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Old Feb 04, 2012, 06:34 PM
Complete RC Idiot Savant
The Netherlands
Joined Nov 2009
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Just to make sure: try a felt-clunk to eliminate any bubbles in the fuel caused by vibrations.
Pump carburettors are very sensitive to any bubbles in the fuel: Airbubbles change compressability of the liquid and thus hinder the pumping action the movement of the membrane is ony very small so the slightest air in the fuel is causing trouble.

Of course, when the membrane is leaking, that is not going to help, but at least then you know that the bubbles are definitely not coming from the tank.

Brgds, bert
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Old Feb 05, 2012, 12:08 AM
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gravityking's Avatar
United States, CA, Woodland
Joined Jan 2012
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Quote:
Originally Posted by flavinn View Post
do you think the air is coming from where? thanks
Ripped diaphragm, warped casting, I'm not sure. Had plenty of fuel. Will do pressure tests on tank & line integrity first.
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Old Feb 05, 2012, 12:09 AM
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Hervey Bay, Queensland, Australia
Joined Mar 2008
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Gents

Ran engine with Meteor twin needle carb. Carb spigot, originally 15 mm in diameter, was turned down on a lathe to 13.95 mm diameter to fit engine.

Top end easily set. Bottom end required much winding in of LS needle, but also was easy to set.

As expected transition was poor. HS needle is too blunt, it needs a finer taper. It will be removed from carb for re-profiling and further testing.

Engine started readily. Some perseverence will be required. However I am confident of achieving a successful set up.
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Last edited by fiery; Apr 07, 2012 at 05:48 AM.
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Old Feb 05, 2012, 04:39 AM
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I was using two hoses and two nozzles at the ends of weight, I think they were beating each other. pulled a hose and put foam under the tank, I'll try to test today. This can slow the bubbles??
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Old Feb 05, 2012, 05:26 AM
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Kingston, Canada
Joined Jun 2004
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Try blocking the tank vent line. Fill the tank and blow on the tank outlet with the tank full of fuel. It should show where the air is coming from.
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Old Feb 05, 2012, 06:51 AM
Complete RC Idiot Savant
The Netherlands
Joined Nov 2009
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Quote:
Originally Posted by flavinn View Post
I was using two hoses and two nozzles at the ends of weight, I think they were beating each other. pulled a hose and put foam under the tank, I'll try to test today. This can slow the bubbles??
If you are wondering if the bubbles are caused by vibrations, I repeat: try a Felt-Clunk first. It will eliminate ALL air that might be mixed with the fuel due to vibrations entering the suction line.
If you still have air bubbles in the line with a felt-clunk installed, you know that there is either a leak, or a ruptured membrane or something similar.

Felt-Clunk is anyhow a recommended item, as they simultaneously are the best fuel filters availlable, better than anything else. And next to air bubbles, impurities are the next thing a pumpcarburettor really hates....

Brgds, Bert
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Old Feb 05, 2012, 07:25 AM
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someone has managed to fly with this engine?? so far we have only seen on test bench
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Old Feb 05, 2012, 10:38 AM
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I smell another crap engine like the other NGH and JBA engines, all them designed by the same person. what did you expect ?
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Old Feb 06, 2012, 12:23 AM
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I'm drawing from a gallon fuel can on an isolated surface from the stand so aside from a leaky connection I shouldn't have bubbles.

Used a MightyVac on the supply line to the pump and no loss.

Pulled the cover off of the crankcase pressure side of the pump and it was damp. Could have been oil from crankcase so inconclusive.

Really anxious to see how Havoc makes out with a Perry.
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Old Feb 06, 2012, 05:39 AM
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Plus 1 with Doctor X.
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Old Feb 06, 2012, 07:30 AM
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video of the flight - still needs adjustments
Motor NGH 9cc - modelo stick 40 Aeroparque Anápolis.Go.wmv (2 min 14 sec)


Voo com NGH 9cc - modelo Stick 40 (2 min 48 sec)
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Old Feb 10, 2012, 02:52 AM
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Canada, MB, Winnipeg
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The engine fine the fuel system sucks

I've worked on hundreds of engines from weed wackers to IHRA prostock engines and you can't have a carb with a constant supply of pressurized fuel without some way to control the flow. To match the output of the fuel pump to the engineís need is almost impossible and just using a needle valve isnít going to cut it. In this case the carb is actually working more like a throttle body on a fuel injected motor. The engine should be drawing unpressurized fuel from the carb. I know with my old O.S engine they offered a venturi adapter if one did not want to use exhaust to pressurize the fuel tank.

A 2 stroke glow engine does not behave the same way a 2 stroke gas/oil engine does. The alcohol in the glow engine fuel actually provides some oxygen when it burns and alcohol engines can run rich; the gas/oil engines can not. Also donít forget how the glow plug actually works. The glow engine also uses the exhaust to pressurize the fuel tank and we set the high speed adjustment to compensate. The gas/oil engine uses a vacuum/pressure pulse to work the pump. If the ring/s seal better then there will be a better vacuum/pressure pulse and the pump will work even better.

The diaphragm assembly on the carb shows that they attempted to use a setup similar to a Walbro or Tillotson setup with a diaphragm, needle and seat, please see my attachment. In the picture youíll see at the bottom (red area) the fuel is actually under a slight vacuum because fuel is being drawn into the engine. On the left side coming down is pressurized fuel to the needle and seat. The setup works similar to a float with a needle and seat except there is no float. On one end of a rocker arm you have the needle an on the other you have a spring and a diaphragm. The pressurized fuel will force the needle down and the spring will try to force the needle up. The diaphragm will work against the spring and will help keep the needle off its seat. As the chamber fills with pressurized fuel the fuel pressure will push the diaphragm down. When the diaphragm goes down it allows the spring to force the needle up and stop the fuel flow. The fuel in the chamber will only be pressurized for a short time because the fuel will be drawn out and a new balance level will be created with the fuel in the chamber under slight vacuum. I hope this explains the problem with the NGH fuel system.

I have not seen the inside of the fuel pump but would love to if someone can post some pictures. So what can be done with this NGH fuel system? Well I think that NGH should replace all the carbs with ones that are designed and finished properly. In the short term the fuel pressure and volume need to be controlled better.
Things I have done in the past:
- put an orifice in the crankcase pulse line or even an aquarium air control valve (the brass ones with fine adjust)
- Change the system from a returnless to a return type by using a ĎTí in the fuel line going to the carb and put a brass fine adjust valve like the one used above on the return line past/after the ĎTí and carb and then run the line back to the tank.

Remember you only need 1psi for this to work but 1-3 psi will do.

As for bubbles in the fuel supply line from the tank, it is most likely a pin hole or a crack in the pump diaphragm. The diaphragms usually crack along the outer edge close to the case. Pull the line from the crankcase, suck on it and plug with your tongue, the vacuum should hold for a least a minute.

Ray
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Old Feb 10, 2012, 03:05 AM
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I also agree a return line just before fuel nipple of carb. to tank will be better than absolute fuel supply.
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Old Feb 10, 2012, 10:17 AM
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Canada, MB, Winnipeg
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Quote:
Originally Posted by turk1 View Post
I also agree a return line just before fuel nipple of carb. to tank will be better than absolute fuel supply.
Actually you want the 'T' right at the carb nipple and the valve on the return line between the carb and tank, use the fill line nipple on the tank for the return. The right angle fitting on the 'T' goes to the carb.

Ray

P.S. This works great on my racecar.
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Old Feb 10, 2012, 03:58 PM
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Quote:
Originally Posted by turk1 View Post
I also agree a return line just before fuel nipple of carb. to tank will be better than absolute fuel supply.
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