stalling when rolling on the throttle (carbed 900)?

[junior varsity]

I'm back. Here's what I know it isn't:

It isn't the vacuum petcock.
It isn't the vacuum fuel pump (replaced).
It isn't the fuel lines (replaced).

It isn't the tank vent or drain hose (checked, clear).
It isn't the fuel filter (new).
It isn't the fuel (new).

Today's Symptoms:

Turn bike on. Idles and revs nicely. Things get warmer, bike idles and revs fine. Bike gets warm after many minutes idling, begins to backfire loudly when revving before ultimately dying if I keep trying to rev.

Info on Bike:
DynaCoils, Ignitech, Nichols Flywheel, Open Airbox, Sil Headers/Pipes, Mikuni CV Carbs that have been jetted.

[ducpainter]

Have you verified that the slides are lifting?

Have you looked at the plugs?

[junior varsity]

I haven't verified that they are once its warm and starts misbehaving. When its cold, I can peer down the intake and see everything seeming to work as its supposed to.

Sparkplugs (NGK) are new since last long ride (before this began).


What are the symptoms to worn jets? Anything like this? I'm trying to guess here.

[ducpainter]

I haven't verified that they are once its warm and starts misbehaving. When its cold, I can peer down the intake and see everything seeming to work as its supposed to.

Sparkplugs (NGK) are new since last long ride (before this began).


What are the symptoms to worn jets? Anything like this? I'm trying to guess here.

The mains don't wear, and needle jets will make it run

rich at low throttle openings/cruise...

but it wouldn't die.

When it dies will it restart?

[junior varsity]

immediately. and resume idling normally to mock me, but if you whack open the throttle, dead. If you wait a bit, you can crank it up, rev up and down normally, and once its warm it'll die when you try to rev.

So if you go inside to have a glass of water, come back out in a minute after your wife kicks you out of the house for being dirty and smelling like gas/exhaust/solvents, etc, you can start it up and its like nothing is wrong... for a minute. Then its warm and it dies when you roll on the throttle.

[ducpainter]

I know you said you have new fuel.

Humor me and use some type of ethanol fuel treatment.

[junior varsity]

the more research i do, the more I'm thinking its not the gas anymore since I've put in fresh Shell 93.

How likely is it that I've got an intake gasket leak at the heads or at the carbs on a 1999? Carbs were pulled off about a year ago for a quick turn throttle to be installed but I've ridden a thousand or more miles since then. Do the gaskets at the head/manifold junction age and leak?

[junior varsity]

i will humor you though. seafoam ok with you or must i go to autozone and poke about until i find some specific ethanol treatment

[ducpainter]

the more research i do, the more I'm thinking its not the gas anymore since I've put in fresh Shell 93.

How likely is it that I've got an intake gasket leak at the heads or at the carbs on a 1999? Carbs were pulled off about a year ago for a quick turn throttle to be installed but I've ridden a thousand or more miles since then. Do the gaskets at the head/manifold junction age and leak?

I don't think so.

An air leak would have to be very severe to make it quit.

i will humor you though. seafoam ok with you or must i go to autozone and poke about until i find some specific ethanol treatment

http://mystarbrite.com/startron/

They have a store locator.

[alibaba]

I am NOT familiar yet with Ducatis.  However, a general trouble shooting test with my old Brit Iron twins was to get it idling and pull one spark plug wire and keep it running by playing with the throttle to see if it performed the same on either cylinder.

Now, I do not know if you can keep a Ducati running on one cylinder.  But if you can, this may help you isolate the problem or give you further insight.

Beware, with some electronic ignitions, an ungrounded plug can damage the system.  You can usually get around this by 'fettling' a small coil spring between the spark plug and the cap and attaching a wire to the spring.  I use a tricked out clippydoo (male only) for this attachment.  Then, after starting, grounding the wire by touching it to the engine thereby killing the spark to that cylinder.  Perhaps our resident electronics gurus can comment on if this is safe on Ducatis.  Howie?

[brad black]

sounds like you're ruling out things because they're new or fresh or you don't think it's an issue without actually doing anything.  have you drained the float bowls or looked at the plugs yet?  if you drain the bowls crimp the fuel hose between pump and carbs to keep fuel in the line.  and catch the fuel as it comes out of the bowls so you can look at it.

you can also hook up a clear hose to the float bowl drain and hold it up the side to see the fuel level as you run it on the stand.  this will tell you if there's a fuel supply issue at all.

try refitting the original ignition units if you have them.

[Howie]

I am NOT familiar yet with Ducatis.  However, a general trouble shooting test with my old Brit Iron twins was to get it idling and pull one spark plug wire and keep it running by playing with the throttle to see if it performed the same on either cylinder.

Now, I do not know if you can keep a Ducati running on one cylinder.  But if you can, this may help you isolate the problem or give you further insight.

Beware, with some electronic ignitions, an ungrounded plug can damage the system.  You can usually get around this by 'fettling' a small coil spring between the spark plug and the cap and attaching a wire to the spring.  I use a tricked out clippydoo (male only) for this attachment.  Then, after starting, grounding the wire by touching it to the engine thereby killing the spark to that cylinder.  Perhaps our resident electronics gurus can comment on if this is safe on Ducatis.  Howie?

A Duc actually runs pretty well on one cylinder.  The plug wire should be grounded before starting.  From the symptoms ato is having the problem is affecting both cylinders.  I think ato will find the problem  if he does what brad black says.

[junior varsity]

sounds like you're ruling out things because they're new or fresh or you don't think it's an issue without actually doing anything.  have you drained the float bowls or looked at the plugs yet?  if you drain the bowls crimp the fuel hose between pump and carbs to keep fuel in the line.  and catch the fuel as it comes out of the bowls so you can look at it.

you can also hook up a clear hose to the float bowl drain and hold it up the side to see the fuel level as you run it on the stand.  this will tell you if there's a fuel supply issue at all.

try refitting the original ignition units if you have them.

I pulled the carbs yesterday (drained floats first, gas ran out fine). There was no visible gunk in the carbs in the bowls, on the floats, or whatnot, but I blew compressed air through the passages to unstick the things I could not see. They are reassembled and ready to go back to the bike.

I tested the vacuum petcock using a mightyvac and pumping into a gas can and it performed fine. Pumped when the mightvac supplied vacuum, quit when I released the vacuum.

So later today I plan on putting the carbs back on, and seeing where we are at now with Ignitech. If it still malfunctions, I'll throw the stock ignition boxes on and give that a whirl.

[koko64]

Gday AM

I wonder if the fuel flow is keeping up with the engine. Since the fuel pump is new I wonder if its worth bypassing the petcock. Can the seals/diaphrams in a faulty petcock be affected by heat/age and restrict flow when they are 'on the way out'. Actually, Ethanol and other additives in fuel may affect the diaphrams and seals over time.

I had to modify the vacuum petcock on my NC30/VFR400. It ran fine until I used sustained high revs. As the petcock's internals aged it began to starve the motor at higher revs. Removing/rearranging the seals and diaphrams turned the petcock into a gravity type. Is there a similar mod for the Ducati one?

Since everything around it is new, I'd bypass the petcock, go gravity feed to the new fuel pump, and see what happens.

[junior varsity]

Y'know, I had the same idea while a buddy was over in the garage with me yesterday, and he said "vacuum petcock. seems overly complicated. What's wrong with a simple on-off valve".

So I logged on here and began looking about. It seems others are using a Motion Pro 5/16" petcock as a suitable replacement. Fair enough. Its only $15, I'll order it up.