In the thread "Oil Test Summary by rc bugman"
http://www.rcuniverse.com/forum/m_26..._4/key_/tm.htm

captinjohn mentions (post 81) that an oil manufactor recommeds shutting the engine down using choke. captinjohn took the step further and went to shut down on full throttle using the choke.

The procedure causes the engine to suck in a lot of fuel and oil. captinjohn describes easier starting even after storage, as he belives that the fuel/oil sucked in soaks the engine and loosening up deposits, that would otherwise settle.

No one really commented on this statements, what do you think?



As I sidenote, the manual for MVVS45 specifically says not to run the engine with the choke on:

"Caution!!! Never close the choke valve completely when the engine is operating! The choke valve is set to allow minimum air flow only when fully closed, which could cause damage to the intake reed valve."

Tor,

You might be able to get away with doing that on an engine like a Zenoah that feeds directly into an intake port. You will damage the reeds on that MVVS 45 if you try that method. Heed what the manufacturer tells you!

Most engines can be shut down by closing the throttle completely. Remove the idle adjustment screw and set the idle with servo end points then use your throttle trim or the "Throttle Cut" feature on your radio (if so equipped) and shut it down like you would a glow engine. I don't see the value of loading the engine up with unburned gasoline for storage, even if it does have some oil in it.

Bob

I agree with the method of shutting down an engine by reducing the fuel supply to less than the minimum necessary to run. If te idle is set correctly you should be able to completely shut off the fuel supply. From a personal standpoint I can see no valid reason for loading an engine up with as much fuel as possible in order to flood the engine.

The thought of having (even if it did indeed occur) a bunch of loose carbon deposits that had been disturbed by the flooding/shut down process floating around the top and bottom end the next time it started bothers me greatly.

Closing the choke is a reliable and quick way to kill the engine. Idle down, at least on my gas engines, will slowly kill the engine. When you cut the fuel supply you also cut the oil supply, and I’m not sure that’s a good idea. During flight I found that idle down would take quite a while to kill the engine. I never kill the engine at full throttle using the choke. That sounds like an accident waiting to happen. I have found that a choke servo will kill an engine as quick as an optical switch. It's your choice but I prefer the choke connected to a micro servo. It also works great for starting the engine.

Now Pat,,,, I always use the choke to kill my engine. As for the MVVS suggestion, I can't see how that would or could do any damage. In fact Pat (Silversurfer) hates chokes activated by servos. The first 2 or 3 times he flew my plane he actually missed the rate switch and killed my engine leading to dead sticks. He's good at landing with the engine dead

Should never use the choke to shutdown a reed valved engine.

RTK,

As you are fully aware, the only engines I EVER shut down with a choke are yours, and they will ALWAYS be in flight when it happens At least until you get rid of that G$$@$&** switch[:@]

The thoughts of a potential hydraulic lock due to the sudden application of the choke at rpm troubles me, though, so I use my trim lever to shut mine down. I've never had a problem with it shutting down slowly since I adjust my linkages and remove the idle stop screws on the carbs. Trim lever down, engine off. Pretty close to that quick.

Silversurfer is right, I've been using the closed throttle method for many years on all kinds of engines and never had a problem. Hydrolock or near hydrolock is a real risk when you choke it to stop.

I have done WOT choke kills and have not seen any signs of hydraulic lock yet, not that I try and do this on a regular basis though.

Shutting an engine down with the choke seems similar to using a servo to drop a rag into the prop. Sort of jury-rigged

Removing the ignition power or grounding in the case of magneto seems to be a much more positive and reliable method.

Bill

Ok, I have to ask the question. It has been stated that you should never kill a reed valve motor with the choke? Why should you not use the choke to kill a reed valved engine? Why specifically a reed valve engine?

One might guess that some will suggest that the bottom end will get full of gasoline and the reeds will check the release of pressure and on the engine down stroke the fuel will ignite like a diesel and blow the bottom end to smithereens thereby damaging the airplane. Ho, ho bang.

Bill

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You use a choke to start an engine don't you???? It fires then dies, right....

You are accomplishing the same thing when killing an engine at idle with a choke. It dies so quickly that there is no way of causing any problems.


Not even close

Not exactly elegant either.

Bill

Bill, you used a bad analogy,,,,
I was trying to make the point that dropping a rag on to a prop is no where near the same. That way people reading this thread will not get the wrong idea or think that you can not use a choke to stop an engine without damage. I have used this technique for many many years, on many engines without any damage what so ever.

Ralph

I agree that you can use the choke on SOME engines under certain conditions.

The original question was a bout an MVVS 45, a Reed valve engine, and shutting it down at WOT using the choke to suck gas into the engine. Not good for THAT engine!

Ok. So killing a reed valve motor by using the choke at WOT is the problem? It sounded as though people were saying "Don't use the choke to kill a reed valve motor." PERIOD. I myself have never seen or heard of anybody killing an engine at WOT. I currently run an Evolution 58GX and a 45GX .... and always use the choke to kill them ... AT IDLE. My thinking went along the same lines as Ralph. How can it damage anything when used at idle which is the same as using the choke to prime/start? As a matter of fact, both of my Evolutions start better at a fast idle so the engine rpm during that choke/start sequence is higher than when I use the choke to kill it.

BTW - My Evolution/Horizon manuals do not mention the warning that was quoted from the MVVS manual.

[link=http://h1071118.hobbyshopnow.com/ProdInfo/Files/EVO_45_58_manual.pdf]http://h1071118.hobbyshopnow.com/ProdInfo/Files/EVO_45_58_manual.pdf[/link]

MVVS does not prohibit stopping the engine with the choke. They just warn that opening the throttle with the choke on may damage the reeds. They are fragile.

There is no risk of flooding the engine into hydro lock. The largest load of crap I ever heard.
The jets are so small, that such a thing will never happen in the time needed to stop the engine, which by the way still is pumping and expelling gasses at the same time. It's the nature of the two stroke beast.
I find the engine easier to start if I used flooding to stop, or choke the engine well without the ignition on before I store the plane. At idle, the engine is slightly oil starved. The choking brings in extra fresh oil that conserves the engine. The extra gasoline carries the thinned oil in all nooks and crannies inside the engine by aerosol mist, and capillary action.

Another reason to use a choke servo over idle down is that it gives you a second way to kill the engine. If your throttle servo or linkage fails you have a way to stop the engine, like an optical kill. I actually had that happen to me three weeks ago when a HS-225 (trying to save weight) on my BME yak failed. Instead of flying around until it ran out of gas, I lined up to the run way killed the engine and landed. (I now have a 5925 on the throttle)

I don't know why you guys need to shut the engine off with the choke. I think a muck elegant idea is to cut the spark off. Look at the chain saws and weed eaters. That is the method they use. But what do I know? I am just a beginner in gas airplanes.

Lots of good information in this thread. I think I in the future will cut the my engine using the choke (at idle) or by cutting the ignition.
A question on the side. MVVS (or evolution in my case), warn about letting the engine running backwards. My engine occasionally runs backwards aften starting. In some cases I do not realise untill increasing throttle to taxi. In some cases the engine may have been running backwards for as long as 20 - 30 seconds, at idle. Does this harm the engine? Or is this warning similar to the choke warning - that it doesn't matter as long as it is at idle?

How do you do that from the transmitter? With a servo? An optical kill? It is an AMA requirement that you are able to kill any Gasoline engine from the transmitter. Manually grounding out the spark is not acceptable.

I would agree that cutting the spark off is a logical and elegant approach. The choke still seems jury-rigged.

Bill

Do your comments also infer that the choking crowd is operating the choke manually? Just curious?

Bill