Rebuilding GSM026's BME-115

[flatfuse]

Kris,
Been there-done that. By modifying the carb (both low & high speed circuits) I was able to get very good results. As you describe, It ran ran great except in mid to low throttle during a roll to KE. (this makes rolling circles/harriers difficult at best) I then tried stuffing the reed block and it really did not help. Every time I hear another person suggest that I adjust the needles It just makes me cringe. I have been far far past that and am really looking for a fix to the positional problems as you are now discovering. It's the winter wonderland around here so I am at a stand still. I hope you can find a fix. It will certainly save me some time in the spring. My next thought was to add a venturi baffle (ie a fine mesh screen between the carb and reed block looking for better fuel atomization)

[KrisW]

	Quote: Originally Posted by flatfuse
	Kris, Been there-done that. By modifying the carb (both low & high speed circuits) I was able to get very good results. As you describe, It ran ran great except in mid to low throttle during a roll to KE. (this makes rolling circles/harriers difficult at best) I then tried stuffing the reed block and it really did not help. Every time I hear another person suggest that I adjust the needles It just makes me cringe. I have been far far past that and am really looking for a fix to the positional problems as you are now discovering. It's the winter wonderland around here so I am at a stand still. I hope you can find a fix. It will certainly save me some time in the spring. My next thought was to add a venturi baffle (ie a fine mesh screen between the carb and reed block looking for better fuel atomization)

The mesh screen is a good idea, but may not have the durability needed for this application. Your reed block stuffing is not really as extensive as I have already done on my other 115, so it was probably not much of a help. I barely scratched the surface with my design, so the continuation of the process will yield better results in the end product.

The main concern is velocity, and helping the air make the turn toward each cylinder. To that end, and intricately contoured set of pieces is needed, not just a couple of blocks that fills in the reed area a little bit. You'll be able to see what I mean when I get some pics of the setup in place.

As for "discovering" those positional problems. . . I did that over a year ago. The Diverter/stack style exhausts are about the only place it occurs with the current carburetion setup. Before BME changed to the WB-25, no tuned exhaust I had would run properly, showing just how BAD things were 15 months ago when I got my 115. The basic cause of the problem is still the same today as it was then. . lack of flow velocity, and lack of a good pressure pulse to the carburetor to give accurate signals to the fuel metering circuits. both can be addressed with a properly designed inlet system.

[dbcaster]

Kris,
I have always felt the 115 was setup more towards top end rpm with too large of a carb, intake, and reeds. I looked at it like a tunnel ram on a small block Chevy. Great top end but not too good driving around town. It is nice to see someone actually acknowledging this and not just saying lean the top and richen the bottom. I am sorry but I went through every carb setting possible and there was no middle ground. It is either too rich or too lean. If I leaned mine out enough to get rid of the burble, it would dead stick. I really hope you can find a fix that everyone can use.

[flatfuse]

Whoo Hoo...Go Kris!
You are certainly past where I have been. I am really not capable of doing much more myself and I look foreword to your intake "experiments".

[aviti]

There was a thread on RCU a year or so ago with the same issue on an older 3W 100. One of the guys who was trying to fix it is Dmcquinn on Flying Giants. I believe Dave eventually gave up on the project but it will be interesting to see what you come up with Kris.

[GSM026]

Neat, Kris. Sorry I haven't commented yet, been working 15 hour days this week.

I hope that you can fix the problem once and for all. I had neither the time (or really the knowledge) to deal with it further, and (after trying about every possible needle setting known to man), I was convinced that there was no "right" setting. I'm also pretty well convinced that the midrange problem is worse at high altitudes.

One thing I did not see Kris mention (maybe I just missed it). He found a crankcase air leak where BME had stacked two gaskets. This may have contributed to hard starting and could have contributed to the lean / incipient detonation problem that apparently occurred somewhere in the 60 flights I put on the engine.

Anyway, I am going to be following this as well. And, even though I had baffling before I am improving the design with a better sealing to the cowl and better air control around the head ends and spark plugs. I want to make sure that the 110 stays cool.

Thanks again Kris,
Greg

[rcign]

Want to try something else ? get a 3W right angle velocity stack, or make a copy from a right angle plastic pipe fitting from the hardware store and a brass fititng.......Plug the holes in the steel carb cover...put a fitting in the center of the cover..connect the fitting in the cover to the fitting in the stack......Face the stack FORWARD so all the incoming air goes into the carb....In addition to the 2 or 300 rpm increase, it might just fix the other problems.....It WORKS on a test bench and on the 289cc drone engines we use for racing...The engines were mounted in the back as pushers, the carbs faced forward with air ducted directly into the carbs...The carbs were special castings using Walbro parts with no pump function, and had a small brass tube in the intake that went into the cover over the diaphragm...There are no other holes in the cover....The carbs used crankcase pressure to deliver fuel to the inlet needle...You could do the same to the 115, put a one way valve in the crankcase and pressurize the tank...No problem with too much pressure, any Walbro takes way more than crankcase pressure to force fuel past the inlet needle...Now you have air velocity, fuel in the carb, and the incoming air pulls fuel from the chamber under the diaphragm like it was designed to do in the first place....
Worth a try, nothing else seems to work.....

[KrisW]

	Quote: Originally Posted by rcign
	Want to try something else ? get a 3W right angle velocity stack, or make a copy from a right angle plastic pipe fitting from the hardware store and a brass fititng.......Plug the holes in the steel carb cover...put a fitting in the center of the cover..connect the fitting in the cover to the fitting in the stack......Face the stack FORWARD so all the incoming air goes into the carb....In addition to the 2 or 300 rpm increase, it might just fix the other problems.....It WORKS on a test bench and on the 289cc drone engines we use for racing...The engines were mounted in the back as pushers, the carbs faced forward with air ducted directly into the carbs...The carbs were special castings using Walbro parts with no pump function, and had a small brass tube in the intake that went into the cover over the diaphragm...There are no other holes in the cover....The carbs used crankcase pressure to deliver fuel to the inlet needle...You could do the same to the 115, put a one way valve in the crankcase and pressurize the tank...No problem with too much pressure, any Walbro takes way more than crankcase pressure to force fuel past the inlet needle...Now you have air velocity, fuel in the carb, and the incoming air pulls fuel from the chamber under the diaphragm like it was designed to do in the first place.... Worth a try, nothing else seems to work.....

HAHAHHA. . Around here we call that "Stupid-charging" the engine .. heheheh. . Ram-air inlets DO work for top end power. I'll go that route after I get the idle/midrange problem fixed. who knows, maybe the 115 can turn even HARDER now.

ONa serious note, though, IU'll be attacking this from two directions, and using two ideas, then comparing the two in order to see which is most effective. Test flights will be next week, so I better get cracking, eh?

[Hinckley Bill]

Okay KrisW...

You blew by me about 3 pages ago with your description of the problem and possible solutions so I'm sure hoping your efforts continue to a final solution.

In the meantime........should I just avoid installation of the BME 115 in the H-9 Sukhoi and stick in a tried and true DA-100 to be on the safe side?

Bill

P.S.......let me know when I can send my 115 to you for "modifications".....hehehehehe

[KrisW]

	Quote: Originally Posted by Hinckley Bill
	Okay KrisW... You blew by me about 3 pages ago with your description of the problem and possible solutions so I'm sure hoping your efforts continue to a final solution. In the meantime........should I just avoid installation of the BME 115 in the H-9 Sukhoi and stick in a tried and true DA-100 to be on the safe side? Bill P.S.......let me know when I can send my 115 to you for "modifications".....hehehehehe

Give me a week.

[KrisW]

AH ! ! !

Screw it ! ! !

Gimme 6 hours. . here's your steenkeen fix !!!!!

NO, that is not an SDC-80 carburetor that is usually used ont he 110's.

Now, I'll start working on the induction modifications for the reed block and carburetor currently installed on the 115's. Then I'll do some comparison testing next week. Whichever system proves to provide the smoothest power band, hopefully without losing top end rpm, will be the one to use.

Be sure . .I'll keep everyone apprised of how things go.

[RTK]

Nice work there Kris, do you ever sleep
Looks like the reed block off of a 110????? If so keep an eye out for signs of leaning at WOT.