Detlef Kunkel

[QUOTE=Jaketab;12696356]FYI. Just to confirm my suspicion about why the APS Pump failed. I reattached the collet to the motor shaft with some JB Weld. Plumbed up to some smoke oil to test. The pump worked as it should.
I will not be reusing this pump because it has been unsealed, the JB won't hold over the long term, and I don't like the idea of loosing an expensive aircraft.
It would be interesting to know if anyone has had a pump failure. This is the only incident I can recall from this thread.
Thanks all,
J Tab



Jake,

OK so far, but still no sign why the pump ran hot? No sign of blocking, damage on some gear or debries?

If its not the Motor, the fitting of the gears inside their housing, it must have been some dirt particle that had managed to enter the pump to make it turn so hard?!

Jaketab

My Feedback: (2)

Detlef, I agree. Gears turn freely. The manual does caution that the pump could fail if run dry even for short period.
"Used pump for sale. Warranty expired. Only disassembled once. Missing one small ball bearing part. Marked down to $100 USD." LOL

Detlef Kunkel

Now that was THIS pump?

Jaketab

My Feedback: (2)

Yes, sorry, just a bit of humor. The old pump should be considered junk.

JJP

My Feedback: (1)

Non related but I need to clean up the threads on one of my spark plug holes. Can anyone tell me the tap size for the moki 250?

Detlef Kunkel

M10x1

Be careful to avoid dirt particles falling into the cylinder

mitchilito

My Feedback: (7)

I just caught up on the last many posts regarding carbs, pumps etc. FIRST I wanted to chime in and say I'm just thankful we Moki owners have this invaluable resource to refer to for the proper running of these marvelous engines. Second, it became clear that there are only a couple of fail points that keep affirming themselves. They are as follows:

1) Moki air pump pulse line clogged with grease.
2) Electric fuel pump failure, (mechanical or electrical)
3) Walbro regulator section leaking

If you go back and review every fail post it's probably going to be one of these three things, so start troubleshooting there.

Detlef Kunkel

Mitch,

to complete your list, sometimes ignition and / or the pickup sensor fail and stop a nice flight before the planned ETA

We corvered already the big round metal connector plug to come loose if not secured

Captainbob

My Feedback: (4)

[QUOTE=Jaketab;12696565]Detlef, I agree. Gears turn freely. The manual does caution that the pump could fail if run dry even for short period.
"Used pump for sale. Warranty expired. Only disassembled once. Missing one small ball bearing part. Marked down to $100 USD." LOL[/QUOTE
Why is everyone spending the exorbitant sum of 250.00 for a fuel pump when Magom offers several, high quality, brushless, gear pumps for under 100.00....??? If you're locked into a cheap brushed one like Moki recommends, Magom has one for about 60.00.

Captainbob

My Feedback: (4)

Detlef,
Your critiques on the Moki failures are right on. So why not try something different
Use a carburetor with a more appropriate throat area. A smaller throat increases induction gas flow. This reduces static press. In the throat making fuel draw stronger. No pump needed and, now, high-speed needle is more effective at richening mixture.

Robert-H

I also want to complete your list and that is the lower cylinder temperature, if not carefully monitored during warm ut I may be filled with fuel/ oil and will not fire up properly
Main problem is gravity, but it can be handled quite well, avoiding to much idling on ground and a to rich carb setting, also a temp gauge on each cylinder gives you a good indication if the engine id ready for takeoff

Also regarding pont 1. I think the black grease (from cam lubrication) is a sign that the little piston is worn out, allowing grease to enter the air-pulse chamber, and its time to put in a new one.
I discovered during my build of a electric air pulse pump, using the same dimensions as Moki, how sensitive the piston gap in its cylinder bore, is for making a powerful pulse, the 10 mm cylinder needs a max gap of 0,04mm if it gets up to 0,08mm, half of the pulse energy is lost

Jaketab

My Feedback: (2)

Captainbob - With respect to your idea to a smaller carb bore diameter, could the answer be as simple as adding a velocity stack with a plate to restrict and speed up the air-flow ??? Both of my Moki 250's have V stacks and run very well at idle and top end rpm's. The high and low needles are optimized. However, both have a midrange somewhat not as smooth. (Nature of the beast) As mentioned, I believe this is typical for the Walbro at the mid rpm range where both needles transition and influence the fuel flow too rich.
I don't recall it's name, but there was a device sold some years back that had an impellor that would speed up the velocity of air entering the carb with the theory of making a more atomized fuel mixture ???
Thanks - J Tab

Maxam

My Feedback: (62)

J Tab, Sounds like you are referring to the Detlef Kunkel turbulator that installs between the engine and the carb. I have both of my 215's with this device. Its purpose is to make equal distribution of the fuel mixture to all the cylinders. The spiral vanes are adjusted by 5 degree rotations between runs until all five cylinders are within 5 to 10 degrees Fahrenheit of each other. Lot of work but I have two sweet running 215's. It seems this device is not needed on the 257 due to equal distribution of fuel on this model. -Tom

tziger

Hello all,

i have purchased a Moki 180 last year. I tried to run just 2 tanks on a bench and then - because i read that i should just put it on the plane and fly - i installed it on a very expensive and work intensive model i have been building for the last 5 years.
Let me say at this point that i am not someone who starts complaining immediately and i thought that i should not be dragged into all the issues i have read for mokis on this thread .
BUT, the motor is a pain to start. It seems that it does not bring enough fuel to the cylinders. I have spent a full day with a friend tying to start it on the plane. Finally it did by our right arms needed couple of days to recover.
Of course i did not fly. I do not feel at all comfortable to fly with an engine that starts whenever it wants. And the damn thing is brand new.

By talking to some people who have mokis they advised me to run in the motor on a bench for at least 10 hours. Fine, i said let's do this.

I installed the motor on a bench:
1) First day on the bench: The motor started relatively easy. The issue was that i could not increase the throttle more than 3.000rpm since the engine would reduce revs to the point of stopping. I burned 1lt at this state.
2) Second day: The motor started easily, again could not increase revs and started to be worse and worse. I burned another tank.I stopped for the day since i could not get it started after the tank was done. I checked the valves in the night and readjusted them since the motor has run for about 3 hours.
3) 3rd day on the bench. The motor would not start. It would burb when on choke but afterwards it would just be dry from fuel after 3-4seconds. By looking i realized that the small festo tube was black from grease near the pump. I said that's it. I cleaned the small festo tube and the motor started easily. After though couple of minutes of running it started again to be dry from fuel and i could not increase the throttle. Again black grease in the tube. That seemed too fast according to what i have read n this thread. At the same time i realized that the fitting of the festo tube was loose. I tightened the fitting, cleaned the tube again and started the engine. Now it run nicely, it increased revs to full throttle. For about 10 minutes.
After that again no full throttle, and now it does not start again. When i choke it turns but it stops after couple of seconds.
But now the fittings are tighten and the tube is clean so , i am out of ideas. Can anyone please help?

I am really frustrated with the situation. I appreciate any help.

Lawrence.

avio-nico

Lawrence, did you check the spark plugs an the ignition?

Quality of the spark for each one, cable connector/connections, status of battery etc?

Did you try to open the top of the carburettor checking for grease or debris?
Did you check the carburettor diaphragm for function and integrity?

GeorgiaFlyer

I agree with all the items Avio-Nico suggested. But I would also suggest that you use an electric fuel pump with these Mokis and not rely on the pulse pump. I have three Mokis all with fuel pumps and never had an issue with starting or running the motors. I know others have had success with the pulse pump. But if you are having these issues right out of the gate with a new motor, I would go ahead and get a fuel pump. I really believe you will be happy. Once you get these motors worked out with the initial kinks they really do run well.

Maxam

My Feedback: (62)

I read carefully that there was no mention of attempting to open up the carb H and L adjustments. Try an eighth to quarter turn open on the H needle. It is important to understand, the H affects the L and vice versa. If the L needle is in too far the engine is typically difficult to start and will quit in the air. If the L needle is too rich the engine will be "blubbery" and run only on three or four cylinders in the lower to midrange throttle positions.

tziger

Hi all,
thanks for the fast replies. I am at home so i just took the motor out of the bench and took out the carb. The only thing i noticed was that the 2 green flanges on the carb extension were wet from fuel which could indicate that it did not seat well but i do not know for certain. I tighten everything back but did not find any thing revealing. No debris or grease. I did not take out the needles. Should i ?

I did played with the high and low. The differences were only with the low where if too lean the motor would increase RPM and further quit.

How do i check the diaphragm for function integrity?

I have not taken out the plugs because i am certain it is an issue of the carb. If the motor has fuel it runs normally.

Which exactly fuel pump should i buy if i decide to go this way?

Appreciate the feedback,
Lawrence

RichardGee

My Feedback: (156)

There is no mention of using an infrared temperature probe to CONFIRM if all cylinders are firing?
If Full throttle results in 3,000 rpm (assuming the engine is propped correctly), there is NO WAY all 5 cylinders are firing.
This could be the result of too lean or too rich - but mostly likely too rich as too lean would result in the engine stopping at full throttle.
Once the engine has been run too rich and a couple of plugs fouled, it is often very difficult to relight them.
The hard-starting is also most likely the result of the engine being too rich, with fouled plugs, and trying to start on less than 5 cylinders.
There is also no mention of confirming ignition battery voltage is adequate?
What oil and ratio is being used?

The engine should run PERFECT on the bench using the integral pulse pump, IF:

• Correctly propped
• Correct fuel/oil
• Carburetor is adjusted
• Ignition battery voltage is correct
• All ignition connections are good
• Plugs are not fouled

Until the engine can be made to run perfect on the bench, adding a fuel pump will merely create another variable and confuse matters more.
My $ 0.02

GeorgiaFlyer

This is the one I have used on all of my mokis https://www.aeroscale.shop/collectio...p-powerfuel-rx

tziger

Hi again,

I am running 1:40 for the first tanks. The oil is Motul 800 as per Airworld's instructions.
i am using an instrument with 2 probes secured on the engine. One on No1 and second on No3. In parallel i have an infrared to check the rest cylinders. The highest temp i have seen is 115Celcius on No1. The No3 is running always low although it has improved varying between 55 and 85Celcius.
The ignition batteries are brand new and i changed them yesterday to check if this was the issue. They are 2 parallel 3500Amps 2 cell Hacker. This means i have 7,5 Amps which is plenty of power.
I took out the plugs just now. They are all wet as expected since i was trying to start the engine.
Any remarks are welcome. One thing though, when i have difficulties to start i always go back to the factory setting of the needles, L 1 1/8 and H 1 1/4. If Low is less than 3/4 the engine was running higher RPMs and No3 firing better but it did not start when stopped.

RichardGee

My Feedback: (156)

No. 3 @ 55 celsius = NOT running
No. 3 @ 85 celsius = running INTERMITTENTLY

Trying to start the engine on 4 cylinders can be VERY difficult. Believe me... I know

ALL cylinders should be at least 100 celsius at full throttle, OR they are NOT firing consistently.

Your oil and mixture are OK. Plugs are wet and/or black, indicating there is PLENTY of fuel and oil getting to the engine, at least at lower throttle settings. #3 is clean, indicating it is NOT firing.

For now, STAY with factory needle settings. The engine should run OK at these settings.

Prop?
Ignition battery?
Do you have a SWITCH between the battery and ignition?
Fuel tank and fuel lines all GOOD? No bubbles?

Jaketab

My Feedback: (2)

Tziger,
Sometimes is easy to overlook the simple fixes when dealing with our airplane engines.
If it's a carb problem, more than likely the needle, spring, and lever are out of proper adjustment from the factory.
If its dirt in the carb, try removing the needles and spraying WD-40 or something like directly into openings. A good blast of solvent my clear out a dirt particle.
I've also used WD-40 to prime a stubborn engine.
As for the plugs, I have better success in my Moki setting the gap to .020" inches or .51 mm.
In the #3 cylinder, I use an Iridium spark plug.
In a new Moki, #3 won't come up to temp until the low needle is leaned to the optimum setting. In both my Moki's with a fuel pump, the low needle is from 3/4 to 7/8 open.
My Moki's like to be started wet. If you flood the cylinders, easy to clear by tuning off the ignition, open throttle wide, flip a few times, and then go back to regular starting routine.
What prop do you have on the 180.? Too aggressive prop can cause the engine to bogg down.
And last, the engine can be overheated on the bench stand. Monitor you temps carefully.

Regards - J Tab

StuartMackay

Lawrence, check the following:

Is the choke flap FULLY closed when priming the engine?
You should see fuel in the carb mouth if it is sucking correctly.
Set both needles to 1 1/2 turns open.
When starting, I always use the following technique:
1 Choke closed and ignition on
2 turn over the engine until you feel an Ignition Bump from one of the cylinders.
3 open the choke flap
4 set the throttle just open
5 flick the prop and the engine will run.

If it doesnt then it might be a faulty or dirty carb, all the engines are test run at the factory, is there anything that you have done like removing the carb and the gaskets between the carb and motor have got misaligned when re-assembling?

Playing with the black pressure diaphragm will not affect the starting, it is purely there as an altitude pressure compensation system diaphragm for in flight mixture fine tuning..

Do check the transparent gasket on the pressure pump side of the carburettor (where the Festo fitting connects) for any grease contamination from the mechanical pump and that the D shaped non return flaps are flat and seated on the machined face of the carb. We have these start to curl away from the machined face and this can cause starting issue with the fuel not staying in the carb and returning to the tank.

Before you start buying external fuel pumps, you can pressurise you fuel tank with air using a bicycle pump to check if this helps before spending 250 Euro on an APS pump.

Hope this helps and do give Airworld a call if you cant get anywhere using my above recommendations.

tziger

Hello all,

thank you for the feedback.
I have some news but no solution.
The prop is the one airworld suggested when i bought the engine so i will not question it.
I took out the carb yesterday to see if there is something i could identify. I took out the side of the festo tubing to check for dirt or debris. Nothing, everything was clean,. The only thing i noticed is that the 2 green gaskets of the carb spacer were wet. Which in my view means that the carb takes air from the side. But not sure how i can verify this.I reinstalled the carb with loctite on the screws.
I unscrewed the needles. The seemed clean.
The choke flap seems to close fine by visually checking but also functionally since the engine tries to start but stops after few seconds which means that there is fuel coming to the carb when the chocke is closed.
I put it on the bench this morning and the same thing. Few turns when primed but does not continue.

Stuart Mackay, this is the exact starting process i use. Ignition on, close the choke, hold the prop with both hands and turn it. When i feel a push i flip with the choke closed and it burbs. Then i open the choke set the throttle just open and flip it. It starts for a few seconds and then stops.
Concerning the carb i did not do anything until yesterday when i took out the carb. I generally prefer going with what the manufacturer suggests. That's why i have the prop airworld suggested, the oil and the air filter.
The engine was difficult to start from the beginning but at least when it run it was in the limits of what i read here. Now it does not start.

I tried with the 1 1/2 needles set but nothing changed.

I called airworld this morning. He agreed with me that this seems to be a carb issue. He asked me to send the engine back.
To summarize my story:
1) Difficult to start but run normally for 2 tanks.
2) After this it quits when full throttle.
3) High rpms got less and less.
4) Grease in the festo tube
5) Loose festo fitting at the air pump
6) Wet green gaskets of the carb spacer.
7) Everything back together and it starts when wet but stops after few seconds.

I will try to pressurize somehow the tank when i start it to see what happens.

I have a last question. How can i test if there is pressure coming from the small festo tube?

After that i will send it back to Airworld.

Again thank you all for the feedback. At least i do not feel alone with my new moki.

Thank you,
Lawrence