RE: NGH 9cc Gasoline Engine
It was a hassle at first as I wasn't used to running a gasoline engine at the time.
But the efforts of several other people and myself came up with this list of things to do or check.
1. The motor is not a plug and play from the box, you will need to do some work and buy some more items.
2. First is I would take off the back plate of the motor and replace the threaded pressure nipple with a larger one. 8/32 fitting from Dubro seems to be the popular one and this will require drilling and re-tapping. I also replaced the pump fuel fitting with a larger 8/32 fitting too.
3. The pump/regulator should really be pulled apart and serviced with a Walbro K20-WAT kit, this will replace the diaphragms, gaskets, metering lever and plunger needle. I would also have a look at the faces of the unit where the gaskets seal on and see if they are smooth. If not then smooth them off by putting some cutting paste on a sheet of glass and run the face over it in a gentle figure eight motion to bring the surface smooth and level. I used a fine stone at first and while this worked it created a slight curve in the face which I later had to remove. The new gasket and diaphragm will handle the newer fuels and not get out of shape quickly. I like using the white Teflon pump diaphragm but trhe blue diaphragm works fairly well too. The Black diapghragm also works good in comparison to the OEM rubber parts. You may be able to forgo the smoothing operation, it depends on how well the pump/regulator works for you and how much it leaks or seeps when the engine is running.
4. If you are really into servicing the pump/regulator then you can also replace the metering spring with a Walbro WYJ 98-3160-7. The spring is a little more short and increases the fuel pressure to the engine. If you mount the pump/regulator really close to the engine, you may not needed it though.
5.Some people have used 1/8th Viton tubing for the pulse line to minimise loss of pulse to the pump/regulator. I have seen some use a brass tube with tygon at each end to do the same thing, not a bad idea but you would want the tubing to be barbed. I had good luck just using 1/8 inch Tygon tubing though.
6. When putting the motor on the test stand, or plane, have the pump/regulator on some sort of foam mount to absorb vibration. It has to be positioned as close as you can to the carb, allowing for the exhaust pipe, 80mm is the recommended maximum distance.
7. Fuel tank can be where ever you find space and height is not an issue.
8. When fitting the prop, be sure the collar which has the earth magnet for the hall sensor is in the correct position. It can be rotated and fitted back in place 180 degrees out. I am sure all of us have made the mistake but it is easy to check, rotate engine until tdc and sensor will be near the magnet.
9. Make sure all your fuel connections are air tight and secure.
10. Fuel mix is 20:1 don’t even think about 25:1. I also use a really good oil such as Amsoil Saber Pro 100:1 or Stihl Ultra oils in my engines.
11. Without the new spring on the pump/regulator my needle settings are LSN a touch more than 2 1/2 HSN just under 1. When you first start it I would put the LSN at 3 and the HSN at 1 ½. Depending on your mods, the standard LSN needle setting is six turns out and the high speed is 1 and half turns out. Idle is typically 1/2 open of the carb. But with the mods you may have it closer to being closed though.
12. Be sure you are only supplying the correct voltage to the ignition unit 4.8v. The CDI using is rated for 6.0v maximum and they really mean it. A five cell Nicad or NMH pack exceeds 6.0v when fully charged as do LiPo packs or LiFe packs. Anyway a 4 cell 4.8v battery pack works quite well any extra voltage won't gain anything at all.
13. Before starting with the ignition off rock the prop back and forth to pump fuel up to the carb. Start the motor with about ¼ of the barrel open. If it does not start straight away you may need to open it more to get more air into the motor. Starter motor required.
14. Adjust your needles to best setting. I have so far with an engine that is still running in, achieved 2500 to 10500 rpm with a 10.5x6 APC prop
15. Motor runs nicely but does sputter a bit and definitely spits fuel out as the carb is very basic and only just does the job. Work in progress with improving the performance.
16. Some people had problems trying to run it inverted and that may be the carburetor design. So it doesn't like that so far.
On my engines I wound up with idle speed being with the carb barrel about 1/2 open. So your results could vary on that.
The OEM rubber diaphragms in the pump/regulator may work much better using gasolines outside of the USA.Here in the USA they use ethanol in the fuel along with a number of other unpronounceable chemicals too. Here in the USA the SEF or Tru-Fuel premix gasolines don't deteriorate the rubber parts as fast and it may not need replacing then. The Chinese didn't have our USA gasolines to use in the engines so they wouldn't have likely encountered the problem. With USA pump gasoline the rubber parts get soft and stretch out and thus quit working on one.