monster running rough all of a sudden

[smiffyraf1]

hi guys dragged the 750 out tonight and fired up and seemed to be running real rough. started fine but just put it down to being sat with same fuel in for a while so rode down to the petrol station to get some fresh stuff. pulled fine as normal. but on overrun pops and banged a lot more than usual. got back pulled plugs and are fine, carb floats fine but there seems more oil in the airbox than normal and could see on the filter where it had been spraying up out of the carbs. no smoke though and oil level fine. i could almost swear i can hear rattling on the overrun upon pulling into the drive but on taking it straight back out without helmet to hear better could not reproduce this. i also totally lost the back brake, nothing at all felt like it had become disconnected then when got home and checked it its all fine even bled it and nothing! i dont know if ive got gremlins or someones telling me not to ride today or something but cant fathom any of it!
sorry for the essay
james

[Nickj]

The back brake sounds quite like mine, bad position being underslung as it just fills itself with crud.
I'd get the caliper off, pull the pads and clean. Then push the pistons in a little before refitting and bleeding.
Should sort i.

Rattling on over run.. funny you should mention that.....
When the bikes cold, humour me here, check the pipe from the horizontal pot isn't moving. I had something similar with the popy pop biz and what sounded at times like fuel igniting in the pipe or the chain smacking into the swing arm.
After a bit of fiddling I noticed you could flex the pipe a little, so I had the rattle and the air leak allowing some popping.
I found I was missing the exhaust washer, well there was a little left, just a small thing crescent of metal. The half washer thingys had also gone, the ones that press the pipe against the seal, not a trace of them so I bent up a set.

Oil in the airbox , not able to help there as I got pee'd off at having oil that looked like mayo at the slightest hint of mopisture in the air. I chopped most of the scavange system off. the little K&N does good. No mayo oil anymore

[smiffyraf1]

you sir, are a scholar and a gentleman
you were bob on about that front cylinder! cant believe i missed it!

[smiffyraf1]

the little half shells hadnt come out but the nuts were well loose! will strip the brake tomorrow

[utopia]

Amazing !!!
That's almost spooky.
I think we need a new forum award here, for "most feasible, yet seemingly highly unlikely, but ultimately bob on diagnosis".

[smiffyraf1]

ha ha yeah i need to take it a proper ride to confirm but on running in the garage seemed a lot better. weird that they have undone themselves and came on quite suddenly.

[utopia]

Well, I guess its an area that it subjected to massive heat cycling and pressure pulses, and the copper gaskets will harden over time too.
Its hardly surprising really, that sooner or later the joint should work fractionally loose, and once that has happened and its free to rattle around, it would deteriorate rapidly.
But fortunately the nuts weren't seized on the studs, eh ?

[smiffyraf1]

one was but unscrewed the stud instead. i cant see any copper gaskets at all. should it have some?

[smiffyraf1]

ahh i see it now

[Nickj]

The standard nuts are interesting, rather than solid they are a kind of pressed build. Still means that they split really cleanly.

[Big Daft Lad]

I was just about to post exaclty the same problem (popping), I'm off home to check mine now! I'll be sooo hapy if this is the problem.

[don_matese]

Mine was doing exactly the same thing, popping, specially on overrun and running rough. Half shells on the front were pretty much gone, nuts seized and the exhaust plate loose...took me all afternoon to chisel the nuts off and now the exhaust clamp is still stuck. Can I just shear the head off the bolt or is it threaded?

[Nickj]

HA!!! Mine was like that too.

If you've got the nuts off then the casting that pushes the half washer thingys in should be loose and just drop off (you'd think so anyway). It isn't and the casting is pulled back tight onto the studs by the down pipe position.
Go back to the junction at the rear of the engine and there ought to be a nut that holds it to the rear downpipe. Get this loosened and the front pipe will move and the clamp magically drop off.
Or if you feel really brutal get some tyre levers between the clamp and the head .. not recommended as if the half washers have corroded away then the studs might well be less than pristine where they are hidden away in the clamps and you might break one off. At least by shifting the pipe you end up with enough thread to get some nuts on and remove the studs.
BTW watch out for the parts from Ducati, I got some studs perporting to be for mine (M750) , the washers and nuts were OK but the studs were way too short. Not a problem as I used them elsewhere.

[don_matese]

Studs are ok. I've got the nuts all off and the castings off too and found the half shells but the union between the front and rear downpipes has a clamp thats corroded badly. Theres no way to get it undone. I may either chop it or drill it out so I can get the pipes off to clean them up.

[Nickj]

Oddly enough same had happened to mine too.
Hacksaw through the bold shaft got it off. Then I cleaned off the old 'fittings' for the clamp and remade the in stainless TIG'd it back up together

[jerry]

rear brakes on ducatis often boil the brake fluid due to water build up ,then the brake fails totally best to flush bleed and refill with fresh brake fluid