help carburetorated monster guys

[tcspeedfreak]

i have a 2000 m750, I'm pretty sure she isn't hitting on the horizontal cylinder (found this out by pulling the plug wire and no change in idle), i suspect a fouled plug... but at the same time the little vacuum operated power valve looking thing in the carb throat isn't opening upon twisting the throttle but the vertical cylinders does.

so my question is am i looking at an ignition problem or fuel?

my first cheap try at fixing the problem is going to be plugs in the morning but any other input would be great

thanks Tyler

[needtorque]

i have a 2000 m750, I'm pretty sure she isn't hitting on the horizontal cylinder (found this out by pulling the plug wire and no change in idle), i suspect a fouled plug... but at the same time the little vacuum operated power valve looking thing in the carb throat isn't opening upon twisting the throttle but the vertical cylinders does.

so my question is am i looking at an ignition problem or fuel?

my first cheap try at fixing the problem is going to be plugs in the morning but any other input would be great

thanks Tyler

I think you have already found the problem lol.  The slide should open on both carbs simultaneously.  There is a rubber diaphragm in there if I remember correctly from my rebuild and it may be torn.

[ducpainter]

The slide not lifting is an issue, but the plug is probably fouled too. They do that if the slide doesn't lift.

Another cause of the slide not lifting can be if the vent line to the diaphragm housing is kinked.

[tcspeedfreak]

but would a fouled plug cause not enough vacuum to open the slide i seem to remember something like that anyway from something else

[tcspeedfreak]

i should also add that it doesnt want to get out of the hole but once i get her moving she seems ok but still not all there

[ducpainter]

but would a fouled plug cause not enough vacuum to open the slide i seem to remember something like that anyway from something else

I'm not sure...It may very well be the case.

Start with the easy stuff, which would be the plug IMO.

[tcspeedfreak]

thanks for the reinforcement on what i was already thinking i will know more tomorrow when i can get new plugs

[ducpainter]

thanks for the reinforcement on what i was already thinking i will know more tomorrow when i can get new plugs

I'm curious if the slide won't lift if the plug's fouled.

You would think the cylinder would make some vacuum whether it was firing or not just from air entering and leaving the cylinder...maybe not enough though.

Keep us posted.

[Duck-Stew]

The rubber diaphram (sp?) could be torn, but there's also an O-ring between the plastic cap and carburator body that could be cracked, or mis-aligned.  That passage (that the O-ring seals) is a vaccuum passage that's responsible for opening the rubber dia...thingy.

Put the plugs in, but I doubt that's the case...

[Howie]

There are also filters in the breather lines to the diaphragms that can clog.  Rare, but it happens.  If you check out the parts catalog on Ducati.com you will see them.   

[needtorque]

The rubber diaphram (sp?) could be torn, but there's also an O-ring between the plastic cap and carburator body that could be cracked, or mis-aligned.  That passage (that the O-ring seals) is a vaccuum passage that's responsible for opening the rubber dia...thingy.

Put the plugs in, but I doubt that's the case...

diaphragm/vacuum   

[Langanobob]

You would think the cylinder would make some vacuum whether it was firing or not just from air entering and leaving the cylinder...maybe not enough though.

This is something that I never thought about,  but it does seem like it would have enough vacuum regardless of whether the plug was firing or not.  If I get motivated enough tomorrow out of curiosity I'll hook up a vacuum gauge and then ground the plug to see what happens to the vacuum, if anything.

[tcspeedfreak]

This is something that I never thought about,  but it does seem like it would have enough vacuum regardless of whether the plug was firing or not.  If I get motivated enough tomorrow out of curiosity I'll hook up a vacuum gauge and then ground the plug to see what happens to the vacuum, if anything.

now i remember where i learned this,  when syncronizing the throttle plates on multi-cylinder fourstroke engines,  a cylinder not firing will produce less vacuum than one firing.

but still not exactly sure why mine is doing what its doing yet still to earily to buy plugs on a sunday

[tcspeedfreak]

well got new plugs, picked up the horizontal cylinder again but the slide still wont open on that carb

now it seems to be running like it was last year anyway...

but just some food for thought, i know that on automotive carbs like lets say a rochester quadrajet, the vacuum operated secondarys will only open if there is enough load on the engine, they wont open in neutral, so since my bike is on the center stand reving it in neutral should the slides for both carbs still open or since there isnt much for load on the engine will only one?

the bike seems to be running now like it has since i bought it two years ago, but maybe it just has never ran like it should be for me

[Bun-bun]

but just some food for thought, i know that on automotive carbs like lets say a rochester quadrajet, the vacuum operated secondarys will only open if there is enough load on the engine, they wont open in neutral, so since my bike is on the center stand reving it in neutral should the slides for both carbs still open or since there isnt much for load on the engine will only one?

If the manifold is crosslinked, then you may have a valid point, but if I remember, each carb is responsible for only one cylinder, so both should operate exactly the same under any condition.