Actually this is more about running issues than simply not starting.
At various times, I thought it was fuel and or ECU issues.
I also noticed posts with references to intermittent loss of power. I hope what I found can help someone else. After all, our STs aren't getting any younger....
I may have found the bug in my electrical system.
I could never figure why the bike ran worse after the 6m tune-up. That's when it started the intermittent loss of power. It started on the ride home and I attributed it to a lean mixture. Figured the Shop adjusted it to be environmentally correct- lean.
I messed with the mixture. It'd run better; much rejoicing. Then it would show its ass again.
Couldn't trace it to fuel or electrical.
I checked all the grounds and connections for good seals. I started to think about fuel pump/filter issues and it made some sense. I bought the gear to fix it.
After 1 mixture adjustment, the R/R caught fire- Ah, there's your problem.
After much time, I got a new one. I won't go into details. Lets FF to after I got That fixed.
Meanwhile, I replaced the fuel pump, filter, and hoses. The hoses were disintegrating leaving black crap in the tank. It wasn't too bad, though. They weren't leaking.
Bike started w/good charging, but still would run "cobby".
I replaced the battery and remade all the connections. I put a big-ass ground from the battery to the frame. I added an extra ground from the R/R mounting plate to frame. I used dielectric grease on all connections. It charged great; topping out at 14.2v when 1st starting.
I rode it 10 miles w/o loss of power. I rode it more and more. Even though it was running OK, it was still not as smooth as it used to be.
I fixed the routing on the battery ground, and it started running rough. Now, how does a ground wire short to ground?! Put it back and it ran OK- for a while.
I rode it yesterday morning, getting ready to ride it more; started missing again. It was like I rolled off the throttle. It didn't cough nor sputter; just lost power.
I pulled the rear spark plug to check it- it was black & rich. Oh, BTW, the spark plug boot came off too easy.
I crimped the connection in the boot and put it back on. It was still rich with black smoke on startup. I had tried to adjust the pot on the new/used ECU, bit it wouldn't turn. The more I thought about it, I knew the mixture had to be off because the ECU came from a different bike.
I put just a little WD40 on the screw and massaged it. I got it to move to a leaner position. It ran better and I repeated it; still good, still not as smooth, though. Sometimes, it would smooth out and I had my old ST back.
I thought about it some more and took the spark plug boot off- still too easy. I crimped it some more and got more of a positive fit. The boot uses the big connection with the spark plug adapter on the plug. I like the ones w/o the spark plug adapter needed. They snap on better.
I rode it again and it ran much better. This morning, I pulled the plastic and checked everything. The front cylinder's boot was on tight. The rear was much better. The plugs are a nice tan.
I also noticed that I had wire-tied the plug wires nice and neat; running parallel on the frame. I think that isn't good, as it can leach power from the wire.
I also noticed the plug gap is .023- pretty weak. I emailed Dyna ignition to see if they had HO coils for a Ducati. Hell, my '84 Guzzi plugs gapped at .025 before I put Dyna coils on. A modern ignition oughta gap at .030, at least.
So, anyway, I'm going to see if I can get new wires at Autozone or something. They aren't weird nor integral to the coil or anything. I'll bet the wires are pretty weak. I've never replaced them. I'll route them so they don't contact the frame much.
So anyway, here's the scenario; see if it makes electrical sense:
• Bike ran crappy after 6m service.
• I didn't see that they did anything to cause it; oil, plugs, adjusted valves and such.
• Shop didn't replace fuel filter (red herring)
• Shop replaced plugs and didn't notice plug cap connection weak.
• I ran the bike for several hundred miles with it running rough; losing power for short periods, but not stopping.
• R/R finally smoked.
• Replaced R/R
• Noticed the 40-amp fuse at the battery was dead- fixed with a fuse from NAPA, where the Ducati shop gets their fuses
• Ran for about 5 miles before bike died; wouldn't restart
• Thought it was fuel pump/filter and replaced all; already had the parts since I thought that was the original problem
• Still wouldn't start
• Found it wasn't getting spark.
• Replaced ECU; bike started, but ran cobby
• Redid all + and – connections using dielectric grease
• Ran the best after I made a good fit on the rear spark plug.
Diagnosis:
The poor connection on the spark plug not only caused poor running, it allowed excess voltage to go to the R/R and ECU, eventually frying both.
Phil
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