Turk1, I was thinking that it may not be vibration so much as heat. The ambient temperature was around 90 degrees Farenheit or 32 degrees Celsius. Then with the fuel pump absorbing heat from the engine as it does get quite hot sitting right behind the engine, the gasoline would turn into vapor. It would be getting close to having a classic vapor lock situation like you can have with a car engine in some cases. When the fuel is going through the pump, the fuel is going from a higher pressure zone to a lower pressure zone and it gives it a chance to turn into a vapor. Next weekend, I'll experiment with a heat shield to see what happens. But it looks more and more where one keeps the fuel pump in a location where it doesn't get heat from the engine. OS had a similar problem with a remote needle valve assembly that was contained inside of a backplate on a engine. It would heat up and cause the fuel to generate bubbles too.


Brace, I had the same problem trying to start the engine. It would flood out at low throttle on me. So I had to close the main needle, get the engine to start and run like that and then before it died, open the main needle a couple of clicks. The low speed needle was way off and needed to go in around two turns or more before I could get away from it flooding out at low speed. On my engine the low speed is almost set, but I ran out of time tweaking it yesterday. So next weekend I ought to have it dialed in.


Here is a short video clip showing the bubbles in the fuel line that was occurring when the fuel pump was mounted behind the engine. So vibrations might be the problem but I think it was the gasoline turning into vapor inside of the fuel pump due to the heat it was picking up. My other videos of the engine running Ok didn't turn out I'll have to re-do them. The camera got a oil drop on the lense and it smudged all the videos and pics after it happened.

NGH 9cc gasoline engine fuel pump getting bubbles in the fuel line during engine test run (0 min 18 sec)

Mine is on the way.Before bench mount,I will disintegrate the pump and check for any of malfunction cause.Imo, without suction by engine,pump should not let fuel go.
Earl,after several run of your engine if you reopen your low speed needle do you think engine will be flooded again?

I almost have the low speed needle set now. It was way out of adjustment, I wound up with it going in several turns before the flooding out at low speed would stop.

The trick I used at first was to close the main needle, open the throttle to about 1/8 open, then start the engine, when the engine ran off the excess fuel, it would catch and start running. I then quickly opened the main needle about two clicks. Then I could advance the throttle a little and open the main needle a little more. Repeating as needed. Then I would go back to low throttle and adjust the low speed in farther and farther. The engine would usually flood out at first, but it kept getting less and less as I adjusted the low speed needle. So now it is pretty close to being adjusted OK. Once I get it working OK, I can then close the throttle and count the number of turns "in" for the low speed, to have a idea as to where to set it for the next time I need to do it.

do you have two different fuel pumps ?

Yes I have two fuel pumps, they both did the same thing too. I bought a spare just in case.
When the first pump exhibited bubbles in the fuel line, I then tried the second fuel pump and it did the same thing.
When I went to remove it I noticed it was quite warm or hot to the touch. That was when I had the thought that the gas was vaporizing inside the fuel pump. So I unbolted it and let it hang loose below the engine. Then everything started working well for me then. I tried the first pump again and it worked fine like that too.

Could use a plastic isolator block like they use on the chainsaws that is to prevent vapour lock. It's a wonder there isn't vapour lock in the carb the way it's bolted to the engine solid, although it may run cool enough not to be a problem. Just thinking out loud.

Gord.

Still problems with firing in fact not even a hiccup, what is the best method to check the ignition?
Never mind, brain is going in circles with frustration.
I wonder how the hell they got this to run in the factory?
Going to burn out my starter motor at this rate

From the sounds of it, the motor is easy to flood, so two things. Pull the fuel hose off the carb first so it won't pump fuel into the engine and put a plug in it. Make sure the ign is shut off. Take the spark plug out and put a rag over the spark plug hole because it may spray gas all over the place. First off is the plug wet with gas? If so, bang it on your hand and blow it out so it looks reasonably dry. Ceramic inside should be white if it's never run. Now, wind the motor over with you starter and see if it sprays out fuel. If so, wind it over till no more comes out. This is where you want to make sure that ign is off as this is a very volatile mixture coming out of there. Now turn on the ign and ground the plug base to the motor to ground it. You can use alligator clips if you like. Now turn the motor over to see if you have a spark. Go this far and let us know the results.

Gord.

What I did to check the ignition was with the spark plug loose and plugged into the cable and power to the ignition system, I held the sparkplug down against the non-anodized part of the engine, and flipped the prop over so that the magnet goes past the sensor pickup. You should see a tiny spark, if it is working. Do be careful with the spark plug it is easy to accidentally close the gap on it, it also can be broken easily too. Do not try to draw a long spark, it causes the tiny wire windings in the ignition coil to short out, from the excessive high voltages involved.

If the engine is flooded it can drown out the spark plug enough to have a bad spark, sort of a short circuit.

Like flypaper2 stated you can unplug the fuel line and spin the engine to help flush out the excess. Do disconnect the power to the ignition system first though. Removing the spark plug helps too and drying it out some as well. Then what I did was close the main needle valve. Then with everything hooked up I spun the engine until it caught ran ran a few seconds. Then that got me close enough to find that the now speed needle was way out too far and needed to go in several turns.

Originally Posted by flypaper 2

Could use a plastic isolator block like they use on the chainsaws that is to prevent vapour lock. It's a wonder there isn't vapour lock in the carb the way it's bolted to the engine solid, although it may run cool enough not to be a problem. Just thinking out loud.

Gord.

Glow engines use methanol which is a good coolant for the engine. The carbs can actually ice up from the cooling effect, so they need some heat to work better.
The gasoline carbs have a small cooling effect from the gasoline too, but not as much as methanol provides.

From Wikipedia:

In hot weather, excessive volatility results in what is known as "vapor lock", where combustion fails to occur, because the liquid fuel has changed to a gaseous fuel in the fuel lines, rendering the fuel pump ineffective and starving the engine of fuel. This effect mainly applies to camshaft-driven (engine mounted) fuel pumps which lack a fuel return line. Vehicles with fuel injection require the fuel to be pressurized, to within a set range. Because camshaft speed is nearly zero before the engine is started, an electric pump is used. It is located in the fuel tank so the fuel may also cool the high-pressure pump. Pressure regulation is achieved by returning unused fuel to the tank. Therefore, vapor lock is almost never a problem in a vehicle with fuel injection.

The EPA has this info about gasoline vapor pressure (which is variable due to the different blends and stuff they use)
The U.S. Environmental Protection Agency's publication "AP-42: Compilation of Air Pollution Emission Factors", Chapter 7, Table 7.1-2, publishes the True vapor pressures (in psia) at 40, 50, 60, 70, 80, 90 and 100 deg F for gasolines having Reid Vapor Pressures of 7, 7.8, 8.3, 10, 11.5, 13, 13.5 and 15.

Since it was 90 degrees F ambient temperature outside when I was running the engine, and the engine heated up the fuel pump even more, I needed at least 13 psi pressure to keep the gasoline liquid instead of forming gas bubbles. Which in our RC environment would not be practical.

Anyway my theory so far is the gasoline was turning into a gas inside the fuel pump in the tubing going to the engine's carb. The carb is drawing fuel still so there is a slight low pressure region in that fuel line between the carb and the fuel pump. Ideal conditions to allow gasoline to vaporize.

I would bet that in China a lot of their engine testing was done in cooler or even cold weather when they were developing the engine design.

Brace, I actually had the engine running at full throttle Ok with the low speed way out of adjustment, so I can see the engine testers in China not having a problem test running the engines there. I haven't figured out how to explain how one goes about doing it yet. I am still trying to figure that out for explanation myself.

Thanks flypaper and earlwb, went through the checklist and have got the engine running Very rough at present as the needle settings are set fine for full throttle as you mentioned earl.
Brought the cylinder head up to temp and then stopped it for a full cool down. In another hour I will run it again and see if I can get the little beast to idle better. Probably take a several run ups to seat everything in and make tuning easier.
not as noisy as I thought it might be.
All good here, love to hear some ideas on tuning.
Glenn

Hmm bubbles between pump and carb with poor idle when brought up to temp, lots of oil out the exhaust port. When low speed screw is turned in to lean out? engine stops. Presently 3 1/2 turns out with the Low speed. High speed is at 3/4 turn out.

So Earlwb, are you thinking of fitting the pump on a rubber mount separate of the engine say on the firewall or the engine mount? 8cm being the max length for the fuel line from the pump to the carb could be difficult.

I am still thinking about what I'll do for that.

Originally Posted by earlwb

I would bet that in China a lot of their engine testing was done in cooler or even cold weather when they were developing the engine design.

I think they are moving the factory to southern China where the weather is warmer...