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Discussion Starter · #61 ·
So what size is the factory needle jet?
If you measure the factory needle at the butt and compare it to oem or the old dynojet needle in the same area what size is it?
There are plenty having great luck with factory jet kits and needle jets but imho when you start making changes without knowing what the change is you can end up lost. Oem needle jets are measured and marked different for 600,750,900 etc so what is the needle jet now marked for size? did you get the correct size?
I don't know what the bike is like with the OEM needle and emulsion tube, it came with the Dynojet kit already on it. The needles in Factory Pro kit have numbers, but I don't know what it means, I think they have their own in-house number for it. I have new replacement OEM needles that came with rebuild kit, but the package says it's for 600, 750, 900, doesn't discriminate which one. Those needle says y271. Do you suggest that I try that OEM needle, maybe, even if only to set the baseline?
I opened the left side cover, reset the pick up to it's original place, and shaved 3.92mm off of the flywheel hump (3 degrees). The carbs are apart again, I'm waiting for new gasket kit for them (just in case).
 

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I have new replacement OEM needles that came with rebuild kit, but the package says it's for 600, 750, 900, doesn't discriminate which one. Those needle says y271. Do you suggest that I try that OEM needle, maybe, even if only to set the baseline?
It seems you have a 3rd party rebuild kit. They claim that the needle you have is the same as the 5C19. That needle is the jetting that came on the bikes in Europe.

So, that is the one to go with. If it is a straight replacement, it should have 5 slots. The USA needles that came with the E900 had just 1 slot to eliminate the ability to mod the A/F.

If it was me I would go 1 slot higher which would lean out the mixture. The stumble will either get better or worse. If it gets worse go 1 slot lower than standard, etc.

If you hold the emulsion tube up to a light and peer through it you should be able to see the wear on the lip (you should see it ovalized). Compare it to the new one to confirm you have a new tube. I have received worn tubes in rebuild kits as the only way to see if they are worn is to view through the tube. They can look new otherwise. A new tube will have a perfectly round hole.

Here is the page that shows the kit and the image below is their specs.

Repair-kit-ducati-900-ss-supersport-year-1991---1997-k-1336dk

Thanks,

M./

5C19.specs.png
 
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We are all aware that each adjustment overlaps the next. You also have to be aware that the emulsion tube / main jet starts working at a very low throttle opening, as soon as there is enough vacuum to raise the slide, and with it , the need le, out of the main jet / emulsion tube assembly. This is why a different design of emulsion tube affects almost the whole throttle opening. Main jet only affects wide open throttle ? No, it affects every fuel circuit to some degree. I have found the low speed mixture screw affect idle mixture far past 3 -1/2 turns out. Mine are at 4-1/2 turns. Only adjust these with a well warmed motor.
 
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Try ethanol free fuel and see if the engine still pops. I have found a huge difference in the way my bikes run with it. Even my John Deere runs better on it.
 

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Discussion Starter · #67 ·
Here is the page that shows the kit and the image below is their specs.

Repair-kit-ducati-900-ss-supersport-year-1991---1997-k-1336dk

Thanks,

M./

View attachment 1009351
Eh, yes! That is the kit that I used when I initially did the carb rebuilt when I first got the bike. Like I said, the bike came with the Dynojet kit installed, so I only used gasket and o-rings and stuff like that. Dynojet uses the OEM emulsion tubes. Factory Pro kit comes with the needle and emulsion tube. I never thought of testing the OEM replacement needle just simply because. I'll try that out.
 

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If you’re talking about a needle with the same profile as the stock one you are going in reverse.
 

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Do you own a micrometer?
If yes measure the butts of both needles and compare them. a skinny needle will have a similar effect to a worn needle jet when the butt is the restriction. This will simply allow you to see if the BUTT is richer or leaner and which the bike prefers. Your needle as well as needle jet are aftermarket which means they likely are not going to fuel the same way, I do not know how a factory needle jet flows compared to a mikuni so I can not tell you if it flows more or less than the oem size for your carburetor but I would be surprised if it is not different.

At this point you are likely shotgunning the problem, too many things are being tried. Start with one theory and prove or disproving it but set it back to a known good configuration before moving on to another thing to try. If the bike was improving by making it leaner continue until it no longer helps, if nothing helps return to your starting jetting and then try something other than jetting like ignition.

Are you sure you filed the correct side of the flywheel lump?
 

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Discussion Starter · #70 ·
Are you sure you filed the correct side of the flywheel lump?
Yes yes! Surely.
But since I filed the flywheel hump on Saturday, I haven't actually tested yet, have been waiting for new gasket for the carbs. It should come in today, so I'll test it out when I get home, hopefully. I do have micrometer, I'll check the needle diameter. My plan is, now I reset the timing by modifying the flywheel, I'll put the carbs back to where it was before the engine work (I know that was more or less running fine), then start from there again.
 

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Discussion Starter · #71 ·
Okay, report!
I got the gasket kit for the carbs, so I put that in, put it back together with 37.5 pilot, and so this is the first test with the flywheel lump filed off by 3.92mm. It's a massive improvement, with much smoother transition from idle-2000 to above as pulling away. Having said that, it still is a bit abrupt, and as I pull away, there's shudder, like, ga ga ga ga...just around 1800-2000rpm, it's just not really happy, and as I roll on, it gets better. If I keep it right where it shudders, so much less often, but occasionally it still pops from the carbs. It's really hard to modulate around that area, and this may be where the new diaphragms may come in. That's just around the area on throttle opening where slides start to open, and I can see that the slides vibrates before it starts to open smoothly. I'm waiting for the new diaphragm, so that's one of the next experiments.
I did check the diameters of different needles, and Y271 and Factory Pro needles were exactly the same at right below the clips. The Dynojet needles were about .05mm smaller. Y271 needle has a pretty shallow taper with abrupt tip, the Factory Pro and Dynojet needles are pretty similar in profile, but Dynojet has a tip that has very small added straight(-ish) addition while Factory Pro's ends at the end of the taper, as I'd normally expect. I should have put the Dynojet needle as that was what was in the carbs before the engine work, but I totally forgot about it today.
At least I may be able to properly ride it tomorrow as is.
 

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Do them as many times as l have and you will get really fast at it.
 

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Keep the fatter needles (factory would be my choice though i have measured them as smaller than oem in the past) in for now . remember richer was worse.
Have you ridden the bike much before the teardown?
What condition are the clutch plates? If you have steels with high spots they will not allow you to smoothly slip the clutch away but will chatter on release. Obvoiusly this has nothing to do with popping in the carbs but still may be part of the problem.
 

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Discussion Starter · #75 ·
Keep the fatter needles (factory would be my choice though i have measured them as smaller than oem in the past) in for now . remember richer was worse.
Have you ridden the bike much before the teardown?
What condition are the clutch plates? If you have steels with high spots they will not allow you to smoothly slip the clutch away but will chatter on release. Obvoiusly this has nothing to do with popping in the carbs but still may be part of the problem.
Yeah, I rode it regularly before taking it off the road. It never was particularly smooth at the get-away, but it just never was that bad. The clutch is an interesting thought. It did sit for a good 7 months, so I'll have a look at that, too. I didn't get to ride this morning, so hoping that I have time this evening to take it for a quick runabout, so I have better idea of what's what.
 

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J.B. I had the same issue on a 1994 Monster M900 with a stage 2 DynoJet kit on the original Mikunis. I am not saying that the underlying problem is the same, that's unlikely, but I wanted to share my experience in case it helps. The way you described it: "Having said that, it still is a bit abrupt, and as I pull away, there's shudder, like, ga ga ga ga...just around 1800-2000rpm, it's just not really happy, and as I roll on, it gets better", is the best description I have ever read of the issue I used to have.

I tried pretty much everything to fix it, cleaned up the carbs multiple times, tried adjusting the main jet clip, replaced O-rings, balanced bodies, adjusted mixture screws by using a CO sensor, nothing helped. In the end the fix was rather trivial: the carbs couldn't breathe unless I opened the airbox (yes, I had made the mistake of putting back the original closed airbox). With an open airbox (I cut a spare one myself, and saved the original Cagiva one) and a K&N high flow filter, the issue is 99% gone.

Again, you probably already have an open airbox and this won't help much, but I just thought I'd share my experience.
 

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Discussion Starter · #77 ·
J.B. I had the same issue on a 1994 Monster M900 with a stage 2 DynoJet kit on the original Mikunis. I am not saying that the underlying problem is the same, that's unlikely, but I wanted to share my experience in case it helps. The way you described it: "Having said that, it still is a bit abrupt, and as I pull away, there's shudder, like, ga ga ga ga...just around 1800-2000rpm, it's just not really happy, and as I roll on, it gets better", is the best description I have ever read of the issue I used to have.

I tried pretty much everything to fix it, cleaned up the carbs multiple times, tried adjusting the main jet clip, replaced O-rings, balanced bodies, adjusted mixture screws by using a CO sensor, nothing helped. In the end the fix was rather trivial: the carbs couldn't breathe unless I opened the airbox (yes, I had made the mistake of putting back the original closed airbox). With an open airbox (I cut a spare one myself, and saved the original Cagiva one) and a K&N high flow filter, the issue is 99% gone.

Again, you probably already have an open airbox and this won't help much, but I just thought I'd share my experience.
Hey, thanks for sharing. I actually run the stock airbox cover with snorkels still on it. I have another lid that is cut open, also came with the bike. I just never used it before, I will try that as well.
 

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I’m not sure the stock filter and air box could cause an issue, mine runs very well and I have a K&N element and swiss cheesed lid. Stock air box is pretty large internal volume and the area of the filter is also good. Small volume in the air box or small filtration area can be an issue, or filter too close to the carburetor. The SS is pretty good, but you never know. Bigger the better.
 

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Per belters post, I’ve seen clutch issues where the whole frigging basket was moving around when you pulled the lever. Not going to work right if that happens.
 
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