Fuel issues at higher RPM (i think)

[erkishhorde]

At least I think that's what it is. My bike's been sitting in the garage for about a month waiting for me to dismantle, send off for parts, wait and then put it back together. It had about 3/4 tank of gas. I start her up in the driveway and everything seems fine. I take her around the block, ok. I try to gun it at a stop sign and she goes but not as fast I remember. Then when I hit the free way I start noticing surging. It goes on for a little bit before I realize it was actually surging. Thought it was crazy wind at first but then realized I wasn't feeling any head buffeting or anything. I realize something is wrong and let off the throttle and the bike sputters a bit. Pull the clutch and give the throttle a few twists and I get increasingly less response from the bike. I manage to coast off an onramp after the bike dies. Pop open the tank, yup there's fuel. Try to start and it works just fine.  Go to the gas station and top off w/ some premium. Hop back on the freeway and I get the same thing. Bike dies on me before I reach the next exit so I pull over and after a couple tries the bike starts up again.

So I head home on surface streets and the bike runs well enough. I can cruise around at 40 no problem in 1st-4th gear. Too long at 40mph in 2nd gear and the bike starts to complain. Too long at 40mph in 1st gear and I start to complain and then the bike does too. If I suddenly give it more throttle in 3rd or 4th the bike will kinda choke and I'll get a very delayed response or no response at all (no increase or decrease in speed). Unfortunately I can't pinpoint an RPM that gives me problems because my tac is out.  I'm thinking maybe the fuel filter is clogged or some kinda fuel pump problem? (Do I even have a fuel pump.... Carby bikes still have a pump, right? I haven't had time to look in my Haynes manual yet...)

I hope it's a quick fix... Life isn't fun right now and I need my bike. 

[Oldfisti]

I don't have much experience w/carb bikes but the fuel filter is a good place to look. Do the carbs have floats and are they stuck in the up position? A plug check wouldn't hurt. See if the color is odd or inconsistent between cylinders.

[Howie]

Yes, you do have a fuel pump.  If you still have the OEM item it is the hexagon shaped thing with a vacuum hose and two fuel hoses.  Changing the gas filter won't hurt.  I would start by checking hose routing first.  Then I would remove the air filter and make sure carb slides are not sticking/stuck.  After that I would drain a little bit of fuel out of the carb bowls into a clear container and look for water as well as other contaminants.  Water will sink to the bottom.  If you are running fuel with alcohol in the fuel the water will be grey and slimy.On the left side of the bike you will find two plastic hoses by the rear brake lever.  Follow them up to the carb bowls and you will see brass screws, 8 mm. heads if I remember correctly.  Loosen them and the fuel will drain.  When you tighten them snug is good.

[erkishhorde]

So, clean the carbs, change the fuel filter and see if that cuts it. If not, change the pump? Kind of a "duh" question but just to make sure.... The gas tank has to be empty to change the fuel filter? I assume it's in the gas tank. Am I wrong? I'm at work and can't look at my Haynes manual  but I wanna try to get an idea of how much work needs to be done.

[Howie]

At this point, if the slides are free and the gas comes out of the bowl clean, I wouldn't clean the carbs yet.  Even if the fuel in the carbs is yucky (not a technical term ) I wouldn't clean them yet because I am lazy.  Your filter is located under the tank.  The tank doesn't need to be empty, you can just pinch off the line into the filter.  If you found water and dirt in the fuel, this would be a good time to empty it though.  If the tank is very full raise it with two hand and support it with a board from the middle so you don't strain the hinge.

I don't think the problem is the pump, though it could be.  Before replacing or rebuilding it, do a pressure check.  I never saw an official Ducati spec, but I think around 3 PSI would be a good figure.  From your description of symptoms if the pump is bad I would expect a very low reading.

[Ducnial]

Before you dump a bunch of money into a new fuel pump measure the voltage going to pump and check fuel pressure first.  Either do it yourself or take it to your local shop.  Check the spec for your particular bike (S4Rt =3bar or 43.5 psi).   If the pressure is medicore at an idle and drops like a rock when you twist the throttle it has a restriction somewhere e.g.  dirty filter or pinched hose. If it is constantly low regardless of throttle position fuel pump is probably toast. 

[erkishhorde]

How do you measure the pressure out of the pump?

[Capo]

The machine in question, has carburretors not fuel injection.

[Howie]

How do you measure the pressure out of the pump?

In the case of your carbie pump, T fitting in the fuel line from the pump to the carbs and a good ol' fashioned vacuum/pressure pump.  Run engine, read pressure.

[Speeddog]

Also, check to make sure your fuel lines aren't kinked when you set the tank back down.

Had a bike in recently that had a high-speed fuel starvation issue, the line from the fuel filter to the vacuum petcock was kinked so bad I'm surprised it would run at all.

[BastrdHK]

I am betting its moisture in the float bowls.....we drained and cleaned the carbs on an '01 m750 b/c it was running inconsistently/dying.

[greenmonster]

Old/bad quality fuel lines can slowly collapse, letting by less & less fuel.
Check that it ha´s`t gone soft in the middle.
Fuel filter is another possibility.
Fuel pump diaphragms about to give in a third.

[erkishhorde]

Replaced the fuel filter and all seems to fine.