Desertrat

My Feedback: (2)

I have a BME 100 that I just installed, and am breaking in. I got the idle down nicely to a not so shaky 1300 rpm, and I'm topping out at 5900 on an NX 26x10. It has about a gallon of fuel through it so far. It transitions nicely on the ground, except when held at mid range RPM (2500-3500), it "hunts" for an RPM, leaning and richening. In the air, mid range throttle settings are very rough, lots of popping and burbling - I have to admit, the "problem" seems to be getting better as I run more fuel through it. Kind of a PITA because this is the perfect level flight throttle. At full throttle and idle, it runs great, on the ground and in the air, its not overheating, nor does it seem too rich.
Is this the classic "put a tube on the static port" problem?

Ed Vollmer

My Feedback: (14)

You should be getting a lot more RPM than that on a 26-10 NX. I think you are too rich on the high end. Some of the midrange problem will go away when you lean it out.

You can also put a deflector plate on the front of the carb. A 1/32 thick aluminum plate just larger than the diaphram cover spaced slightly out from the cover should do it. This makes a dead air space that keeps incoming airflow from affecting the diaphram.

Desertrat

My Feedback: (2)

I thought so too, I called Keith Baker and asked, he says the old 100 aint gonna get much better than that till I get a few more gallons through it, and in defense, it is still pretty tight. I think with a Mejzlik 26x10, it would pull closer to 6200-6300, havent tried it yet. The NX seems to be a tough prop to turn, very stiff, and wide. The thrust is fine, its on a 23 - 25lb airplane, will hover at 1/4 throttle, and it rockets out of it. If I lean it much more it gets pretty hot, with no increase in RPM. I've spent a lot of time with the tach and screwdriver on this motor thinking the same as you - been doing it like the instructions say, maybe I missed something?
As for the front air dam, the cowl is pretty tight fit around the carb, certainly blocking any air that could be causing roughness over the venturi, doubt thats the problem as its smooth as silk at full throttle and idle, but what the heck I'll try it. I guess my real question is am I waiting for the diaphragm to break in or am I looking at a pressure problem, or something totally different....

Ed Vollmer

My Feedback: (14)

Mejzlik 26-10 is what I am ran on mine. I believe it ran about 6800 or 6900 after break-in. It got pretty noisy in the air at full throttle.

Sounds like you just need some more run time on the engine. Are you ducting air through the fins. That makes a big difference for keeping an engine cool. It may allow you to lean it out some more and still stay cool.

There is a pic of my deflector plate in my gallery (click "gallery" below). Go to the DA100/CAP album and look at pic DA5 and DA2.

The air ducting I did in the cowl is also there.

CrashMeister

My Feedback: (4)

The BME likes a very lean low end. Make the low needle as lean as possible while still getting good transition when you goose it. This will help remove the 'hunting' or rpm ups and downs at mid-throttle. Keep the high end rich while running it in.

Craig.

Desertrat

My Feedback: (2)

Ed: Is that deflector plate you have just over the static hole on the front of the carb, or does it bend around over the venturi as well? Nope, no baffles yet (btw, yours look very nice!), the engine is staying quite cool, so I havent bothered with it - in all honesty, I didnt think about being able to lean it out a little more with better cooling, so thats on my to do list now. 6800-6900 sounds like the numbers on a 102, I have the older 100, according to Keith Baker, the best I can expect is about 6500 on the Mejzlik after break in - I just dont like the Mejzlik props, I seem to get better power (and less noise) from the NX or Menz even at lower rpm - personal preference I spose. I too am starting to believe all the engine needs is more fuel. Seems to smooth out more and more with time, and the RPM just gets better, up to 6k now with another 12oz through it.

Craig: thats exactly how I have it set up per Keith Baker, if I let the low end richen up, it tries to shake the tail feathers off at idle.

Thanks for the help guys, and any other input is appreciated!

Ed Vollmer

My Feedback: (14)

The deflector on the DA is just a flat plate. I do have one as you describe that bends over the carb inlet on a 3W120. I did that because the carb inlet is in the airstream also.

I must apologize, my current BME is a 102 and the numbers came from that recollection. I did have a 100 and there is quite a power difference between the two. So, 6500 is probably a good number for the BME 5.8/100.

I set up all my "new" engines by peaking the top end and backing off a couple hundred. Then set the low end to just get good transition when bumping the throttle from idle. Go back and peak the top end and back off a couple hundred. Then re-check the low end.

After eight or ten gallons, I start to peak the top end and just back off 50 to 100 RPM. As it becomes well broken in I will just peak it and watch for heat problems on very hot days.

I direct incoming airflow all my twins (whether they need it or not) because it is easy to do, adds very little weight, and gives me confidence that I will not have any heat problems. I have used 1/32" plywood and 3/16" foam board to make them. Be sure to leave some air passing over the spark plugs and caps because these get hot also.

Diablo-RCU

My Feedback: (1)

Last week I put the tach on a BME 5.8 twin running a Menz-S 26x10 prop - 6,400 rpm. That engine already broken in.