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Discussion Starter · #1 ·
Sorry for yet another topic on this subject but (I think) I've got a problem with the float height on my '97 900SS. And I can't find the answer anywhere.

I would like to check the actual fuel level inside the carbs (with the carbs mounted on the bike) with the clear-tube-to-drain-pipe method but I can't find what the height is I'm looking for when using this method...

I already know that you have to measure the level to one of the marks on the float bowl but I don't know which mark to use and how many mm I should be above or belong this mark.
I'm talking about the marks in the attached photos. Photos came from this website. Talking about the red and blue arrow. Lots of info about Yamaha there, nothing on Ducati...



Cleaned the carbs, checked everything for leaks and/or wear, set the float heights to 14mm and after re-assembling the vertical cylinder keeps running lean, even with the air-fuel screw 5 turns out. Horizontal is oké @3,5 turns out.
I suspect a problem with the float height on the vertical cylinder carb.

Before pulling the carbs again I would like to check the actual fuel height in the carbs. When I reassembled the carbs everything was checked and all seemed allright. So I think pulling the carbs again won't reveal anything new.

So, does anyone know what line I should be looking at and how many mm the level should be above or below this line?

Thanks!!!
 

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Discussion Starter · #2 ·
Just found some extra info here.

He doesn't talk about any mm above or below the Mikuni marks but it's a good start (checking the level compared to the 'dimple').

I'm gonna try this and post the result here.
I may not know how many mm I should measure but I should be able to check wether both carbs are more or less equal.

Sorry for starting this thread and finding a solution a few minutes later...
Googling "float height Ducati mikuni" didn't reveal this. I found it when using "float height clear tube drain Ducati"...

Next time I'll search a little deeper before starting another thread here...
 

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the middle of the dimple or knob. i've never seen a float level that needed adjusting. apart from ones that people have messed up by adjusting them anyway.
 

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As old as these bikes are, it’s hard to believe the float level hasn’t been “ adjusted “ by now. Float level has been blamed for all kinds of issues on this forum so most carby owners have been advised to check it. If you change the float needles you probably should check it. I usually check float level when I rebuild carbs, though if they both look pretty even and the stain inside the bowls look about right I may leave it alone. Usually I do it though , because as my boss used to say , “ If you don’t have the time to do it right, where will you find the time to do it over ?” He was an asshole, but a smart asshole.
 

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my view is that, whenever i check the fuel level, they're always ok. so i never check float level as such when i do needle jets, for instance. i don't pull the carbs off the bike either, so it's not really possible to do the float level measurement in situ, but it's something i see no value putting the time into.

i think people saying "check the float level" is a hangover from the old days and people doing stuff they "think" they should be doing (or advising). but on the oem mikunis, imo and ime, it's a waste of time. unless it's been screwed with/up before. and the fuel level test will show that up.

conversely, every time i have dellortos off and apart i check them, but they're much easier to remove and set. and they do vary a lot at times.
 

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obsessive fuel level checkout

In the course of sorting out a couple of 900ss bikes for carb problems,I checked fuel level before teardown.
Thought I'd share an upgrade to the simple 6 inch clear hose I'd always used previously .....

Note that any air bubbles in the line will throw the observed level off,
and I like to see multiple float valve seating/operations .
To do this without getting too much gas on the floor i cobbled a tubing loop with a tee and valve so that I can flush any air, and easily exercise the float function, and drain the whole thing easily.
Fuel pump on or off made no difference.
Pix are pretty self explanatory.
 

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Discussion Starter · #8 ·
I checked the float height with the clear tube method and the fuel level was spot on, both carbs.
So that means that I did a good job adjusting the float height when I was cleaning the carbs. Happy with that result.

The problem with the rear cylinder running lean is also solved.
The rubber intake manifold had some folded lips inside. This probably happened when I mounted the carbs.
So I lightly greased the inside of the manifolds and shoved the carbs in very gently.

Afterwards I balanced the carbs (with the 2-bottle-method, worked great!) and adjusted the air-fuel screw.
Bike runs smoothly now.

Lesson learned: after checking the manifolds for leaks, cracks,... be sure to be very careful when pushing the carbs in the manifold.
It was a small leak but it made the bike run like crap. Running so lean (on the vertical cylinder) that after 2 minutes of idling the rear exhaust turned red hot! And that's a sight I rather not see ever again.

Thanks for the replies!
 

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Discussion Starter · #10 ·
if the bike is stationary the headers will often glow. it's not any measure of leanness.
Ah okay, I didn't know that.
Fact is that that cylinder was actually running lean due to the leaking manifold.
I found out is was running lean by checking the sparks and the decelerating backfires I got.
When I tried syncing the carbs (no succes with a leaking manifold) I noticed the glowing header.
Only then I found out that the manifold was leaking.

Now that I fixed the leak in the manifold and adjusted the air/fuel mixture screw no headers were glowing after a few minutes of idling.
The leanness of the back cylinder probably made the header glow just a bit quicker.

But thanks for letting me know that a glowing header is no cause for panic!
 
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