I am having some troubles withmy engine. I figure that I would post the issues in hopes to find the most likely cause before I start troubleshooting.



Engine BME 110

Mej. 28x10

Belray 44:1

I have about 10 gallons through the engine now and to this point it has performed flawlessly. Today while on my second flight it began running a bit erratic. My best description is it "sounded" like it had a terrible misfire around mid range. Once I opened the throttle up it seemed OK. I have not touched the needles so that seems like an unlikely cause. Anyhow, I landed it assuming that I had a fouled plug. About 30 minutes later I decided to start it up to see how it acted on the ground. Now that it couldn't unload, it was "backfiring" and missing through the whole throttle range. I pulled both plugs and they looked great. They had a nice tan color. I decided to put in new plugs anyway. Now I can't get it to run.



The symptoms now are. Choke on full throttle I flip it till it pops. Usually 3 flips. Then, choke off, set throttle to idle, and flip. After 4 flips it fires and runs for 2-3 seconds and shuts off. I can repeat these procedures with the same results over and over.



I have done no troubleshooting at this point other than changing plugs. Any ideas?

All you need is air, fuel, and spark to make an engine run. My first guess would be that the ignition is bad, or your battery has taken a dump. Check all connections first and see how the battery handles a load. If that is all fine then look for some obstruction (crap) in your fuel system or carb.
Now that I have re-read your post, I would look at the carb first. It sounds like it will run on the prime then quits. When checking the carb to make sure needles, screen, etc. are clean, also check the pulse hole to make sure it is clear.

good post RTK

Yep, sounds like a carb filter screen. I'd check that first in any case.

RTK. Thanks. I'm sure that cleaning the carb screen is a simple process but since I have never disassembled a carb is there a "how to" available?

It is about as easy as falling off of a bar stool Well, that is if you put all the parts back the way they came off.
Start with the pump side. Remove the cover and note which order you removed the gasket and pump diaphragm. Do one side at a time and set everything in order of removal, it helps. Look at the screen under the pump, it can be cleaned, might have to be removed for cleaning. In actuality it isn't needed, but it keeps junk from going down stream any further.
This is probably all you have to do, but if you remove the other side to see if any junk is there, be sure to have the nipple on the diaphragm engaged in the fork of the needle arm when you replace it or your engine will run rich and probably leak fuel. Be careful not to bend the fork when removing the diaphragm. If you do need to take that side off go ahead and remove your L & H needle and blow some air thru them too.

RTK. I pulled off the carb to check the screen. Immediately found the problem. I think. One of the reeds is broken. Will this cause the behavior I described? I am totally ignorant to the operation of these carbs. I wonder if the reed broke which caused the erratic running and backfiring or if somehing else like the ignition caused the backfiring which broke the reed?

Either way, I ned a new reed. Any idea where I can get one?

Once the reed breaks the engine will not run, you have seen this with the choke run for a few seconds then stop. I'd bet it was cracked and finally gave way. Cracked or warped reeds cause very erratic running.
I would call the new BME and see if they have any. You can make one very easy if you can find the right material. If BME does not have one, call Ralph at rcignitions.com. He will be able to point you in the right direction in finding the correct material. If I had a spare I would send it to ya. Good luck.

Measure the thickness of the reed with some calipers. Go to [link]http://www.mcmaster.com[/link] and peruse their catalog until you find a composite sandwich material that is close to the same thickness. Sorry, but I can't remember what the product is called at the moment. Now you have to cut the reed. You can't do that with scissors or a hobby knife. It has to be stamp cut or fuel will eventually wick into the layers of the composite sandwich and cause it to delaminate/debond. The edges also have to be rounded smooth.

Another way is to see if some reeds from a 3w 106 or DA 100 might interchange. Or run down to a saw shop and see what they have laying around in the scrap parts bin.

Good advice Pat

Thanks Guys. I will start with BME.

I was able to order new reeds through BME. I will also check the screen while I have the carb off. Thanks guys.

Will these notches be a sign of an early crack in my engine's reeds?

Looks like one face of the reeds will be more exposed to develop problems like the one carsh90 is reporting, is that correct?

I am sure those will eventually give way. I can't remember what my cage looked like in my 115, but I would call up BME and order an extra pair or make some yourself.

Another job to do on this engine, never mind.

Any idea what does trigger this effect on the reeds?
Any other engine brand (using reed valves) developing such potential problem ?

Everybody has an occasional problem with reeds, they wear like any other part on an engine. The warp, crack or break, but it is not a real frequent problem.