I had a problem with my Buell and thought other Buell users could benefit from knowing the symptoms and what the solution was....
The bike: 2003 XB9s 8k miles, Buell customer race ECM and Buell race exhaust - otherwise standard and been running perfectly for years. In England so air temp is 10-20c. Symptoms:
1, Until a few months ago it would start instantly from cold without touching the throttle - then it needed the throttle opening a little before it would fire up - but after that ran OK. If you stopped it seconds after first starting it and then it would restart instantly without needing to touch the throttle.
2, The first symptom remained and then as it warmed up (say 10 mins into a ride) it became reluctant to take normal/moderate/large rapid opening of throttle with hesitancy and flatness like either being choked or ignition timing out. Would accelerate if throttle opened very slowly, but not past 5.5k Then if you stop bike and leave it whilst hot for a while - 10 mins plus it runs much worse - starts on 1 cylinder and then takes a few minutes of riding before other cylinder starts. This leads me to think the heat of the parked engine is "soaking" into the faulty item making it worse - but after 10 mins riding the passing air has cooled it down enough to let it function well enough for both cylinders to run - but same flatness/hesitancy. Occasionally after very gently opening the throttle for a while it will then take larger throttle openings without the hesitancy/choking.
Initial thoughts pointed to intake seals. I checked them and they were perfect and put a new set in just to be sure. Same problems remained. I changed the intake seals without dropping the engine - a little fiddly but do'able.
The Check Engine light did not indicate any trouble codes (it comes on when you start the bike and then goes out - if an error is stored then the light comes back on). To double check I used the manual error code approach of connecting the two right-hand ECM diagnostic cable connection pins to see if the ECM had any stored errors and it had none. Next I connected a Buell diagnostic tool - ECMDroid to the bikes ECM via a special bluetooth dongle. This also showed the bike had no error codes. I had perversely hoped for an error code or two to point me at the problem - but nothing. I wondered if the fuelling was out and too lean or rich but the bike didn't smell rich (petrolly smell) and the ECMDroid software allows you to check the fuelling via Adaptive Fuel Value, or AFV settings and my one was showing 104% so in the green. The throttle position sensor seemed to be working as expected and showing 5.3° so within range (5.2 - 5.6) and the bike ticked over from cold at 950-1050 rpm.
The workshop manual is very comprehensive with test data and flow charts to test out all of the main elements and sensors. All the sensors seem to be fed 5v and they return a voltage from this that indicates their state - so as an example the Throttle Position Sensor sends back 0.5-1.5 volts at idle (closed throttle) and 3.9-4.9 volts at wide open throttle. The ECM monitors these voltages to run the bike -if any of them were faulty then the ECM should detect it and hold it as a trouble/error code. As the ECM had recorded no such faults, it seems as if all of the sensors etc were working fine. I could manually check the voltage of every sensor to double check, but that would take quite a while and if the ECM did not detect a fault then probably they are OK.
Without any error codes to give me a clue - the main help I had in finding the solution were the symptoms. These seemed to point at multiple sensors/things being faulty that got worse after the hot bike had been parked for 10+ mins - and no error codes to give any clues - confusing!
I went to the pub to ponder. It seemed unlikely that the bike had developed two separate faults - much more likely to be just one causing a variety of issues. I have ridden Ducati's for 30 years and also 100 years old Triumph bikes - so plenty of experience of odd behavior to gain experience from!
The 2nd symptom only happened after the bike had been left hot for 10 plus mins so my reasoning was that this faulty item had to be remote from the engine and somewhere covered where heat soaking from the engine would build up but not in free air as it then took 10 mins of riding for it to cool down. The TPS and coil were possibles but I think they would have heated up with the engine and after another pint, the under seat area seemed the ideal place where the heating up/cooling down scenario would match the symptoms as would the coming together of all of the sensor wires at the ECM. The next morning I had a good look at these wires and they all looked fine externally but I noticed that the grey ECM plug was not fully seated - just a tad/mm out from being fully pressed down - could that be it? I pulled out both connectors and used electrical cleaning spray and had a look at the insides - all looked fine so connected it all back up and made sure grey connector was fully seated.
Bike fired up perfectly with no need for any throttle. I have now ridden it five times and all is back to being perfect - problems seemingly solved. No idea how this connector could be loose as it hasn't been apart since new. The bike is a very early XB - made October 2002 so maybe it takes 15 years for vibes and bumps to work the connector a tiny fraction apart.
Thought this worth posting to help out anyone else with misbehaving Buell and maybe worth checking your connectors to see if they are working themselves apart.