Dual carb confusion

[pwthom]

To anyone listening and helpful,

New to wrenching Ducatis, or anything with more than one carb.  Recently purchashed a 99 M750 that had been sitting for a year (according to PO).  Replaced the battery and completely cleaned and rebuilt (gaskets) carbs and changed oil and filter.  Front cyl is running very hot (rear cyl seems normal temp and plug is clean), but the brand new plug (NGK) is black and sooty (but not wet).  This is counter to my experience/knowledge.  I have fiddled with idle per my experience and played with the synch (per what, intuition?)  Also, I have found no apparent vacuum leaks.

My confusion is in the hot cyl with black plug.  Any hypotheses?

Also, PO said that timing and valves were done approx 6k ago, and a timing light tells me that the timing is erratic (synching?), but not SO far off.  I guess anyone would want to know that the bike reads 21k on mileage, and the PO asserts regular maintenance (though no records).

Thoughts?

Anyone?

[brad black]

how do you know it's running hot?

[the_Journeyman]

Yes, give a little more info on how it's hot.  I've got a '99 M750 with nearly 40,000 miles.  Did you do the carb cleaning or the PO?  It's entirely possible despite the carb rebuild, something was missed like a partially clogged jet or something. 

JM

[pwthom]

I completely disassembled the carbs and soaked the parts in Chem-Dip then blew air through all passages.  The bike will start and idle on choke, and will run off choke with throttle but will die as soon as the throttle is off.  Fiddling with the idle and synch seem to have no effect on the idle off choke, but do with it on.  Also, adjusting the pilots seems to have no effect.

The front cyl is considerably hotter to the touch than the rear.

[the_Journeyman]

Honestly, that sounds like a pilot circuit issue.  When you say adjusting the pilots, are you meaning the pilot screws or the jets?

JM

[pwthom]

I mean the pilot screws.

My next move is to pull the carbs and clean everything AGAIN.

[pwthom]

Also, any thoughts on the mixed signals?

[ducpainter]

You say you fiddled with the synch screw.

Did you use gauges?

[pwthom]

Not yet.  I have a vacuum gauge, but I played it by ear, listening for a dulcet and consistent rattle.

Per this writing, I have cleaned the carbs again and it will now hold an idle, but with a little pop here and there.  Apparantly I neglected the slow jet somehow.  Also, and according to what I understand from this forum as normal, the idle holds fast for a short time after blipping the throttle.  I am still finnesing the idle and pilots, so this does not worry me.  As of now, I am calling this some success, albeit at the expense of my humility.

I still plan to re-jet, as I know that factory settings are fairly lean and the after-market tends to smooth things out.  On that note, is there a real difference or preference among the makers, i.e Dyno v. Factory Pro?  I have always had good luck with Dyno, but I thought that I'd ask.

[alibaba]

The Journey_Man is right on.  Aside from whatever other problems you may have, if the pilot air screws are not making a difference, then you have pilot circuit problems.  This is the most common problem with carburetors.  Especially if they have sat a while.
I can't tell you how many times I have heard folks swear that they cleaned the pilot circuit only for it to fail the test.  Squirt some WD40 into the pilot passage in the mouth of the carb.  If you can't see two 'fountains" shooting up from the floor of the carb, you have found your problem. 

Use carb cleaner, compressed air and (carfully) small wires to clean passageways.
I have yet to find a modern carb cleaner that actually works well since they EPA'd" the good stuff that would eat its own container after a while.  ;-)

And remember, all carb troubleshooting starts with setting the float height correctly.

[ducpainter]

Not yet.  I have a vacuum gauge, but I played it by ear, listening for a dulcet and consistent rattle.

Per this writing, I have cleaned the carbs again and it will now hold an idle, but with a little pop here and there.  Apparantly I neglected the slow jet somehow.  Also, and according to what I understand from this forum as normal, the idle holds fast for a short time after blipping the throttle.  I am still finnesing the idle and pilots, so this does not worry me.  As of now, I am calling this some success, albeit at the expense of my humility.

I still plan to re-jet, as I know that factory settings are fairly lean and the after-market tends to smooth things out.  On that note, is there a real difference or preference among the makers, i.e Dyno v. Factory Pro?  I have always had good luck with Dyno, but I thought that I'd ask.

Idle hanging is not normal. It indicates carbs that are out of synch, or idle speed too high.

I'd recommend actually synching the carbs with a gauge before you chase windmills.