rich running

[themoudie]

Morning Alex,

Ducati factory carburettor set up for the 1974 250 MKIII 1970-74 model (Blue/Gold colour scheme):

Dellorto VHB29 AD (29mm)

Needle = V13
Main jet = 110
Pilot jet = 40
Slide = 40
Needle clip position = 2 groove from the top of the needle
Needle jet = 265M

The only difference between the 250cc and 350cc 1970 - 74 models carb set up, appears to be the Main jet that is changed to a 115 on the 350cc engine.

The 450's from the same period, whilst using the same carb body, use a completely different set of internal components.

Good health, Bill

[LaceyDucati]

Alex

Checking /setting the ignition with the AAU locked in advance is a good theory, but unfortunately many of the AAU's have more than the 28 degrees advance as specified. Therefore often the resulting static timing is too far retarded to start well, that said at 36 degrees BTDC you should be in with a chance. If two different carbs and 2 different ignitions give the same lack of ability to rev and no real change then Maybe time to look else where...

Firstly cam timing - I have found a few late Mark 3's to have the cam bevel dot one tooth out for correct factory timing, so have you checked the cam timing?

Secondly - what silencer is fitted, some aftermarket replica silentiums of the 90's were very restrictive.

Just a few thoughts...

Nigel

[Scottish888]

Thanks to all for your thoughtful advice.
As Nigel says it may be something beyons carb and ignition.
Today the bike started first time with the original ducati electronic ign and Dellorto carb, filling up that part in the carb body worked.
Took it out for a ride and it still wont rev beyond 6k ish as I thought.
Back home started up the bike, ticking over and began to adjust the stator plate (mid point on the adjustment slot was best) until the engine was running faster and smoother. it was in the mid position. set the revs to 3000 and done the same, advancing and retarding as it was running, it was smoothest and better at that same mid point of adjustment.
Revved the engine as high as it would go and no amount of stator adjustment got it reving higher or cleaner, if too much adv or retard it affected it but mid point was as good as I could set it.
Tightened up the screws and it starts and runs fine.
I was impressed that no matter where the stator was set, the engine kept running, roughly at the extremes but still kept running. Got to say that electronic ign seems a lot more flexible than the points setup, quite impressed.
So, it looks like the ignition is not the issue, I gave it full adv and retard when running at tickover 3k and max (6k + at the moment)
I was going to lowere the needle on the Dellorto but seen the settings from Bill and mine is in the middle. The plug was black but then all that revving and low revs are not a good test, just clutching at straws to find the magic fix so i'll leave the carb and ign as is for now.
Nigel, the silencer markings are Silentium, Moto Ducati 1984. It has three screws to remove the baffle but its likely rusted in place. I could try running it on the front pipe only..have to consider my neighbours so not easy.
The bike starts easily and runs smoothly till that upper rev range.
When I rebuilt the engine, I thought I was super careful with all the cam timing and setting the drive pinion mesh/backlash, All the dots line up as they should. I followed all the expert advice on this forum.
But I have to look again, if all the dots/marks line up, what else can be done?

Regards

[Duccout]

Alex,

As long as you have a timing disc that you can attach to the crankshaft, it is pretty easy to do a quick check on the valve timing. I set my 250 up using the timing dots, and it ran perfectly well, but when I checked with a timing disc it was one tooth out. As long as you know what camshaft that you have, and the opening and closing timings, then with the rocker covers off and TDC found, you can get a fairly accurate picture. It won't be spot-on because there are errors in the grind of the lobes and the teeth of the bevel gears, but you will know that the cam is timed correctly.

It is all good fun really, think of how boring life would be if everything went smoothly!

Good luck,

Colin

[Scottish888]

Thanks Colin,
I never used a timing disc when building the engine after a new con rod kit, piston and rebore.
I think it is a std cam, I remember seeing the grind marks where the mesh was factory calibrated and thse lined up along with the dots.
I am going to check all again just now, If I remember..at tdc all the marks should line up.
I removed the silencer and fired up the bike, bouncing between 6-7 k, bit popping but nothing beyond that.

Regards

[Scottish888]

Is this cam timing out?
Photos taken at tdc by viewing the piston and using a tdc timing wheel.
The dots line up but it is all pointing slightly right of centre if you can tell what I mean by the photos.
If I set the two dots and the cam slot (vertical to the top cover thread)) exactly centre then the timing wheel reads about 20deg after tdc
I took from two angles so you can view easier.
I have misplaced all my Ducati special tools including the cam lock tool so that may take a while to find.
Does this look ok or do I need to strip it down to the lower pinion gear and begin again?

Regards,
Alex

dcam1.jpg

dcam2.jpg

[Geordie]

Erecting a 90 degree line from the mouth of the casting, through the centre of the shaft bevel lands on the valley to the left of the marked timing tooth. That suggests it is necessary to turn the shaft bevel half a tooth anticlockwise to hit TDC. Assuming photos don't lie.

[LaceyDucati]

Alex
The only way to check the valve timing is to mount a degree disc on the end of the crank and check whether the valves are opening and closing at the correct time as per the manual. It's not always that precise (optimistically +/- 5 degrees in the manual), however one tooth out will be obvious. The point being the dots although being lined up, are sometimes (not often) out. The procedure for fitting and setting a timing disc has been cover on other threads on this forum. The Mark 3 should have a grey cam and is checked by opening the valve clearance up 0.1mm larger than the running clearance and then using a 0.1mm feeler gauge to detect valve opening and closing points. Again not the most precise method, due to the slow acceleration at that point of the cam, but it should identify the correct mesh of the gears, i.e whether the dots are all marked up correctly.

Regards Nigel

[Scottish888]

I can't find valve opening times in the Haynes manual, found a few online but most seem to be about the 350s and green/white cams.
It does look like it is half a tooth out but you can only adjust by a tooth so it would be out one way or the other.
I can fit a timing wheel ok, I use the line on the oval cover as it is very close to the edge of my timing wheel. I can use any mark as TDC as long as I note what it is and count from there.
I'm hoping the cam is out as that would be an end to the troubles, horrible to have to strip the pinions out again, I spent ages shimming them up.
I remember fitting the cam in the head on the bench using my cam lock tool, I fitted the head and drive shaft in one piece. I never had a timing wheel at that time to check so it could be out.
Regards

[Duccout]

Alex,

Here is the timing figures for the grey cam:

Inlet opens 62 deg before tdc, closes 76 deg after bdc
Exhaust opens 70 before bdc, closes 48 after tdc.

Colin