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Discussion Starter · #1 ·
do i need to split them? Can i just submerge in cleaner as is? simple green? I put the bowls in Pine Sol and they came out nice- mistakenly put the throttle cable holder in and it removed the coating.... Should i be getting an ultrasonic cleaner?
 

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I see far more issues from people taking things apart more than they need to. I would just clean them carefully as you have them now and be sure to get as much of the internal passages flowing carb cleaner/air as possible.

Ultrasonic cleaners are nice but they are no magic bullet and considering how the carbs look now in your picture might not help much more. If you were doing a bunch of carbs then YES buy an ultrasonic cleaner and learn how to use it. If not then I think you are doing just fine the way you are. Keep in mind some chemicals may attack o-rings etc and may force you to split them later. Use small soft brushes and keep the harsh chemicals to where you need it rather than everywhere.
 

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Don’t soak the diaphragms in anything other than soapy water. Pay particular attention to the low speed circuit, make sure it’s clean all the way to the tiny hole behind the slide in the venturi. Wear goggles if you use spray carb cleaner.
 

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Discussion Starter · #4 ·
Don’t soak the diaphragms in anything other than soapy water. Pay particular attention to the low speed circuit, make sure it’s clean all the way to the tiny hole behind the slide in the venturi. Wear goggles if you use spray carb cleaner.
copy that- forgive my ignorance- which is the low speed circuit? Also- the manual says to remove this air cut off valve- i can get one off without splitting
 

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Discussion Starter · #5 ·
I see far more issues from people taking things apart more than they need to. I would just clean them carefully as you have them now and be sure to get as much of the internal passages flowing carb cleaner/air as possible.

Ultrasonic cleaners are nice but they are no magic bullet and considering how the carbs look now in your picture might not help much more. If you were doing a bunch of carbs then YES buy an ultrasonic cleaner and learn how to use it. If not then I think you are doing just fine the way you are. Keep in mind some chemicals may attack o-rings etc and may force you to split them later. Use small soft brushes and keep the harsh chemicals to where you need it rather than everywhere.


Got it thanks!
 

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Discussion Starter · #6 ·
I see far more issues from people taking things apart more than they need to. I would just clean them carefully as you have them now and be sure to get as much of the internal passages flowing carb cleaner/air as possible.

Ultrasonic cleaners are nice but they are no magic bullet and considering how the carbs look now in your picture might not help much more. If you were doing a bunch of carbs then YES buy an ultrasonic cleaner and learn how to use it. If not then I think you are doing just fine the way you are. Keep in mind some chemicals may attack o-rings etc and may force you to split them later. Use small soft brushes and keep the harsh chemicals to where you need it rather than everywhere.

also- is this the emulsion tube? Looks very round to me I've read it can get worn- oval shaped - this looks ok?
 

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using an old style oil can to pump oil through the holes is a great way to really clean them out. works better than anything else ime.

needle jets wear at the top where the needle goes in and out. can be hard to see. if it was making the plugs black at all, replace them.

there is a little o-ring on the white plastic piece that the needle jet goes through. you can't buy them from duacti, they're 10x1.5. replace them too.

the overrun valves are up to you, i'd not bother unless the carbs were really crappy.
 

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I would remove the needle jet and then place a needle inside. With the fat part of the needle filling the needle jet at the top of the hole(not the shield but where it is still a full circle. Look for any out of round. Any aftermarket needles such as you have are prone to eroding the jet when at high needle positions so they often wear into a teardrop size. A small amount of wear will bleed extra fuel past when the slide is mostly closed so it has a big effect. If in doubt change them, size of jet is on the size Y-2 Y-4 etc. Be sure to get supersport 900 jets as other models use different sizes.

I would NOT remove the anti backfire diaphragms as I do not believe there has ever been a need to. I will guess you have LT Snyders book that you are reading from, I have yet to find a set of carbs in 20 years of doing this where this was an issue.
 

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Discussion Starter · #9 ·
I would remove the needle jet and then place a needle inside. With the fat part of the needle filling the needle jet at the top of the hole(not the shield but where it is still a full circle. Look for any out of round. Any aftermarket needles such as you have are prone to eroding the jet when at high needle positions so they often wear into a teardrop size. A small amount of wear will bleed extra fuel past when the slide is mostly closed so it has a big effect. If in doubt change them, size of jet is on the size Y-2 Y-4 etc. Be sure to get supersport 900 jets as other models use different sizes.

I would NOT remove the anti backfire diaphragms as I do not believe there has ever been a need to. I will guess you have LT Snyders book that you are reading from, I have yet to find a set of carbs in 20 years of doing this where this was an issue.
They seemed nice and round using the technique you mentioned- upon reassembly- i noticed i don't have the washer mentioned here in Haynes???? Hmmm. Do i need it?
 

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I do find these carbs missing this washer enough I stock them after stealing them from about every set I had lying around. I do believe there may have been a jet kit (or misreading of) that eliminated this washer. Deleting or adding it will alter needle height so Adjust your clip position if you add it.

If you look in the slide you will see a step inside there the washer seats, without it the plastic piece under the needle clip sets on this section of shelf. If you notice the needle naturally cants when installed this is why, the shim does not stop this but it gives the plastic bit on the needle a full seat to set on.

FYI I just looked the piece is ducati part 13440071a and it is
11mm Od
5mm Id
.5mm thick

Nothing that special about it that a pair of shims of slightly different dimensions would not work as long as you compensate for the thickness in your needle position.
 

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the washer is 0.5mm, or half a clip change.

needle jets:

3240041a is y-2, 900ss, 600m, later 750
13240041b is y-6, 600ss and 750ss
13240041c dunno,
13240041d is y-4 or y-8 it seems, 400ss and 750m '96-'97 both use the part number for different spec'd jets.
13240041e is y-0, cagiva elephant

never seen cleaning or replacing the overrun valves give any change. wonder if blocking them on a city bike would help economy? we got told the low speed richness was due to the leaking before we worked out it was the needle jets.
 

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I do find these carbs missing this washer enough I stock them after stealing them from about every set I had lying around. I do believe there may have been a jet kit (or misreading of) that eliminated this washer. Deleting or adding it will alter needle height so Adjust your clip position if you add it.

If you look in the slide you will see a step inside there the washer seats, without it the plastic piece under the needle clip sets on this section of shelf. If you notice the needle naturally cants when installed this is why, the shim does not stop this but it gives the plastic bit on the needle a full seat to set on.

FYI I just looked the piece is ducati part 13440071a and it is
11mm Od
5mm Id
.5mm thick

Nothing that special about it that a pair of shims of slightly different dimensions would not work as long as you compensate for the thickness in your needle position.
@ducvet......could the resultant canting of the needle preload the needle to needle jet clearance through some of its travel, thereby attributing to or enhancing the ovaling process? Thoughts?

What is the actual reason for the "step" in the needle mount base in the slide, causing the canting in the first place?

Pic: I happen to have a slide apart, notice the needle angle due to the seat design. Yes, the needle is assembled correctly, with the 11mm, .5mm thick oem washer installed. I've never seen another needle arrangement other than straight and true exit from a slide. I can't understand, nor see a valid reason why Mikuni would allow to let this go?

And thanking you in advance, your experience and knowledge fully respected here.

@bradblack....you too! very helpful
 

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could the resultant canting of the needle preload the needle to needle jet clearance through some of its travel, thereby attributing to or enhancing the ovaling process?
I would think it would wear a little faster but the versions without the step in the slide still wear needles the same way. I have two slides in my hand one with and one (early) without, I find it hard to believe Mikuni did not want to have the needle under tension for a reason because the slide would be a revision on one they already had and cost them more money to add the step in the bottom.

Since I was not in on the research all I can do is guess so take it for what it is worth. If you have a needle floating then as it rises and falls the needle will get smaller giving it more room to walk around in the needle jet, preloading it to one side may keep the needle from jumping all around. The question is were they doing this from a reliability standpoint to keep needles from breaking or wearing the needle jets more. Or was it because the more stable needle allows the fuel to exit the needle jet without a needle that is jumping all over the place.

I doubt it was due to breaking needles as I never see those so I would guess it was either for better wear or better fuel /air flow.
 

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I’ve seen other carbs where the needle is deliberately canted and I believe the idea behind it is that the air flow is supposed to center the needle. I assume they did the testing to back that up. Personally I would think it would contribute to needle and emulsion tube wear, but I leave it as designed.
 

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i dunno...in stock form the needle is already canted (and preloaded) towards the intake side...with obvious "interference". Now add some airflow.....wear would be fully understandable.

Understandable needle stability may have been the motive, but at the expense of its jet?

Factory Pro has documented wear in as little as 5000 miles, hence their nickle plated version, which is evidently NLA.

Thinking on this further. Thanks to you both for thoughts and comments.
 

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The factory needles are rougher in texture than dynojet jets, think more like a steak knife than smooth blade. You can feel this if you run your nails or teeth down them. Needle jets are replaceable and normally last for many thousands of miles, if you want maximum miles from them I suggest M750 adjustable stock needles. Late model M750 had them and they are stock profile but can be raised via multiple positions. This gives less fuel at WOT but for driveability they are fine and the telephone pole profile means they will wear very little on the needle jets.

Hey it could be worse some carbs do not have replaceable needle jets so when worn you need a new set or a machinist. There is no free lunch something had to be sacrificial and mikuni chose the needle jets, otherwise we would be likely changing worn needles.
 
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