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
Quote from: tcspeedfreak on April 04, 2009, 05:41:49 PM
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.
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.
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 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
Quote from: tcspeedfreak on April 04, 2009, 06:00:41 PM
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.
thanks for the reinforcement on what i was already thinking i will know more tomorrow when i can get new plugs
Quote from: tcspeedfreak on April 04, 2009, 06:18:27 PM
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.
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...
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.
Quote from: Duck-Stew on April 04, 2009, 07:09:03 PM
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 [evil]
QuoteYou 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.
Quote from: Langanobob on April 04, 2009, 09:39:17 PM
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
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 ???
Quote from: tcspeedfreak on April 05, 2009, 09:57:57 AM
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.
Quote from: Bun-bun on April 05, 2009, 10:09:46 AM
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.
no the manifolds are not cross linked, im just throwing shit up against the wall and hoping something sticks, cant do anymore untill i can get some carb kits anyway, maybe give a call into the local service shop and see what they say
Both should open simultaneously even at no load conditions when revved. Both of mine did on my 01' 750. I say pull the carbs and see whats going on in there. Maybe just something bound up with crap (carbon, old fuel stabil) or maybe something improperly assembled. you can actually get to that part of the carbs without removing them from the bike but they are easier to work on when sitting on the bench.
thinking thats next weekends project, gotta get carb kits because last time i cleaned them the gaskets were pretty much shot so this time they are gonna be junk
Quote from: tcspeedfreak on April 05, 2009, 09:57:57 AM
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 ???
If the slide isn't lifting...even under a no load condition....
you have a problem.
I think all the usual suspects have already been mentioned.
Time to start digging.
When you find the problem...
the bike will be 25% more powerful. [thumbsup]
No load, they will not lift much, but both slides need to lift equally. Another possible problem not mentioned can be the slide mechanically sticking from gum or (unlikely) wear. Since the slide is moved by a difference in pressure on the diaphragm a little friction can be a problem.
Quote from: howie on April 05, 2009, 07:34:27 PM
No load, they will not lift much, but both slides need to lift equally. Another possible problem not mentioned can be the slide mechanically sticking from gum or (unlikely) wear. Since the slide is moved by a difference in pressure on the diaphragm a little friction can be a problem.
i can lift the slide with my finger and it feels the same as the other carbs slide so i dont think that friction is the problem
You can check the diaphragm by removing the filter and sucking on the hose.
If the slide lifts the diaphragm is OK.
That doesn't eliminate the little o-ring though.
Not knowing how much you opened the throttle when you checked the slides this may be way off, but have you synched the carbs?
Quote from: ducpainter on April 06, 2009, 09:52:04 AM
You can check the diaphragm by removing the filter and sucking on the hose.
If the slide lifts the diaphragm is OK.
That doesn't eliminate the little o-ring though.
Not knowing how much you opened the throttle when you checked the slides this may be way off, but have you synched the carbs?
they were synched last spring i never screwed with them since, and like i said earlier this may have been going on since i bought the bike and didnt even realize it
i maybe had the throttle half open the vertical carbs slide was almost all the way open and the horizontal carb didnt even move
im not able to even look at the bike again untill this weekend so im just a little [bang] due to the fact that i cant fix it right now
well got the horizontal cylinder running right now turns out i was a pinched diaphragm, and a pluged vent hose, somehow full of leaves and shit, how that got in there i dont know damn mice.
but now the trouble is that the vertical cylinder is backfiring and occasionally blowing fuel out the carb.
but she is pulling more than she was before i cleared that line
thinking that i just need to buck up and go through the carbs and get it over with
Quote from: tcspeedfreak on April 10, 2009, 05:49:09 AM
well got the horizontal cylinder running right now turns out i was a pinched diaphragm, and a pluged vent hose, somehow full of leaves and shit, how that got in there i dont know damn mice.
but now the trouble is that the vertical cylinder is backfiring and occasionally blowing fuel out the carb.
but she is pulling more than she was before i cleared that line
thinking that i just need to buck up and go through the carbs and get it over with
How many miles on this?
Try new plugs and a throttle synch first. If the bike was adjusted to compensate for the poorly functioning carburetor that could be your problem.
Quote from: ducpainter on April 10, 2009, 05:52:20 AM
How many miles on this?
12k, had valves done last spring
Quote from: howie on April 10, 2009, 06:08:24 AM
Try new plugs and a throttle synch first. If the bike was adjusted to compensate for the poorly functioning carburetor that could be your problem.
that makes sense but think im going to go through the carbs anyway its been a while, just replaced plugs last weekend. plus have to find someone with a vacuummate before i can sync the carbs