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Old Dec 15, 2012, 09:12 AM
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nside the gas fuel tank, there is the vent line that is open to the atmosphere, so air is free to be drawn inside the fuel tank, so normally air leakage problem will not be from this line. The air drawn inside from the vent line should not be absorbed by the clunk since it is normally submerged inside the fuel.

The refill line is supposed to be capped off so no air can enter the fuel tank from this route. but even if this is a leakage in this line, can the air entered the tank through this route since the the other side of the refill line is submerged in the fuel, therefore the pressure of the fuel which is heavier should not allow the air to enter, so leakage from this line cannot cause problem, can this assumption be correct?

the last line from the fuel tank is the line that connect the clunk to the pump, I check that inside the tank the clunk and its fuel line is properly connected and submerged, and the line going out of the tank to the pump looks very fine to me.

But now there is bubble existing the brass tube of the tank stopper. So how and where the bubble comes from or created?
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Old Dec 15, 2012, 09:43 AM
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Originally Posted by earlwb View Post
But it may be that our USA blends of gasoline with all those extra chemicals such as butane and propane in it tends to be more sensitive to it.
Heck.... I didn't count on Butane and Propane to be present in your fuels....
I have experience with that in Heavy Fuel Oils to artificially (it is actually cheating of the fuel suppliers, illegal but impossible to prove) lower viscosity and that creates huge problems in pumping systems because we need to pre-heat those fuels at typically over 250 F.

Pumping gas containing Propane or Butane in a (high pulse frequency) membrane pump, that would be the same as shaking a soda-bottle, and in that case, yes it is very likely for bubbles to appear, especially in those high ambient temperatures.

My apologies for maybe putting somebody on the wrong foot.

The fact that a hanging free pump creates more or less bubbles however is not conclusive to the vibrations being the cause: it still is possible that strain on the fuel conections can cause very small airleaks, especially with the somewhat rigid Tygon Hoses. I have had a lot of problems with that in my gas powered helicopters.
Having said that: an occasional bubble should not be a problem, it might cause an incidental hickup of the motor. But foaming of the fuel in the tank, maybe it is a good idea to check your prop-balance. Experimenting with ignition timing could also help, but I suggest balancing first

Brgds, Bert
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Old Dec 15, 2012, 09:44 AM
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after closer observation, the bubble occured in the line from the tank to the pump, is indeed not coming from the tank, it looks very much like it is gerenated from the pump. So the pump is actually and possibly the cause of all bubble. The bubble seemed to be easier to be pushed into the line towards the tank; but much less or no bubble pushed into the line goes to the carb.
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Old Dec 15, 2012, 09:46 AM
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richen both needle more seems to be helping the higher RPM from quiting. But now is already LSN 7out, HSN 3 out. Wonder if I was heading the right direction or something else?
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Old Dec 15, 2012, 09:52 AM
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Originally Posted by kentli22 View Post
Brutus,

I am not capable of fixing the pump if there is a leak or any problem. I can only go buy a new one if I must suspect the pump has a problem. I don't think anyone will fix it for me, and I am not sure if the manufacturer has any interest to fix or repair anything.

Most likely, yes you are.... if you can disassemble the pump and put it back together the same way, that takes care of the mechanical skill.

Then you need access to a nice flat piece of glass and some very fine grinding compound (carborundum paste), grade 600 or finer (higher number is finer grade).
Carefully apply a bit of grinding paste on the glassplate and smear out in an even film. Gently rub the sealing surfaces of your pump in a circular motion over the glassplate, until all machining marks are gone and a nice smooth and flat surface remains.

If you have access to somebody with a machine shop, chances are he has a trueing plate, and in that case it is preferrable to use that instead of the glass plate.

CLEAN VERY THOUROUGHLY!!!!!

reassemble

Done.

Brgds, Bert
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Old Dec 15, 2012, 09:53 AM
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"Having said that: an occasional bubble should not be a problem, it might cause an incidental hickup of the motor. But foaming of the fuel in the tank, maybe it is a good idea to check your prop-balance. Experimenting with ignition timing could also help, but I suggest balancing first"

when the rpm is higher, the vibration is stronger in which the idle is the most calmest. is this the sign that my prop is not balanced? I am using 12*6 wood prop.

With my other gas engines, the higher rpm seems to produce less vibration than lower rpm.
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Old Dec 15, 2012, 10:10 AM
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Usually model airplanes have a resonance frequency that is closer to the idle RPM than to the full RPM.

Therefore, normally most vibrations are visible at lower RPM/idle.

So yes, your case MIGHT indicate that there is a balance problem.

Only way to check is to properly balance the prop and see if vibrations at full throttle reduce.
If it doesn't help, it doesn't do harm either....

Brgds, Bert
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Old Dec 15, 2012, 10:25 AM
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kentli22, you stated earlier that you had some bubbles coming from the fuel tank to the pump/regulator. You want to try to get that down to no bubbles. There may be a pinhole or loose tube inside of the fuel tank, or it is vibrating too much and getting air in through the pickup clunk. What I do is use some small Zip Ties and use them to clamp all of the lines inside of the fuel tank. The Tygon tends to get extra soft after a while and it can get more loose then allowing for air to get in. I also use small clamps or Zip Ties or pieces of wire to help clamp the fuel lines onto the fittings outside of the fuel tank too. With the wire you have to be careful not to cut the tubing but still apply some pressure to keep the tubing from slipping off.

Fortunately the pump/regulator is amazingly simple on the inside. There really isn't anything complicated inside. The pump half has a diaphragm and a gasket. There are two little flapper valves on the diaphragm that you align with their respective holes in the pump body. The flappers serve as one way valves, they allow fuel to flow in one direction but not the other.

On the regulator half side of the unit, there is the diaphragm and gasket too. But the middle of the diaphragm has a metal disc with a little knob on it. That little bump or knob pushes down on the metering lever opening the valve when the fuel is low inside, When the fuel fills up the reservoir, the diaphragm expands out and the valve closes from the spring pushing against it.

The metering lever is really just a lever. It has a fork on one end to hook the fuel inlet valve and can move it up or down a little bit. There is a spring that pushes against the lever forcing the fuel inlet valve to close off the port. The fuel inlet valve looks like a surveyors' plumb bob.The pointed tip actually is a hard rubber tip.

When you open up the unit, you check the outer edges between the mating surfaces and see if they are smooth without any tooling marks that could let air in or fuel out. You can use a piece of flat plate glass as a surface with some valve lapping or polishing compound on it. You move the part to flatten and smooth out more in circular figure 8 motions on the plate glass for a little while. Clean the part and check it to see if it is smooth or not. Then repeat as needed. There are really only two surfaces to check and that is on the pump/regulator body itself. The outer cover parts don't need to be checked.

Now it can be tricky to remove and install the metering lever and fuel inlet valve as you sort of almost need three hands to do it. That spring can sometimes be a hassle to get back under the lever as you reassemble it. It tends to not want to go back in.

Things to look for if you open the pump/regulator unit up, is the little flapper valves not sitting flat and having their edges curling down so they don't seal as well. The metering lever may need to be bent up slightly if it got pushed down too far. The OEm metering lever is made from a softer aluminum alloy and sometimes it gets bent down slightly. That causes the engine to flood as the pump is now now regulated. The regulator diaphragm can become stretched out too and stop regulating. Sometimes a little tiny bit of debris gets caught under the fuel inlet valve causing it to stop regulating too. Usually when I remove the fuel inlet valve I don't see anything, but it was there. As it works OK after I reassemble it.


The pump side of the pump/regulator unit. You can see some scratches in the surface that could lead to air leaks or fuel leaks.
Note that one hole for the flapper valve has a tiny scratch mark that leads to the outside. That scratch going to the hole could allow air to get sucked in causing air bubbles to occur.


The regulator side half of the pump regulator unit


The pump diaphragm in its position on the unit


Here are a couple of the regulator diaphragms and what they look like. The older one is on the left and it has stretched out a little.


I like these teflon pump diaphragms, but they may pump too strongly in some cases as the teflon ones pump the best.


But the blue ones work pretty good too
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Last edited by earlwb; Dec 15, 2012 at 10:29 AM. Reason: typo corrections
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Old Dec 15, 2012, 10:38 AM
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Yes Bert here in the USA they use a lot of stuff in our gasolines.
There are all sorts of things that can vaporize and make bubbles.
A typical pump gas MSDS sheet says they have stuff like this in the fuel:

COMPONENTS CAS NUMBER AMOUNT
Gasoline 86290-81-5 100 %vol/vol
Benzene 71-43-2 0.1 - 4.9 %vol/vol
Toluene (methylbenzene) 108-88-3 1 - 25 %vol/vol
Ethyl benzene 100-41-4 0.1 - 3 %vol/vol
Xylene (contains o-, m-, & p- xylene isomers in
varying amounts)
1330-20-7 1 - 15 %vol/vol
Butane 106-97-8 1 - 12 %vol/vol
Heptane 142-82-5 1 - 4 %vol/vol
Hexane 110-54-3 1 - 5 %vol/vol
Cyclohexane 110-82-7 1 - 3 %vol/vol
Methylcyclohexane 108-87-2 1 - 2 %vol/vol
Pentane, 2,2,4-trimethyl- (Isooctane) 540-84-1 1 - 13 %vol/vol
Naphthalene 91-20-3 0.1 - 2 %vol/vol
Ethanol 64-17-5 0 - 10 %vol/vol
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Old Dec 15, 2012, 11:27 AM
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Bert, I was only referring to your remark that I quoted...

Regarding bubbles; we are repeatedly being told to isolate the fuel-tank from the air-frame, to prevent "the fuel from being churned into foam by the engine's vibration".

This is utter nonsense!

Take any fuel and vibrate it, stir it, blend it any way you want and by any means...It will never form any foam/froth/lather that is rigid enough to hold the clunk above the liquid fuel.

In F3A planes and other racing aircraft, that vibrate like the dickens with their 30K RPM engines, the bladder type fuel-tank is not isolated at all; and 'fuel foaming problems' are still nonexistent.

The problem with vibrations, is that they can cause all the walls of the fuel-tank to reverberate and to deflect the clunk all over the place, including into the air where no liquid fuel resides; resulting in the clunk 'gulping' air that appears as bubbles in the fuel-line.
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Old Dec 15, 2012, 12:04 PM
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earlwb and brutus,
I hope I don't need to open up the pump/regulator since I have never done it, and luckily the bubble issue seemed to be resolved pretty well with the pump being isolated properly. but if I need to open up the pump/regulator to service it, your directions will be very helpful.
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Old Dec 15, 2012, 12:05 PM
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do you guys have any idea of the higher RPM problem that I am facing? is it just the way it is during the break in process of this particular engine or something else?
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Old Dec 15, 2012, 12:22 PM
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Originally Posted by DarZeelon View Post
Bert, I was only referring to your remark that I quoted...

Regarding bubbles; we are repeatedly being told to isolate the fuel-tank from the air-frame, to prevent "the fuel from being churned into foam by the engine's vibration".

This is utter nonsense!

Take any fuel and vibrate it, stir it, blend it any way you want and by any means...It will never form any foam/froth/lather that is rigid enough to hold the clunk above the liquid fuel.

In F3A planes and other racing aircraft, that vibrate like the dickens with their 30K RPM engines, the bladder type fuel-tank is not isolated at all; and 'fuel foaming problems' are still nonexistent.

The problem with vibrations, is that they can cause all the walls of the fuel-tank to reverberate and to deflect the clunk all over the place, including into the air where no liquid fuel resides; resulting in the clunk 'gulping' air that appears as bubbles in the fuel-line.
Actually, it is not.... I had a SkyFox Cub helicopter, that would always start to run irregular at half tank level, with bubbles in the fuel line. Not with full tank, not with almost empty tank, ONLY at half tank.
Hovering with the canopy off showed the tank getting "critical" at half level, creating lots of movement. but the clunk stayed at the bottom (I do not have that video, but it is video-confirmed)
Fitting a Felt-clunk cured the problem: the tank would still shake and foam, but the felt-clunk prevented the bubbles fom entering the line.
I use that on all my helicopters now and they all typically run untill the tank is literally dry....

Brgds, Bert
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Old Dec 15, 2012, 01:32 PM
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kentli can you please re-explain your high speed engine issue you are talking about? I wasn't sure about what you had stated earlier in light of the more recent events.

Yeah I was going to mention an anti-bubble clunk, but I had forgotten it. Thanks for mentioning it Bert. They work in certain cases like Bert had.
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Old Dec 15, 2012, 01:52 PM
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the high rpm problem seems to smooth out as I'm breaking it in and at the same time riches the needles more. currently LSN 7 out, HSN 3 out. now at around 7000rpm, it will rapidly increase then soon die, like if it is really lean near the top, but needles already opened out so many turns already...
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