down.
Landed tried to lean it a little more and rpm's went up.
So it is either still tuned a bit too reach or engine gets more sensitive to needles setting once it gets hot (or warms up).
I have both Perry Pumps, but can't find nice spot to install them, plus I am not sure that is the best way to solve my problem.
I also notice that stock location of the fuel tank is a little high for inverted engine installation.
I can see two solutions for me:
1. Mount engine horizontal - I need a new cowl
2. Get a regulator - which I think I will really like - I have YS63 and it is just super reliable engine, for which fuel tank location is completely insignificant.

1. Will cost me ~$20 – but it is backordered.
2. Will cost me 51$

I am still thinking.

I Mounted My engine horizontal. No change??????????????????[:-] I dont understand it and His (My friends) satio just keeps runing. I now have my tank in the correct possition for a horizontal Mounted engine. It just will not run right. theirs a spot just under half throttle were it will die, and I mean right now. Every time?????????? It does not speed up and die, it does not slow down and die. IT just dies everytime.[:-]

At the field to day several people tried, no luck[&o]

I'm sending Mine back to Tower in the A.M. Wish Me luck.

Unhappy in missouri
john

Dar,

Thank you very much for the advice. I will follow it. Seems like you've bee there and seen it.

Jean-Yves

You're welcome, Jean Yves.

That's what we're here for - sharing experience.


Good juck, John.

Tower stated they did not want the engine back, try Global. Global said I could send it back if I wanted to. They required all paper work including invoice. This will be no problem for Me. They also stated that they were backed up with these engines being sent back.
You just get what You pay for, If I would have payed for a Satio I would be flying now.
We must not forget that this is a hobbie, (fun).
john

Jship and Pascha,

I am no engine expert and I have received my first 4-stroke (Magnum XL .91 RFS). Have not used it yet.
I came across a manual on the net that seems more complete than the one I received in the box: [link]http://media.hobbypeople.net/manual/210970.pdf[/link]

Take a look at page 8 (last page). Magnum suggests that the valves be reset after the first hour of engine run-time and checked every 8 hours of flight time.
You will need to remove the rocker cover and use feeler gauges; but it is well explained.

This might help... Good luck.

Jean-Yves