RCU Forums

RCU Forums (http://www.rcuniverse.com/forum/)
-   RC Warbirds and Warplanes (http://www.rcuniverse.com/forum/rc-warbirds-warplanes-200/)
-   -   MOKI RADIAL Care and Maintenence (http://www.rcuniverse.com/forum/rc-warbirds-warplanes-200/8946260-moki-radial-care-maintenence.html)

ram3500-RCU 01-06-2014 12:41 PM


Originally Posted by jairaksinen (Post 11702959)
It is the 120" version, but modified with hydraulic wing folding. I've also had the thought of repainting it to the Reno schemes, but we'll see.

Sounds really cool. Any pictures of the plane and what you have done to the Moki?

Might want to consider converting the wing to electric. Down & Locked can do it for you. He has converted many CARFs with no failures. That all but eliminates worries about loss of pressure, without the need for any redundant locking system.

jetpropdlx 01-20-2014 01:47 PM

Hello All,
Can somebody give me some hints and triks for troubleshooting a moki 215
During the last season I had several engine quits during flight
eg last weekend I flew two flights without any problem and on the third flight the engine stopt again.
Note: I almost never fly full throtlle , outside air temp. 9 degrees Celcius (42F)
My engine has the turbulator and fuel pump and there are baffels installed between the cylinders
The engine doesn't stop at once but ffirst looses power no reaction on the throttle commands (can't belief it was wind mailing ??) and after a short time the prop stopt.
After landing the fuelpump was running.
After bringing back the model back to its start position (everything tirned off), and tried to start the engine and it did.
Fuel tank was more then half full , as was the ignition/fuelpump battery.
The ignition kill switch is a powerbox killswitch

Thanks for any suggestion

ps now i am thinking , before I installed the baffles I didn't had any engine failure :confused: , could it be the ignition unit thats in the cowling behind the engine , is not getting enough cooling ???



ram3500-RCU 01-20-2014 02:16 PM

one to four is the ratio I try to get. That is four times the exit area to the inlet. I think she offs overheating on you from what you describe. if out had gotten hot, you may want to check the valve settings.

jetpropdlx 01-20-2014 02:56 PM

I installed those baflles (after half a year flying ) because the hot-air outlet is quit small and to make sure the engine is not over heating

nine o nine 01-20-2014 04:49 PM

Since the engine started and ran ok on the ground after an inflight failure with the tank about 1/2 full I'd suspect the fuel tank supply line. It may have either stiffend over time and is staying close to the 1/2 full position or it may have come off the outlet tube entirely. In the taildown startup position the fuel level angle might be feeding the engine. Just something else to check.
As Gary suggested to check the valve rocker clearances. An infa red heat sensing unit is a good way to check head temperature.Check running temps both with the cowl on and off and see if there's any difference worth noting. I have a Moki with a round cowl and air exits very similar to yours and cooling isn't an issue for me....no baffles on mine either. Mitch

Scale Specialties 01-20-2014 04:56 PM


Originally Posted by mick15 (Post 11702176)
I repeat one of my earlier posts to ask, “What is the preoccupation with pitch” why not use a larger diameter prop?
A ¼ scale warbird doing 125mph that’s 500mph, they’re not going that speed at Reno! They just look ridiculous. Remember, pitch is for speed, diameter is for weight.
I have a three blade 32x12 on my La7 and it’s easy to get that flying too fast.


when are people going to finally understand scale speed is not a linear relationship to scale?

Scale Specialties 01-20-2014 05:17 PM

Scale speeds for scale
1 Attachment(s)
Here is an excellent reference for "scale speeds" regarding models

Maxam 01-21-2014 04:13 AM

To Eric, The Ignition module must not be allowed to get hot. I have a feeling it gets real hot behind that baffling! Can you relocate the unit behind the firewall? A thought! -Tom

jetpropdlx 01-22-2014 03:41 PM

Thanks, For the tips
I just checked the rocker clearance
I did read some where in this thread the valve clearance should be between 0.05mm and 0.08mm (for both inlet and outlet valve) I had 0.20mm at most of them
Next week I wil try to adjust them, and look for a better place for the ignition unit
It's winter here , so it would be a few months before the Stagger will fly again,


kipuetz 01-28-2014 01:02 AM

Correct, 0.05 mm to 0.08 mm. NOT .005 to .008 "th of an inch!!!

Jaketab 01-28-2014 06:33 AM


In the beginning with my 250cc I was setting the rocker arm valve clearance gap too large. Upon learning the correct setting, I discovered the motor preformed much better and ran slightly cooler.
Therefore, the correct setting for me is the smallest amount of daylight (gap) without the rocker touching except when raised by the cam. With the smaller gap, the engine is less likely
to throw a pushrod.


Maxam 01-28-2014 07:08 AM

Like other radials with 2 or more cams on the track, check clearances, rotate the prop 2 turns and check again! The cam ring is not always perfectly concentric. Always better too loose than too tight. -Tom

reyn3545 01-28-2014 07:41 AM

And since we're turning wrenches around the cylinders already... does anyone know what the plug gap should be?

Pete Bergstrom 02-06-2014 12:35 PM


Originally Posted by reyn3545 (Post 11722270)
And since we're turning wrenches around the cylinders already... does anyone know what the plug gap should be?

.021 - .028" has been working the best for us.


reyn3545 02-06-2014 12:36 PM


bcrc 02-17-2014 09:54 AM

Possible solution to problem of cylinders #3 and #4 not running
Hello again. I have been following this thread since its beginning:
First a little history:
I have one of the first Moki 150 radials. I got it in the winter of ’08. This summer will be its 7[SUP]th[/SUP] season. The first few seasons I just flew it and was content. The only real problem was that in inverted flight and pulling upwards it seemed to sag and lose power unless I cut back to half throttle. Then on or about the 3[SUP]rd[/SUP] or 4[SUP]th[/SUP] season, I wanted to regrease the front end. When doing that I saw the “totally hokey” air pump and how it worked. That was about the time that Dr. Gotz started selling the electric pump for my Moki. I removed the air pump, installed the electric pump, and that has been working great ever since. Moki should be ashamed for selling these engines and not including a high-quality electric fuel pump. Then a few years ago, someone at the field told me that it sounded like a couple of my cylinders weren’t firing. Sure enough, a temperature gauge indicated that #3 was never running, and #4 only about half the time. This was about the same time that this thread was discussing the same problem. I waited a year or so, hoping that a fix would show up. Last summer, I decided to go all out to fix the problem. First we tried just fine tuning, tweaking, using the Denso plug, short gapping, etc. Nothing worked. We checked that all 5 coils were working – they were. Then I bought a Kunkel Turbulator. This didn’t help on the first try, but using the Turbulator and rotating the carb 180 degrees, we could get #4 to run almost all of the time, and #3 most of the time. But just when we thought we had it licked, the next flight #3 would be gone. We also tried the Rainbow ignition – it didn’t really seem to help. By the way, we also tried running the engine without the exhaust ring (just a shot). Nothing changed – just exhaust all over the place!
By now we were getting into winter and I had to shut down till next spring.

I am not going to give up. First a question:
In this thread several people have suggested that the problem is that, due to gravity, the lower cylinders get more fuel and thus a richer mixture. This would mean that if the engine were inverted, #1, #2, and #5 would go rich, and #3 and #4 would be leaner. I have seen some discussion about this on this thread – but, as far as I can remember, no one came up with definitive results --did anybody get a sure fix by inverting their engine?

My guess is that gravity isn’t the problem. I think it has to do with the shape of the carb and the paths to the intake tubes. Every cylinder has a different problem due to the shape/movement of the master rod and slave rods and the rotation of the crank in the back end of the engine where it is fed to the intake tubes. Of course this problem is not changeable. My hypothesis is this: We accept the fact that for a given carb setting, due to the design/shape/etc. of the engine, the #3 and #4 cylinders get a richer mixture than #1, #2, and #5. The only solution to this is to adjust the mixture to #3 and #4 so that they get a leaner mixture than the other three. This has to be done after the fuel goes through the carb and the bottom end of the engine, but before it enters the combustion chamber. I was running this by some friends of mine – some in the hobby, some out of the hobby (but good engine guys). One of them (who used to fly RC) came up with an idea that seems simple and might work. In fact it is so simple that it is scary! He suggested that we just add an air bleed to the intake tubes for cylinders #3 and #4 – just like simpler RC carbs back in the ‘70s used to use to adjust the idle mixture. It would seem that just drilling a small hole in the intake tubes (nearer to the carb and farther from the head) of #3 and #4 would add more air to the mixture and thus lean out the mixture to those cylinders. We could start with a small hole and increase it until those cylinders started running consistently. I am willing to try it this spring and see how it works. Has anyone else thought of this or, hopefully, tried it??

So, all you Moki guys out there – what do you think of this idea?

jairaksinen 02-17-2014 10:10 AM


Originally Posted by bcrc (Post 11738852)
So, all you Moki guys out there – what do you think of this idea?

I remember someone mentioned about the bleeder before on this thread. However, If you look at the intake channels, you'll probably see sharp corners and missaligned drillings. I fixed that on my Moki 250 and it instantly went lean, meaning better breathing of the engine. I did smoothing on all the intake channels which resulted in more torque and better throttle response (and more fuel consumption). Perhaps you could do only the #3 and #4 cylinders to get more air into them. But then if it really is issue with gravity, then you'll have issues when flying inverted. I have not tried my moki in the air yet, but in a few months the snow goes away...

PS. I suppose all of you moki lovers have noticed the new 300cc and 350cc coming this spring...

reyn3545 02-17-2014 10:16 AM

... edited.

Maxam 02-17-2014 11:34 AM

BCRC, I would not drill and install airbleeds in the intake manifolds. The amount of vacuum in the tube varies greatly at different throttle settings. What might give a good mixture at one setting will be a disaster at another. Also these holes will disturb greatly the mixture on other cylinders. I once put a collector ring on my UMS7-70. I forgot to tighten one of the intake manifolds. The air leak totally fouled up the whole engine. I, years ago bought a Moki 150 and yes it ran lousy due to the unevenness. I got the turbulator and it helped some as supplied. Are you aware you can fine tune it? The brass vanes are easily pressed out and can be rotated. A1/16th of a turn can have a great effect. I got my 150 dialed in well but not perfect. My 215 responded much more with all cylinders within 5-10 degrees of each other. I DID after fine tuning get the 150 to always run on all cylinders but there was a 25 degree or so spread in temps(not bad). I sold the 150 to a gentleman in Peoria and he has enjoyed the engine for about 4 years now. It may sound silly but rotating the turbulator and not the carb will have an effect. Get an infrared temp gun. Quite handy!

bcrc 02-17-2014 12:10 PM

Thanks for your response.
I have an infrared temp gun. That is now I determine whether or not a cylinder is running. I wasn't planning on installing airbleeds. A small hole itself would suffice as the air bleed. The material that the intake tube is made of is too fragile to install a needle-like air bleed. Drilling a small hole would just let air into that specific intake tube, and the air/fuel mix would always be being pulled towards the head, so I don't see how it would affect other cylinders - please explain. And, if it doesn't work, I'll just buy new intake tubes! I would probably just try it on #3 at first.

Maxam 02-17-2014 12:51 PM

If you put a hole in a given tube, the draw of that tube will be changed affecting the rest of the crankcase. It will be more pronounced at the lower throttle settings. The effect is the opposite of what you want in most cases. The hole will lean the idle position for the cylinder much greater than a mid to high throttle setting. The crankcase and all the intake tubes is one air space. The 150 intake tubes are "glued" in place with a sealer. You would have to break the seal, remove and drill the tube and then make sure when reinstalled to have a perfect seal again. Try the turbulator fine adjusting first!! I am well aware that it is a pain to take the carb off, rotate the stator, reinstall and run the engine then repeat. I did this about 4 times until I got a good running engine!

Jaketab 02-17-2014 03:46 PM


Consider that problems with #3 & #4 cylinders may or may not be related. Have you tried rotating the motor 180 degrees and measure the difference in cylinder temps ???
I would suggest that the internal ignition coils may be breaking down under heat, but I note that you have already tried the Rainbow ignition.
Are the valves not seating due to sticking or wear??? Early in the life of my 250, I had a gummed up exhaust valve in #4. I also had the #4 ignition coil to go bad.
Hope you can find the solution soon and post.


Maxam 02-19-2014 06:23 AM

It is my understanding that the 150 and 215 are no longer being manufactured. In my experience the very best running model is the 215 with the 250 just about as good. I wish I could afford another 215! I do feel fortunate to have one though. -Tom

GeorgiaFlyer 02-19-2014 08:09 AM

I bought a 180 new about three months ago. But only have run it on the test stand so far, plane is still on the build bench. The times I have run the 180 it seems to run pretty good. but it is new and still not broken in and like I said only run on the test stand. From what I have read the 180 does not need the tubulator and has had some mods to correct some of the issues with the earlier 150s. It also came with the newer ignition box (blue aluminum rectangular box). I did purchase a fuel pump but have not used it yet. My runs on the test stand have been without the electric fuel pump. I plan an testing again soon with it to see if there is any difference. Right now my plan is to use the electric pump once installed in the plane.

Maxam 02-19-2014 12:09 PM

Georgia Flier, Do all the cylinders have close to the same temp?? All firing? I sure hope so.

There has yet not any comment on the 7 cylinder engine! Does anybody have one?

All times are GMT -8. The time now is 09:38 AM.