Fuel problem on carbed monster

[Big John]

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 

[thebronze]

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. 

[Howie]

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?

[Big John]

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.

[Dellikose]

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

[Big John]

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.
 
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.

[Dellikose]

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.

[Big John]

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

[koko64]

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

[Big John]

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.

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.   

[Howie]

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  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

[Big John]

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

[transplant]

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

[Big John]

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.

[transplant]

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?