I purchased a new BME 44 w/CH Syncro Spark ignition second hand (never been run) and installed it on my Midwest CAP. I fired it up for the first time on some 32:1 Lawn Boy Ashless and ran a tank of gas through it on the ground. Filled it up again and flew it around at half throttle or less. After about 10 minutes of flying it started to run very strange at half throttle or just above and landed thinking it could be a fuel low level issue.

Filled up the tank, charged all the batteries and ran the plane on the ground and it ran fine at half throttle or below. As soon as you bring it up past half throttle the RPM varies rapidly at a high rate (steady rate of couple of times a second large RPM flux). Changing the high and low needles had very little effect. I thought that the ignition was the most likely suspect so I called CH and they suggested I send in the motor.

I sent the motor in and got it back less than two weeks later with a note that they changed a part in the ignition and ran the motor and adjusted the needles. I was very excited that the problem was solved. Yesterday I installed the motor and to my horror I had the same problem upon running up the engine. Fuel tank and Batteries were the only thing left I could think of that may be causing the problem. I put together a brand new Dubro tank and connected it to the engine and the problem persists. I tried a different 1400 JR pack directly attached to the ignition and the problem persists.

How can this be? If it were a carb problem CH would have noted it when they bench ran it, assuming they bench ran it. I believe they did as the spark plug and clamp were missing when the engine was returned to me. I also tried a different plug and still am having the problem.

The easiest thing I can think of the determine whether or not it is an ignition problem is to stick someone elses ignition in it. Unfortunately none of our club members have one lying around and I don't want to ask them to pull one out of their plane. Any suggestions?

Thanks for your opinions!

The difference may be that it was run on a bench and your running it in a cowl. A friend of mine had a similar problem and he found that turbulent air was interfering with the diaphragm on the carb. He attached a small piece of plexiglass over the diaphragm hole. Not covering it completely but just a small gap between the hole and the plexiglass. problem solved. I have heard of guys soldering a brass tube over the hole alos and that seems to work also.

Well, it seems to behave the same with the cowl on as it does with the cowl off. And as mentioned it ran fine on the first tank of gas and for 10 minutes in the air. There was a specific point when something changed in flight that caused the problem. I would think if it were a turbulence problem it would have been present from the beginning. P.S. I just took a look at your BME 44 on your web site. It's the same motor and prop I'm running, but I have to run the stock BME muffler.

Never...I had that same problem on a Brison 2.4...was running fine then started running craappy...I to charged the ign. battery ,swithced batterys instaled new plug and finally found it to be the sensor pickup gap was to wide...dont know how it changed but brisons are imbeded in plastic and maybe the heat or something. all i did was push on it and hold it there ...runs fine now...maybe your pick up sensor has changed, is loose...I have brand new BME44 on a Sig Extra 300xs ...waiting for the wx to break here in Mi...then its going in a Great Plains Pitts Special that I havent even started building yet..cant believe BME recomends 20 gals of fuel to break in the motor before switching to synthetic oil. Keep us posted on your progress....
Dont ya just love these problems? never something simple eh

Ron

Yeah, I'll be happy if I can even get 20 gallons through it. It probably doesn't even have a half gallon through it at this point. As far as the pickup sensor, that was the first thing CH asked me about when I called them, and in fact we had already checked it before calling. I guess I'll call BME and see if they will take a look at it. Maybe it's just not to be.

Good luck with the Pitts! I've got their little Ultimate. It does some pretty wacky stuff but I'm sure the big gasser would be even more fun. I'll post my results if I ever get the problem resolved.

I am by no means an expert but would suggest calling Keith at BME. He is EXTREMELY helpful. Are you running fuel filters? It is possible the screen in the carb could have ingested some debris and is plugged up. Also, Keith reccomended I silver solder a piece of brass tubing over the atmospheric vent on the diaphragm cover and running a piece of fuel tubing inside of the fuse. It seems that if the carb is not completely isolated it will richen due to a false atmospheric pressure signal from prop blast or airspeed (maybe both). I did this and the difference in smoothness at low/mid throttle was unreal. He also recommended going with 40 or even 50:1 on the mixture to keep the engine from carboning up which will also cause it to run erratic. As I mentioned, these are just some ideas. If it is an ignition problem I cannot help.
Stick with the engine. Once you get it sorted out, it is a fine running and powerful motor. Good luck, cbk

I had the exact same symptoms last year. Engine started and ran great for exactly three minutes and then it ran crappy and acted like it was alternately going way lean then way rich. I tried everything, put a kit in the carb, swapped tanks, ignition batteries, ignition switch, you name it. Sent the engine in twice, both times it came back with a message that it ran great on the bench. Didn't run great on my bench! Finally talked the ignition mfgr. into sending me a new module which I installed. Problem solved immediately.

After you have exhausted all possibilities, try another ignition. CH are good people and they might send you another module.

I couldn`t figure it out for about 2 days, I talk with Bill over at C&H and he walked me thru all the checks you do on the ignition module and the pickup.
Everything check out okay and my battery was reading 5.4 volts.
I went out to fly.....Aeroworks 29% Edge 540, and the same thing happened again 3 min. in flight and the engine cuts off.

Oh well, when I got back to my shop I pulled the cowl again and the spark plug wire. I rotated the prop sharft back and forth passed the pickup sensor and the spark was inconsistent.

I pulled the Ignition module off the plane and put a spare one on that I had, and all is well now.
The engine is back to its reliable self again.

C&H should be getting my old one in the mail for repair any day now.

You said CH adjusted the carb needles, DID YOU readjust them??? CH is @5400ft and you are @sea level. You can not use the same settings.

I sure did. I went from very lean to very rich on both high and low end. Although as the richer you run it the frequency of the rpm fluxes reduce it is because the engine is running so rich it only is producing half the RPM it should at full throttle. I'm almost certain it's an ignition. I'm about to call CH and explain the situation again and purchase another ignition with the hopes that they will offer to take the old one back if I am correct. I hate to sink anoter $150 into it though in case I am wrong.

I finally called CH ignitions and asked them if they would send me another ignition as I strongly suspected I had a bad one. They were very nice and promptly shipped another ignition. That BME now sings! I still can't figure out how it could possibly have ran properly on the bench. It was one sick motor with the old ignition. Oh well, it'll get another flight test this weekend!

Thanks for all the suggestions...

In my last post I claimed that the problem was solved when I put in the new ignition. Turns out it was only solved for the short yard test runup. When I got to the field the problem magically reappeared. At that point I thought it was time to put a for sale sign on it. Well I called Terry at C.H. Iginitions and apologized for being an idiot, and that he was right in thinking that it wasn't an ignition problem. He gave me some more suggestions, some of which I had tried and some of which I *thought* I had tried.

That evening I reluctantly pulled the cowl off and strapped it down in the yard again. The first and easiest thing I could think of to try first was to grab a different battery and plug directly into the ignition bypassing the switch. I started the plane and it ran perfectly. Now I'm starting to feel stupid, yet a large grin began to grow. So now I've narrowed it down to either a battery or the ignition switch. So I plugged the original battery directly into the ignition and it again ran perfectly. You got it, a bad switch! It was a brand new JR switch that lasted exact 1/2 of a flight and then decided to give me a month of headaches. I certainly must have been imagining that we bypassed the switch in our initial trouble-shooting because I flew it 4 times today and it ran like a dream.

The odd part was it ran very well at idle, all the way up to about 1/2 throttle. Once I got above half throttle it would start a very steady and nasty surging. I guess when the engine vibration got to a certain frequency it caused the switch to have an open condition until the engine dropped back down below a certain RPM in which case it would close and run up again. At any rate. I *strongly* suggest you seriously check the switch if you have a similiar problem. Check it twice just to make sure you really checked it the first time!

I want to thank Terry for bearing with me and I promised him that I would post my ignorance for the rest of the world to see, and hopefully benefit from.

Signed,
Embarassed but happy Never2Windy

I had the same problem on my BME 102 twin. I asked around the IMAC list and this is what the problem was:

BME's like the low needle to be LEAN. Turn in your low needle as much as possible (until it won't transition OK, or just plane quits or won't start). Set the high needle to rich for breaking in.

As far as I know, the poblem does not show up on the ground, or on the bench, only in the air. Mine had the RPMs going up and down, up and down when at about 1/2 throttle. This is where the high needle kicks in.

After leaning out my low needle, my BME 102 runs like a dream.

Regards,
Craig.