Ducati Monster Forum

This bike is starting to drive me crazy. When I got it, it was not running perfectly, but running. Valve adjust, adjusted and sync'd the carbs. Was running great, that night. Ran great for an hour, but got up in the morning and fought it dying at lights the whole way to work. It straightened up when I was almost there. Same on the way home. My assumption was a carb issue, and I had no idea what had been done internally to the carbs to account for the exhaust and air box mods, so I pulled the carbs. Not too dirty, but had some bad orings and the enrichers looked all chewed up.  Car and blow out the carbs. Replace rubber, enrichers, and needle jets in the carbs. Reassembled and dial in the carbs. The bike is running great. I ran it pretty hard. Only a little flat spot at 3/4 throttle. Felt like silk through the rest of the rpm band. This morning, dying, sputtering, backfiring through the lower rpm range. I pull on a bit of choke and it would clean back up, but did that the whole way to work. Actually seemed like through the entire rpm range by the time I got to work. It seemed fine for the first few blocks. Any thoughts or experience like this. My thoughts are still leaning towards a fuel problem since it cleaned up by turning back on some choke. Just not sure what would cause such an intermittent problem. My next though is leaning towards the fuel pump/ vacuum petcock and see if one of them is restricting flow sometimes causing the fuel bowl to get low, creating a lean condition. Maybe 

What year is your bike?  The fuel pump system gave me fits on my '97.  You can bypass the petcock pretty easily and run fuel straight to the pump. 

You can also temporarily bypass the fuel pump as a diagnostic procedure.  The fuel level in the tank has to be higher than the carb bowls though. 

What did the fuel look like in the bowls when you did the carbs?  Fuel tank supply and vent lines not restricted or kinked?  Fuel line from pump to carbs?  Is there vacuum in the tank when you open the filler cap?  How is the fuel filter?  Vacuum lines to the pump and fuel shut off?

The fuel was clean. Nothing in the screen going into the carb. I couldn't find any kinked hoses. Still had the issue with the tank open. It is a 99 model. I am going to start digging deeper in the fuel system. Thanks guys. I think I shud start by seeing if the fuel level is low when it is having the issue by hooking up a clear hose to the fuel overflow. It should let me confirm whether or not it is a fuel delivery issue or a vacuum leak causing the intermittent lean condition.

Change the fuel filter if it isn't new. They are only like $5 at an auto parts store.

I can change it out, but what car filter does it change over to? I got the clear fuel lines on the overflow tubes and opened the bowls.
 (http://i195.photobucket.com/albums/z22/bigjohn_73/IMAG0932.jpg)
Here is the height of the fluid. I have not seen anything that shows what the fuel levels should be from the outside of the carbs with the factory pro kit installed. I did get both sides even with each other. The fuel height is consistent from right to left. I did set the both heights to 14mm from the highest point on the float to the face of the carb. They seemed to move up and down about a 1/4 inch while I was reving the bike. Not sure what that variation should be.

http://www.ducatimonsterforum.org/index.php?topic=32659.msg568665#msg568665 (http://www.ducatimonsterforum.org/index.php?topic=32659.msg568665#msg568665)

It's the Luber-Finer 3407. They may not have that exact model, but they can get you a direct swap.

OK
replaced the fuel filter, bypassed the vac petcock, changed spark plugs......

no change. It maybe sounds worse. backfires and pops if I rev it. I guess next step is checking the fuel pump. Anyone have a favorite method. It would be pretty straight forward if you didn't have to disassemble half of the electrical system to get the air box off.
Not that it is That big of a deal, but as a design engineer I really don't see the point of it being that way other than an engineer that took absolutely no consideration of serviceability

Bypass the pump with a full tank of gas and see how she runs.

I tested the pump and then pulled it apart. I disconnected the fuel line from the pump and started it up to run just on what was in the float bowls. It did seem to pump gas. I seemed like not very much volume, but of course a carbed bike doesn't need that much. I went ahead and tore the bike down again. I dissembled the pump.
(http://i195.photobucket.com/albums/z22/bigjohn_73/IMAG0933.jpg)
No smoking gun. The diaphragms seem a bit stretched out but there isn't a tear or anything like that. I may tear into the carbs again while I have the airbox stripped off of it, but I am really not sure what I am going to look for other than making sure nothing is blocked and that I have not got a vacuum leak somewhere. I figure I do need to go ahead and order a pump rebuild kit. I was hoping to source it locally, but the ducati place only wants to sell an entire pump for over 100 bucks.   

Those diaphragms look just like the ones that were in my dead pump.  Do not buy a Winderosa kit.  The diaphragms tear with the result being a vertical cylinder full of fuel.  Sudco has genuine Mikuni kits  http://www.sudco.com/CatalogJPG/507.jpg (http://www.sudco.com/CatalogJPG/507.jpg)  The pump they show has one more outlet, but the kit is the same.  As you can see, the volume is huge.  That pump is also used on some Polaris products and I hear they sell kits

 The pump kit is ordered. Now the waiting......

Electrical problems can sometimes appear like carburation problems.
If the bike runs great sometimes and for no apparent reason, starts acting up, I'd look at the ignition system.

Just saying.

George

I am up to hear any experience this direction. It has a good hot spark. New plugs. It now consistently backfires when I try to add any throttle from idle (at least it did before I tore down the fuel pump). And will continue to backfire while I hold steady thottle.

You checked the air filter to make sure there wasn't a rats nest in there?
How about the slide diaphragms? A rip in one will make it break up.
Are both cylinders acting up or just one?
The bike was running, but not perfectly when you bought it, then started acting up after the valve adjustment carb adjustment and sync.
Who did the work?

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.

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.

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.

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.

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? 

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.

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?

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?

Sorry

This is a M750

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.