Fuel problem on carbed monster

[Big John]

Fuel pump rebuilt, but no change. Backfiring the same as before.

It does seem to be getting worse instead of better. I have done all of the work. I have been building bikes for years and was a mechanic for two decades while I got my engineering degree and now design valve train components. It is driving me nuts that this stupid bike is kicking my butt. Talked it over with ducati mechanic. Says I have done and checked everything he would have based on the symptoms.

Starts and runs fine for a minute, then begins to loose power and backfire.
Not really something that can be diagnosed online, but I appriciate all of the ducati insight into things that might be ducati specific. It has to be something stupid and small I have missed.

It is great to have a place to vent how much I am regretting buying this sorry piece of garbage that only runs right with the choke on.

[tbyte]

Has she been left out in the weather?  If so you may well have water in gas.  Bad gas can cause all the problems you named.  Drain carb floats into clear container and check gas.

[transplant]

Gas and air check out, so it must be spark.
Is it one cylinder or both acting up?
If it's one cylinder, switch out the coil, box, and wires and see if the problem follows it to the other cylinder. If it does, then it's just a matter of switching individual components to isolate the bad actor. Don't rely on specs. I had a bad coil last year that ohmed in spec, yet would fire intermittently at idle. If you've done that and still the same cylinder is bad, it may be one of the HES sensors or it's wire is bad.
If it's both cylinders, I'd look at the HES, all the ignition related wires and connectors. Pull the fuse box out and make sure all the connectors are tight. I had a friend a few years ago that suffered through months of intermittent stalling because of a loose fuse box connector.
I'll assume you load tested the battery, checked the charging system, and all your grounds are tight and corrosion free.
Keep us posted.

[koko64]

Was thinking the same.
From what I can tell from way over  here.

Just did a job on a T150 Trident. Had simultaneous carb and ignition issues that gave the owner grief for years. John may have fixed the fuel starvation issue. He proved it was a fuel starvation issue when he did the choke/enrichener test. As long as the floats and needles are now set correctly after the carb rebuild and not too rich once she gets hot.

An ignition component could be complaining at higher operating temps. Not uncommon. A fine wire fracture opening when hot, an ignition pick up faltering when the oil gets hot, etc.

My view is that there was more than one problem since John is an experienced mechanic. Wouldn't be the first time as many of us know!

Good luck John. Watching with interest.

[Howie]

Fuel wise all I have left is the hose from the pump to the carb collapsing when hot.  Electrical?  All has been pretty much said but check coils for resistance when hot.  Tap them to simulate vibration on the bike while testing.  Will the bike start backfiring if you let it idle or do you need to ride it? 

[Big John]

Thank you for all the help. Not sure if this is going to help anyone, but the bike is running fine now.

I was rechecking the timing one last time before I tore it down entirely and just started checking each componenet One by one untill I found the issue. I had seen the night before that there was a flame coming from the tailpipe when it was backfiring that seemed to be there whether I had the screws a half turn out all the way to 6 turns out. I decided to check out the timing advance one more time to make sure it wasn't contributing to the issue.

So I have hooked up the light; I am trying to get it to idle to check the un-advanced timing and it keeps dying like it has been. I hit on the choke and find a spot where it is just barely running. I finally start reving it up to check full advance, and all of a sudden it dawns on me...it is not backfiring. i take the choke off all of the way and it is idling smoothly (for a ducati anyways). I have been riding it and all of my drivability issues are just gone. I flogged it for about 20 miles so far today and seems fine.


Been trying to put some kind of answer to it and I haven't really come up with one. I had gotten gas, but I still had the issue for a good ten miles after i had filled it up. I was trying to ride it and get the fuel level down just a bit when I saw the backfiring was shooting flames.

Now it just has a bit too fat mixture at idle (not a surprise since it is 6 turns out) and seems a bit lean from about 4-6000 rpm. I figure i can go up a half on the needle and see what that gets me.

[Big John]

Just a little jetting info.
I am having a little trouble getting it dialed in. I think part of the problem is that, since it was modified before I got it, I have no real baseline to compare it to. It does feel like it bogs when I roll on the throttle from a 3000 rpm cruise in anything but 1st gear. Also it doesnt seem to have as much pep up top as I was expecting, but again, I don't know how much I should have with this bike.

I know the bike has a 135 main and a 45 pilot. It has an aftermarket needle (I suspect the needle and spring are Factory Pro because of the jet sizes installed). At 2.5 turns the bikee feels pretty strong down low, requires choke when cold but just for a couple minutes. I tried moving the needle from #2 to #2 with a washer to raise the needle a half step, but didn't seem to have much effect and possibly made the pull from 3000 worse. It felt more choppy like it was bogging down than like it was soggy (too rich), but I think I need to assume I am getting too much gas right there instead of not enough if it got worse by raising the needle.

All of that, just to ask, about when should I feel power drop off on this bike? Around 8000? 7500? Or should it have more?

[koko64]

If it's a 900  then power dropping off at 7500 is normal with stock length manifolds. 750s hold their top end a little better. Doug Lofgrens MPS site covers this.
If its a 900 then 135 main jets are lean, (unless Doug has fitted one of his custom emulsion tubes). If the bike has an open air box then thats real lean.

What modifications on the bike?

[Big John]

Sorry

This is a M750

[Big John]

I haven't had time to get on here, but the bike is running much better. Tested at wide open throttle and 135 looks to be perfect. I have tried the needle at 1.5 to 2.5 and the #2 looks to be right. Right now I can turn the screws to 1.5 turns and the soggy spot right at 3000 rpm goes away, but gets a little lean right at idle. 2.5 cleans up idle but has rough patch at 3000 rpm. Was emailing with the guys at Factory Pro, working through the carb issues on this bike and he has suggested me going from a 45 to a 42.5 pilot jet. I have to say, I have had bought and had several bikes with Factory Pro jet kits and they have all worked very well. I was already to a point I recommend them. This was the first time I have used their service/tech help and now I am totally sold on them. Not only were they very helpful, but they answered emails fast, were friendly, knew their stuff, and when I asked if I could get a part from them, he sent me a paypal link within minutes and it was on the way to my house. Done. I just got it last night so I haven't gotten a chance to install it yet. Maybe this weekend since it is raining here.
I have been enjoying the bike. Realized I have put 1700 miles on it in the last few weeks. I am thinking I will throw it on the dyno and get HP and fuel ratio numbers once it feels like it is running clean.