Post a pic of the muffler to ID it, but the Buell "race" muffler has 2 outlets.
Don't try to 'fix' the ECM. You don't even know if it's bad. No need to open a can of worms by guessing, until you diagnose whats happening or it will cost you time, money, and frustration.
Read this:
http://buellmods.com/content/downloa...olt_manual.pdf
Yes it's boring, but if you want to play mechanic, thats where real mechanics start. Guesses will only cost you time, money, and frustration.
What do you mean by "constantly fouls plugs". Like:
(1) you go for a ride, stop for lunch, and it won't re-start?
Or
(2) After sitting for a month or 2 in the garage it won't start until you clean the plugs?
There is NO physical difference between a Race ECM and a OE one. The fuel program can be modded in either one and the OE ECM you bought is a big mystery, so I'd leave it on the shelf for now.
Normal operation with either a Race ECM or stock ECM will NOT foul plugs, no matter what muffler you have. The only difference between the OE and Race program is when you are at Wide Open Throttle*, ONLY. Any other starting/riding/idling and the bike is in OE map or CL (Closed Loop) and using the O2 sensor to target for stoic/clean running.
What WILL foul plugs is starting it (or repeatedly attempting to start it) and not riding it for a minimum of 10 miles. Buells have a very rich, very long cold start program, many times I get this complaint and it's simply a matter of someone getting bored enough, they keep going out to the garage during winter and thinking that starting the bike every month is a good idea. It is NOT. It WILL foul the plugs and be much harder on the bike and the battery.
Buell rule: If you start it, ride it. They are fine sitting for months at a time on a Battery Tender. Even a year is OK with crappy Ethanol gas in it, but try to make your last fill up before winter, Ethanol free gas.
Whether you swapped the ECM or not, now you NEED to do a TPS re-set. Follow the instructions in the manual I linked for you, EXACTLY.
Now you can begin to diagnose the bike by swapping the plugs (what plugs are in there now? XB's love Iridiums), to get it to run, ride it for 30 miles to let the ECM adjust and then you can check the ECM settings. I found ECMDroid (Free on GooglePlay) to be the easiest to use for diagnosis. It uses a wireless bluetooth connection to the bike (I like the "Buelltooth" one I got from Rev-mo.com),
PLEASE don't get suckered thinking that putting in a 'tune' or messing with the fuel program in any way will magically fix your issue, you don't even know if you have an issue yet. ...Time, money, frustration....
Once you use ECMDroid, check the AFV value, and EGO CORR value under ECM parameters (instructions on Rev-mo.com). They should both be around 90-110. Anything outside those parameters and the ECM is trying to overcompensate for something like a leaky TB gasket, clogged air filter, sticky injectors, lazy O2 sensor, etc.
Get that far and post up what you find.
TL;DR
RTFM
TPS re-set
Clean the plugs
Check AFV and EGO to see whats next.
*simplicity warning