Ok guys, got an issue that I can’t get figured out. It would be much appreciated if I could get some input on it.

I have a BME 50 that was bought used and came with some baggage.

First issue was that it had a CH ignition with the external grounding strap, which is a great ignition, but the plug boot was pretty worn out. I changed the plug boot to the metal cap style. I tested the ignition and all worked well.

The second issue was that the carburetor that came on the engine was a HLIC brand, which is not the stock carburetor (WT-201b) normally used on the BME 50. Being that this engine has some miles on it, and not really having a good idea of the history of the engine, I figured that the carburetor would need a rebuild. So instead of tracking down a rebuild kit, I decided to mount a DLE 55 carburetor (NIB, WT-664A) that I had lying around. I set the needles to 1.25 low and 1.5 High prior to first run.

First Run: Before I had got the parts in to fix the CH ignition, I ran the motor with the WT-664A carburetor and an RCEXL ignition. The motor ran great, transitioned well, good top end power (7300 rpm with a Xoar 21X8), but I noticed it had a slight miss at WOT. I did adjust the needles during this run. Ended up being about 1.5 turns for the low and 1.75 for the high.

Second Run: CH ignition and the WT-664A carburetor installed. Motor started fine. I let it warm up for about 2 minutes. After warm up, I went to throttle up and the engine started missing pretty bad and would not obtain full throttle without dying. After couple of restarts, I realized that this was not a tuning issue, but an ignition issue. One more attempt to restart and the motor would not fire. At this point, I figured that I did something wrong during the plug cap install and had fried the ignition. I brought the airplane back into the shop, and started to troubleshoot the ignition. Come to find out, the ignition tested fine, but the halls sensor had gone bad. I ordered another halls sensor, installed it and tested the ignition. Worked like a champ.

Third Run: CH ignition with new halls sensor and WT-664A carburetor installed. Started fine, top end was still good, but the transition sucked. If the engine idled for more than a few seconds, and you tried to accelerate the engine quickly, it would die. No stumble, no cough, just die. If you cycle the throttle from wide open to idle with little or no hesitation at idle, it transitions great. Normally I would think this is a lean low needle setting, but I have adjusted the low needle from 1.25 turns to over 3 turns with the only change being that the top end started to suffer around 2.5 turns richer on the low.

Could this be an air leak? I would think it would effect the whole throttle range and not just with a rapid acceleration from idle.

Could it be an ignition problem?

Could it be that the WT-664A carburetor is not suitable for this engine?

Any input would be great.

Thanks

Back off the high needle a little. Too tight a high impacts the low, making the low side real hard to deal with. Peak the high, then peak the low, afterwards backing off the low until the transition is good both at quick throttle changes and fater a period of sitting at low RPM.

Thanks T.O.M., I will give it a try.

Well, still no luck. Peaked both high and low and slowly starting richen the low to get some kind of transition with the same results as stated in post one. I noticed today, that really any position below about half throttle it will die if you quickly advance the throttle. If you slowly advance the throttle or cycle the throttle from full advance to idle without stopping it runs like a champ.

Set up:
BME 50
Stock Banjo style muffler
CH ignition and Rcexl ignition
NGK BPMR6 .023 gap
Stihl HP Ultra 40:1
3/32 fuel line
Fiji Gas 16 oz tank
felt clunk
Xoar 21X8


Things I have tried so far:
Two different carburetors.
Changed the carb adaptor gaskets.
Two different ignitions.
And tons of needle turning

Things I have not tried yet:
Re-plumbing the fuel system
Tearing down the lower case of the engine and sealing it back up. (I don't see any evidence of leaking around the engine)
Purchasing a WT 201b carb for it. I would think the WT 664A would work just as well.


Any more suggestions would be great....

Thanks

Sounds like time for a good carb cleaning then. Could be crap trapped in the high speed circuit which would kill the engine after about half throttle. A rebuild kit costs about $10.00 and takes about half an hour or so to do. Pick up a can of spary carb cleaner and a can of compressed air for cleaning computers and such and clean everything out. Replace gaskets and diaphragms while in the process.

They are quite easy to do. Just track the order the parts come off and replace in reverse order.

I haven't been using carb cleaner lately. I repair a lot of small engines, and I had regular carb spray ruin several check valves in carbs for me. Admittedly this only happened for me on Zama carbs, but it made me "gun shy" of using the old faithful carb spray anyway. Now I soak the carbs in mineral spirits, then use WD-40 to blow out the various passages. Never had a problem doing it that way....

AV8TOR

T.O.M. normally I would agree with you, but I have used 2 different carbs. and one of them was NIB. I would be hard pressed to think both had had trash in them.I have gone through about 5 16oz tanks trying to tune it. The fuel goes through two filters prior to seeing the engine.

Do you know the difference between the WT 664A and the WT 201b? Is the 664A just to small of a carb?

Thanks

Not grounding the ignition will kill the hall sensor, the spark can be seen jumping the gap between the magnet and sensor...20K volts is a little high for the sensor,,,,
The plug wire has a braid around it to be connected to ground..Either the steel cap or the cylinder....

Antique

Are you thinking the hall sensor could be acting up? Would you get those kind of symptoms from a bad hall sensor? When I replaced the cap on the ignition i did connect the braided wire to the metal cap with a metal clamp and also silver solder.

Thanks

Remove muffler and try open exhaust. May be restriction.

Good points.

As for a NIB carb being a problem, it happens all the time depending on where the carb was made. If you have a Taiwan or Japan carb it will normally be ok but a Mexico or China carb often has issues. Unfortunately you have no way of knowing which you have.

The hall sensor wires could have an intermittent connection.
Open the plug gap to about .035 just for kicks....026 is for CM6s...Shouldn't make any difference unless the gap is too small, or over .060...

Guys,

Here is a follow up on this problem.

After fiddling with it more than I wanted to, I decided to start fresh with a whole new ignition system and carburetor.

1. Replaced the hall sensor, and used a brand new Rcexl ignition
2. Made sure everything was sealed up good.
3. Installed the new WT 664A carburetor.

Running it in this configuration yielded no better results so I decided to order a WT 201B carburetor.

Next run.

1. New hall sensor and Rcexl ignition.
2. WT 201B carburetor (Factory Carburetor for this motor).

The engine ran like a champ. I was able to finally put a good tune on it. I wouldn’t think the difference between the WT 664A and WT 201B would have made that much of a difference. I am no carburetor expert, so I can’t claim to know why it worked, but for some reason I could tune the 201B and not the 664A on that engine.

Thanks for all the help.

Hi T.O.M. Need your help or anybody that could give me a solution. I have been adjusting Walbro carbs for years and my Trusty "Pressure Pop-Off" unit #500-505 does not hold pressure. It appears the Flapper valve is worn. See Picture. I can purchase a new unit for over $200 from Walbro and $80 from a distributor. I had hoped to get a Re-Build kit but it appears there isn't any. Does anybody know if I could get a replacement valve or re-build kit? Any help would be appreciated. Col. Chuck Winter

Did they both have the same throttle bore/ venturi size? Just wondering if the one that worked had a smaller bore. I'm having the same bog issue on my Rotomotor 170 and wonder if it needs a smaller carb.

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