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Discussion Starter #1 (Edited)
1996 Ducati 900SS

- New DynoJet Stage 2 kit:

150 main jets, DJ needles (4th clip from top, per instructions), 37.5 pilot jets, brand new OEM emulsion tubes, K&N air filter in open airbox, 14MM float bowl, idle screws backed out 2 turns, Cycleworks coils, DP AL-9000 CDIs.

The bike is extremely difficult to start up. It will absolutely not start with the air filter on. I have to hold the starter button for about 3 seconds and when it begins to fire I have to hold the throttle just a wee bit to keep it at 1,200 RPM, otherwise it will shut off. It sounds wet and soggy, and after a hard ride, when I start it up, it blows out a little black smoke for 1 second; just one big cloud of maybe 20% opacity? It's mostly air.

Then, when opening the trottle completely, the RPM will take about 2 seconds to reach 1,800 RPM, at which point it immediately launches into proper revving.

I took apart the carbs. I cleaned every single passage I saw, including the air passages on the side of the butterfly's, air pilots, float bowl valve chamber, even the choke plunger and passages. I checked the pilot jets and they seemed perfectly circle without any debris. I checked the idle screws' o-rings and they seemed fine. Re-installed, nothing improved at all.

My friend then realized that he had messed with the sync screw at one point, but "only a little". I cannot recall if the bike was running properly before or not, sorry. Since it was already touched, however, I decided I can experiment with the synchronizing screw until I have it synchronized with an actual tool, but I did not notice any visible effect on the idle. Given, to sync them (from memory) means they are finely tuned, and I was very aggressive with the screw. But it was worth trying I thought.

Is what I am describing possibly a simple synchronization issue?

I am not sure if this is related, but there is some relatively large blow-by ending up in the airbox. The oil from the crankcase does not smell like gas. And the rectifier is a little weak (13.5 volts max) and I was wondering maybe that's affecting the quality of spark in the low end? Not sure how it all works.

Cheers.
 

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That voltage is a little low - it should be around 14 - 14.4 volts. You could try (cheapest option) removing all the earth straps - battery to frame, frame to engine, and cleaning them (sand them shiny) - including sanding the paint off the frame at the attachment points. Reassemble with a light (very light) dab of Vaseline to prevent further corrosion. And yes, that low voltage will affect things - especially at start time, when the starter drags on the battery. That's one reason to do the earth straps (leads). Check your voltage at the R/R output to a good earth, and again across the battery - they should be the same (I just fixed a bike - non Ducati - that was dropping almost a volt from the R/R to the battery due to a dud main fuse holder).

Errm - when you say you open the throttle completely - what do you mean by that? Do you just whack the twist grip around as fast as you can? Not a good option for those carbs - they don't have accelerator pumps, so the engine will go really lean and bog when you whack the throttle open.

Check all plug connections too - particularly the ones from the alternator to the R/R - the plugs have a habit of corroding, then overheating (they'll look 'blackened' if they've been a problem). Clean shiny (800 grit wet and dry works well), and replug - use another small dab of Vaseline on the connectors if you're keen. Remember - it's an insulator, so too much and you won't have any electrics. ;)

Oh - and try removing the plug caps from the spark plugs, and pull on it - it should be firm, and NOT come off the lead. If it does (it's a screw on type), cut about 1/2" off the end of the lead, and screw the cap back on tight. If those caps are loose, they can cause poor idle, and poor low engine speed performance - almost like a carb problem. Don't ask me how I know. :eek:
 

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If you're talking about your idle air screws being out 2 turns, that may not be enough. You need to adjust them for highest/smoothest idle after well warmed up. Start at about 3-1/2 turns out and go from there. 37.5 may be a little small on the pilot jets. When you start " adjusting" things like the carb synch, write down your starting position so you can return to where you started. What is ending up in your filter box, fuel or oil ? These carbs are sensitive to float height, sounds as if level may be high. There are tons of posts on carb tuning available here, read up on the subject.
 

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Discussion Starter #4
That voltage is a little low - it should be around 14 - 14.4 volts. You could try (cheapest option) removing all the earth straps - battery to frame, frame to engine, and cleaning them (sand them shiny) - including sanding the paint off the frame at the attachment points. Reassemble with a light (very light) dab of Vaseline to prevent further corrosion. And yes, that low voltage will affect things - especially at start time, when the starter drags on the battery. That's one reason to do the earth straps (leads). Check your voltage at the R/R output to a good earth, and again across the battery - they should be the same (I just fixed a bike - non Ducati - that was dropping almost a volt from the R/R to the battery due to a dud main fuse holder).

Errm - when you say you open the throttle completely - what do you mean by that? Do you just whack the twist grip around as fast as you can? Not a good option for those carbs - they don't have accelerator pumps, so the engine will go really lean and bog when you whack the throttle open.

Check all plug connections too - particularly the ones from the alternator to the R/R - the plugs have a habit of corroding, then overheating (they'll look 'blackened' if they've been a problem). Clean shiny (800 grit wet and dry works well), and replug - use another small dab of Vaseline on the connectors if you're keen. Remember - it's an insulator, so too much and you won't have any electrics.


Oh - and try removing the plug caps from the spark plugs, and pull on it - it should be firm, and NOT come off the lead. If it does (it's a screw on type), cut about 1/2" off the end of the lead, and screw the cap back on tight. If those caps are loose, they can cause poor idle, and poor low engine speed performance - almost like a carb problem. Don't ask me how I know.
I can get to testing sometime tomorrow. I will report back with some values.

I open the twist grip slowly to half-throttle. I can't speak for other people, but this bike has always been able to have the throttle whacked open and power wheelie through first gear; I have never had a problem whatsoever with opening the throttle too quickly causing it to bog down in any gear or in any RPM. I've been riding this one for nearly 10k miles now and I ride it very aggressively. It wasn't until I started messing with the carburetor when all these issues begin, and leaving my ground wire loose (which makes me wonder if it affected the RR).

I have a Rick's Motorsports Universal RR. The interesting thing is, when I hook it up to my bike, it burns out the fuel and ignition fuse. The prior owner put a ground-style circle terminal (the ones where a screw can go through it) on the black wire. Nonetheless I hook that black one up to the same black wire the original RR hooked up to (so, it's paired with the white wire). I wonder if I am supposed to bypass connecting the black wire as normal, and actually hook the RRs black wire to the body as a ground, joining the other ground wire that comes from the bike.

I double checked the leads and they seem very solid.
 

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Discussion Starter #5
If you're talking about your idle air screws being out 2 turns, that may not be enough. You need to adjust them for highest/smoothest idle after well warmed up. Start at about 3-1/2 turns out and go from there. 37.5 may be a little small on the pilot jets. When you start " adjusting" things like the carb synch, write down your starting position so you can return to where you started. What is ending up in your filter box, fuel or oil ? These carbs are sensitive to float height, sounds as if level may be high. There are tons of posts on carb tuning available here, read up on the subject.
The idle screws don't seem to be affecting anything when adjusted in or out.

It's oil. For every 20 miles about 1 tablespoon of oil is in there. I am usually on the freeway and am topping out a lot.

That pilot jet is stock size. What makes you say it might be too small? I figured if it was in fact too small, Dynojet would have identified that after numerous times of testing there jet kit for this bike, but I could be wrong. I don't know =/

The float height went from 12MM to the current 14MM. I did not notice a difference. This manual says all Ducatis should be at 14MM, but Salvisbergs' tuning guide implies simply to do whatever works. But let's say I go as low as 10MM; is that something anyone has ever done? For some reason it concerns mean having to go so low. I guess I'll have to try it out.
 

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I think with the float level it's kind of a complicated adjustment, and individual judgement comes into play. I set mine " by the book " and yet one carb would overflow when warm, at stoplights and such. I just lowered that bowl a hair. I mention the pilot jet size because stock is a little lean, then if you have pipes or air filter mods it gets leaner. The bike won't run well near idle and may not idle until really warm. Common pilot size with pipes or mods is 40 or 42.5. If your air screws are not responding at all, that circuit is plugged and it won't idle . My air screws are out 4-1/2 turns with a 40 pilot jet. The air screws are still adjusting mixture at least 5-1/2 turns out. 37.5 pilot jets combined with 2 turns out on the air screws is really lean, mine wouldn't even start like that, much less run well. I'd start by backing the air screws out 4 turns and go from there. No idea why Dynojet recommended so small on the pilot jets. Their kits have always turned my bikes into horrible gas guzzlers so I don't use them. You can resynch your carbs by eyeball or using Allen wrenches as Gages probably good enough . The gaskets on the jet holder and fuel seat inside the float bowl can leak causing uncontrolled fuel getting by them. When they're done right they're good carbs, it just takes a bit of dinking around to get you there.
 

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Black smoke is always gasoline. Oil burns white.

Are you saying that both cylinders are the same? Have you examined the plug and cylinder after sitting before starting?

I understand you are having a starting difficulty but does it never idle after that?

I'm not sure where to go without that info but a wild guess would be a leaking float valve or floats set radically too high since you are getting gas into at least one cylinder before starting.

Doesn't sound like an ignition problem. You are igniting raw gas from the get go.
 

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this is the best way to check the float level. as much as people like marc bang on about it, i don't think i've seen one that needed to be adjusted. make sure the bike is level (vertical).

Brad The Bike Boy: Setting float level on Mikuni BDST38 carbs from Ducati Supersport and Monster

assuming you had the carbs apart to do the needle jets, etc, did you put o-rings back under the white plastic slide carrier? if not, it'll run very rich.

usually they won't take throttle from a cold start unless they are quite rich. a 900 would usually only start on the choke when cold.

balance can certainly affect idle on these if it is way off. check it, don't guess.

euro bikes have 40 or 42.5 pilots, usa 37.5. i don't see that as a big issue, certainly not what you've got.

does it have compression? done a leakdown test? closing clearances?
 

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The bike is extremely difficult to start up. It will absolutely not start with the air filter on. I have to hold the starter button for about 3 seconds and when it begins to fire I have to hold the throttle just a wee bit to keep it at 1,200 RPM, otherwise it will shut off. It sounds wet and soggy, and after a hard ride, when I start it up, it blows out a little black smoke for 1 second; just one big cloud of maybe 20% opacity? It's mostly air.

Then, when opening the trottle completely, the RPM will take about 2 seconds to reach 1,800 RPM, at which point it immediately launches into proper revving.
Sounds rich to me, just as Brad and Jahjah mentioned. The question will be why.

Float height effects rich lean but you lowered the level which would lean it out.

The sync in the ballpark should have a good idle.

I have set up hundreds of these carbs with 37.5 pilot jets on a gas analyzer and dyno and the size is fine on 90% of them even modded motors. There should be no good reason for the 37.5 to be rich.
If you have swapped carbs there are early 900 carbs that did come with 40's (like the monsters) that needed the 40 to be correct but your 96 should be fine on a 37.5

Any chance you had the pick up connectors apart at some point? The bike will run poorly if you transpose a couple of the ignition pickups, usually accompanied by a lot of back firing.

High RPM's with Ducatis will often push oil into the airbox, how much depends on ring seal but if it is a small amount after riding at high rpms for a long while it is not uncommon.
Keep in mind reving that engine at or above 8000rpm is going to push oil and go slower.
 

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If the float level is correct and functional, I'd replace the gaskets located under the jet holder and seat holder inside the float bowl. If they leak unmetered fuel can enter the intake causing a rich condition.
 

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Discussion Starter #11
Hey y'all,

Thank you so much for the responses. I just wanted to give an update that I'm overlooking everything again and will respond to each question or suggestion posed insofar.

I can say this so far:

The spark plugs we're fouled as hell. I find it difficult to believe that this was all from low-speed/idle operation. Perhaps I am running rich at top end as well? While I am simply looking to get this thing to idle, I wonder if the Dynojet 150 Main Jet is affecting the low-end circuitry enough where it's making it rich to a problematic degree.

The o-rings that sit beneath the emulsion tubes seem to be fine, but I will replace them anyways. I'm finding it very difficult to order that o-ring only; is there a specific term that refers to the kind of a ring that can be used in petroleum products?

The idle mixture screws are actually affecting idle, in opposition to what I had said earlier. I guess I hadn't paid enough attention to them when I was experimenting with their measurements.

I purchased Motion Pro 5 millimeter intake manifold adapters which is the missing component to my homemade manometer. I should be able to have the carbs synchronized by the end of this week, and if this problem isn't solved by that, we can at least rule that out.
 

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I can get to testing sometime tomorrow. I will report back with some values.

I open the twist grip slowly to half-throttle. I can't speak for other people, but this bike has always been able to have the throttle whacked open and power wheelie through first gear; I have never had a problem whatsoever with opening the throttle too quickly causing it to bog down in any gear or in any RPM. I've been riding this one for nearly 10k miles now and I ride it very aggressively. It wasn't until I started messing with the carburetor when all these issues begin, and leaving my ground wire loose (which makes me wonder if it affected the RR).

I have a Rick's Motorsports Universal RR. The interesting thing is, when I hook it up to my bike, it burns out the fuel and ignition fuse. The prior owner put a ground-style circle terminal (the ones where a screw can go through it) on the black wire. Nonetheless I hook that black one up to the same black wire the original RR hooked up to (so, it's paired with the white wire). I wonder if I am supposed to bypass connecting the black wire as normal, and actually hook the RRs black wire to the body as a ground, joining the other ground wire that comes from the bike.

I double checked the leads and they seem very solid.
OK - Sounds like you've got several problems. Your R/R is dead. I don't know what's going on with that Ricks Motorsports unit - but I wouldn't trust it either. Brad The Bike Boy: Charging system diagnosis procedure is a very useful guide as to testing your charging system out.

Looking at your other responses, I agree with the majority, in that I think you're running rich. As to why... Worst case scenario, is to bite the bullet, and procure a set of FCR's and improve your grin factor. And save a heap of frustration. Yes, the standard carbs can be made to work pretty well. But they'll never be as good as a setup set of FCR's. Just whether you can justify the $'s.
 

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In addition to the comments preceding, and not in contradiction of:

1) New copper plugs gapped correctly
2) New fuel filter, and look carefully at the "sock" for breakdown - if threads are missing they have gone somewhere into your carbs
3) Clean all grounds thoroughly
4) Take a long ride with Seafoam in the tank.

Longshot idea -
How do you tell if your exhaust is plugged? Pipe obviously crushed? I dunno how to check inside the cans, but at least take them off and shine a light in there to see if something made a nest in there. (Don't laugh, I found an old tarantula nest in the muffler on a barn find bike one time and squirrels hide stuff everywhere).

After the 60mile plus ride, pull those new plugs and post pics.

From what you have been saying, I strongly suspect a marginal/intermittent electrical output coupled with a very clogged fuel filter - you might be chasing two problems. I bet your bike idles just fine at 2,000rpm's because the electrical is up. Clogged fuel filter should affect the bike at WOT coming up from 4,000rpm's however, do you still have that performance that it used to have before the problems? Or don't you know because since the problems started you have not ridden it long/far enough to tell?
 

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I have to put scouring pads in my pipes to prevent them being filled with acorns. I've found nests in the air boxes . With no air filter in place, rev the bike several times and watch the vacuum slides rise. Are they opening smoothly and together ? This stuff has been discussed in minute detail countless times in this forum. You should really read the old posts.
 

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How was the bike running prior to the jet kit install? If this behavior started after the kit installation there is about a 99.97 percent chance that something was not done correctly at installation. Follow the instructions and recheck your work.
 

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Did you pull the diaphragm covers ? You might have pinched a diaphragm. Did you replace those little o Rings inside the covers ? You have to. Are the vacuum lines not collapsing, are the inline filters on them clean ? Lots of things it could be, it's old. Stuff decomposes. Things plug up.
 

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Discussion Starter #18
I think with the float level it's kind of a complicated adjustment, and individual judgement comes into play. I set mine " by the book " and yet one carb would overflow when warm, at stoplights and such. I just lowered that bowl a hair. I mention the pilot jet size because stock is a little lean, then if you have pipes or air filter mods it gets leaner. The bike won't run well near idle and may not idle until really warm. Common pilot size with pipes or mods is 40 or 42.5. If your air screws are not responding at all, that circuit is plugged and it won't idle . My air screws are out 4-1/2 turns with a 40 pilot jet. The air screws are still adjusting mixture at least 5-1/2 turns out. 37.5 pilot jets combined with 2 turns out on the air screws is really lean, mine wouldn't even start like that, much less run well. I'd start by backing the air screws out 4 turns and go from there. No idea why Dynojet recommended so small on the pilot jets. Their kits have always turned my bikes into horrible gas guzzlers so I don't use them. You can resynch your carbs by eyeball or using Allen wrenches as Gages probably good enough . The gaskets on the jet holder and fuel seat inside the float bowl can leak causing uncontrolled fuel getting by them. When they're done right they're good carbs, it just takes a bit of dinking around to get you there.
I somehow misread my pilots. They are in fact 40. Idle screws are creating an effect although not to the tune of perfection, or anywhere near it.

I even lowered my float to 11MM. I mean, that's pretty damn lean, but no effect at all.
 

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Discussion Starter #19
Black smoke is always gasoline. Oil burns white.

Are you saying that both cylinders are the same? Have you examined the plug and cylinder after sitting before starting?

I understand you are having a starting difficulty but does it never idle after that?

I'm not sure where to go without that info but a wild guess would be a leaking float valve or floats set radically too high since you are getting gas into at least one cylinder before starting.

Doesn't sound like an ignition problem. You are igniting raw gas from the get go.
After about 200 miles, both plugs are fouled like no other. I am surprised they operate at all. Might be because those Cycleworks coils are so damn strong!

Correct, it does not idle even after I get it to start up. The details of how that happens is in my original post.

That's an interesting guess. I am quite certain both exhausts bellow black smoke upon startup. Will double check tomorrow.

The float valve seems to be fine upon having inspected it. The teeny weeny spring on top of it seemed fine too.
 

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Discussion Starter #20
this is the best way to check the float level. as much as people like marc bang on about it, i don't think i've seen one that needed to be adjusted. make sure the bike is level (vertical).

Brad The Bike Boy: Setting float level on Mikuni BDST38 carbs from Ducati Supersport and Monster

assuming you had the carbs apart to do the needle jets, etc, did you put o-rings back under the white plastic slide carrier? if not, it'll run very rich.

usually they won't take throttle from a cold start unless they are quite rich. a 900 would usually only start on the choke when cold.

balance can certainly affect idle on these if it is way off. check it, don't guess.

euro bikes have 40 or 42.5 pilots, usa 37.5. i don't see that as a big issue, certainly not what you've got.

does it have compression? done a leakdown test? closing clearances?
I changed the float to an extreme 11MM which was supposedly the stock setting for carb'd Monsters. It still has not affected idle.

I replaced the o-rings underneath the slide carrier. The old ones weren't cracked but for good measure I did it anyway.

Btw I misspoke: the pilot is 40.

Compression, leakdown, clearances: I did a compression about 1k miles ago and it was 150/149.

Should I still do a leakdown? Clearances I have not checked. I don't have the tools yet (they're en route from my parent's house).
 
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