2000 M750 - Running Issues - Help, Please!

[Javamoose]

Ok, so, after a year of sitting I have finally fixed my peeling tank liner and leaky fuel lines and am ready to get my bike back on the road.  Of course, it's acting up.

Was going to get it inspected.  Started it up, let it warm up for 5 minutes, put it in gear and as soon as the clutch is let out, it dies.  Again and again and again.  Sitting with it idling in neutral, when I give it partial throttle, I can hear it sucking air and kind of chuffing...not smooth.

Once it is around 1/8-1/4 throttle, it smooths out.  If I give it about 1/4 throttle and let the clutch out, I can get it moving.  But, at low speeds it is surging and rough and will easily die when starting from a stop unless given a lot of throttle.  I had put on an aftermarket gas gap, but I noticed a hissing noise from the cap and when unscrewed it would whoosh - so I went back to the stock cap.  Problem persists.

What I have done to it:

Took tank off to strip and re-line coating.  
Replaced all fuel lines up to the fuel pump.
Removed vacuum petcock and replaced with large 1/4" manual petcock.  Capped the nipple on the intake that used to go to vac petcock.
Replaced fuel filter.
Brand new battery.
New exhaust.
New fuel, obviously.  

If the two vent lines on the bottom of the tank are swapped, would that cause this issue?  It seems like it is getting plenty of gas, at higher RPMs it's running very strong, better than it used to.  I checked and none of the fittings on the tank are clogged.  Vent lines inside this tank are metal, not rubber hoses - as far as I can see, they look good.  When I still had the tank off, I ran air through both lines and it came out of the vent holes by the cap just fine.  Fuel supply fitting/hole is clear and not blocked at all.

I was really hoping to get her on the road for the long weekend...but now, I don't know.  

[the_Journeyman]

I had a vacuum leak when mine was acting similar.  It didn't want to take throttle, but would if I really twisted.  I had to replace my diaphragms too, and I found a MUCH cheaper than Ducati replacement.  PM me if you get in there and find the diaphragms are bad.

JM

[Javamoose]

I had a vacuum leak when mine was acting similar.  It didn't want to take throttle, but would if I really twisted.  I had to replace my diaphragms too, and I found a MUCH cheaper than Ducati replacement.  PM me if you get in there and find the diaphragms are bad.

JM

When I removed the vac petcock, I just used a silicone cap and the stock clamp to cap the vac nipple on the intake runner.  It seemed like it was secure, and it is still there, but IF it isn't air-tight and is causing a vac leak, would that tiny little leak be enough to make it run like that?  FYI - The cap I used is McMaster part 92805K14.

Also, what diaphragms are you talking about?  The fuel pump? Carbs?

[the_Journeyman]

Carb diaphragms.

Not sure a tiny leak would cause that, but I'm not an expert on carbs.  I had several cracks in my carb diaphragms, and had pinched a wire bolting the carb tops on.  My carbs were also a bit out of synch too, and that cause the same stalling just off idle issue.

JM

[Howie]

Check throttle synch and look for vacuum leaks  before anything else.  Easiest/cheapest first. 

[Javamoose]

Carb diaphragms.

Not sure a tiny leak would cause that, but I'm not an expert on carbs.  I had several cracks in my carb diaphragms, and had pinched a wire bolting the carb tops on.  My carbs were also a bit out of synch too, and that cause the same stalling just off idle issue.

JM

Well, I hope it isn't cracked carb diaphragms.  Before the work I did on it, it ran fine (bit lean and under powered but basically fine) except when the fuel filter clogged with bits of liner.  So, it's getting a lot more gas than it was before.

Check throttle synch and look for vacuum leaks  before anything else.  Easiest/cheapest first.  

How do I check throttle sync?  Other than the one vac line I removed (went to vac petcock) and capped - all the other lines appear good, as far as I can see.  Also, I am getting pop/backfire on deceleration now - never did that before...

EDIT:  Ok, looked at the sync guide from Ducati Suite http://www.ducatisuite.com/carbsynch.html - This seems a bit...difficult.  How do I do all this while keeping the bike running, especially since when I put my kickstand down the bike shuts off?

Another question:  If I didn't have this problem before, why would it be doing it now?

[Howie]

Remove the connector on the side stand switch.  Jump the two wires.  Now the bike will star and run on the sidestand.  The diaphragms are probably OK if the bike runs well at speed.  It wouldn't hurt to check though.  An easy check is, with the air filter removed, accelerate the engine.  Watch the slides.  They should raise equally.  They won't raise much, but they will raise.  There is also another filter in system.  There is a screen in the fuel inlet at the carbs.  Unlikely this is your problem though since your bike runs at speed.

[Javamoose]

Remove the connector on the side stand switch.  Jump the two wires.  Now the bike will star and run on the sidestand. 

Ah, easy enough. 

The diaphragms are probably OK if the bike runs well at speed.  It wouldn't hurt to check though.  An easy check is, with the air filter removed, accelerate the engine.  Watch the slides.  They should raise equally.  They won't raise much, but they will raise. 

Checked.  Yes, they do raise...not much, but they do.  How equal should they be?  Does non-equal = out of sync?

There is also another filter in system.  There is a screen in the fuel inlet at the carbs.  Unlikely this is your problem though since your bike runs at speed.

Good to know, is this easy to check?

Would a video (with audio) help diagnose this?

[Howie]

Ah, easy enough.  

Checked.  Yes, they do raise...not much, but they do.  How equal should they be?  Does non-equal = out of sync?
Possibly.  Try synch first

Good to know, is this easy to check?
A pain in the ass and messy

Would a video (with audio) help diagnose this?
Wouldn't hurt.

[Javamoose]

Well, looks like I'm spending the long weekend working on this effin' thing instead of riding it... 

Local Duc dealer wanted $650 in labor alone to put new timing belts on and tune the carbs.  

Just so I can cross it off the list, if the two hoses (not the supply) got swapped when I put everything back on the tank - that wouldn't be causing this, right?

[Howie]

Doubt it.  One is a vent, the other an overflow.

[Javamoose]

When I was looking at the lines today, checking for vac leaks, I noticed that the clear Fram fuel filter still has a large pocket of air in it that I cannot seem to get rid of.  Is this normal?

[Howie]

Yes.

[Javamoose]

Hmm...so, where exactly am I supposed to connect the vac gauge to for sync'ing?  One nipple went to old vac petcock, now capped, I can hook vac gauge to that.  But, other nipple goes to the fuel pump?  Can't really disconnect that...right? 

I'm about ready to push this POS off a cliff into the ocean. 

[Howie]

Hmm...so, where exactly am I supposed to connect the vac gauge to for sync'ing?  One nipple went to old vac petcock, now capped, I can hook vac gauge to that.  But, other nipple goes to the fuel pump?  Can't really disconnect that...right? 

I'm about ready to push this POS off a cliff into the ocean. 

There were two nipples, one on each manifold foe the evap. canister.  They are either capped or replaced with 5 mm screws.