rich running

[Scottish888]

Thanks Colin

[Duccout]

To add a bit of realism and humour, I will relate a tale: many years ago, when I had my beloved 750 Ducati, I had managed to accumulate four different camshafts, so I thought that it would be good to discover which of them would be best to use, so I rigged up a dial gauge on the valve stems and a degree disc on the crank and took the timing figures for all four cams. The result was that all four cams gave different timings, all across the range, and not even in a way that would have been fixable by moving the bevel gears forward or back - some cams opened early and closed late, and some opened late and closed early, and the lift figures varied wildly at the same timing.

No wonder Anthony Ainslie told me that tuning a 750 won't make it go any faster because the timings are so different on each cylinder.

It reminds me of the old Manx Norton tuners, who were regarded as wizards of the black art.

Colin

[Scottish888]

my figures seem weird but so far this is what I find
inlet open 66-67 btdc
inlet close 79-80 abdc
Ex open 71-72 bbdc
Ex close 58-59 atdc
The ex close is 10 deg out compared to the 48 quoted.
How can that be so far out but the others are only 2 or 3 deg out?
I am using a .0015 feeler guage and recording as soon I feel tension or release, making sure the reading is taken with the engine turning the correct way after rocking back and forth a bit.
Going to check all again as it is likely I am getting this wrong but If the figures are repeatable how many degrees does one tooth equal or is 2 or 3 deg not able to adjust out?

Regards

[LaceyDucati]

Alex
Bearing in mind all the inaccuracies of this form of checking, Ducati's variations and potential for wear in the coupling etc that can skew the readings, I would say those figures are within normality as far as these bikes are concerned. I was looking for all the figures being skewed maybe 17 degrees or so, I would deduce that your cam is probably the original Grey cam set probably as right as it can be. I've seen Desmo cams far later shutting than that on the exhaust, some 25 degrees from spec or 40 from your reading!! So unfortunate another dead end, but another thing to almost certainly discount.

Moving on, my guess is your silencer is one of the restrictive ones, have you another more generic silencer (preferably more straight through) from something else that you could try to rule that out too?

Regards Nigel

[Scottish888]

Thanks Nigel,

Thanks for reassuring me the cam numbers are ok, Just confirmed the figures are the same as my last test.
Yesterday I removed the silencer and run it on the front pipe, would not go beyond 6-7k.
Obviously something wrong somewhere but I can't think of anything else to try, first time I have been defeated and confounded by a bike (or car)
It could be that both ignition systems are dodgy but strangely produce the same fault, 3 carbs, two of which were new (mikuni vm30 and an OKO) the original had an overhaul kit all three produce the same fault.
Valve timing seems within limits, removing the silencer helped it rev a little higher but not much.
End of story, will just have to use it under 5 k as it is perfect till then.
Thanks everyone for the advice, I wish I could have found the issue as others could benefit from such a comprehensive fault check list.

[Duccout]

Alex,

A quick recollection from 'Bike' magazine's road test of a 250 Mk111 about 1975, (and I think that I'm remembering this correctly) where the bike would not rev and it was found to have the ignition timing out and was fitted with an incorrect main jet. Have you tried a bigger (or smaller) main jet in the Dell'Orto? I'm guessing that you would have, but I thought I'd mention it as running better when the throttle is closed slightly is classic weakness.

BTW, 'Bike's 250 Mk111 turned out to be the fastest of all eight 250's on test, recording 92 MPH.

Colin

[Scottish888]

I have a copy of that magazine somewhere
I checked the carb jets this eve against the specs kindly given by Bill earlier and found that two were 350 spec, the main jet was a 115 and the pilot a 50 so Ive put the needle clip in the top notch to weaken it a bit.
All the other parts were the same as a 250 should be. I'll get the proper jets and try again.
The bike started easily and run up to 6k easy enough, going for 7k resulted in some popping and not much else.
I'm going to try running the bike for a couple of hours and see how it goes.
Thanks for all the advice

[Duccout]

Possibly, not revving is a common problem? I don't know, but I had a 450 Mk111 that did not rev (which Iput down to the camshaft) and 'Motorcycle Sport' had a touring article about a 450 Mk111 that would not pull past 70 MPH in top, and then there was the 'Bike' test of the 250 Mk111.......

Colin

[LaceyDucati]

My solution would be to change everything you can at the same time, as it's quicker and you may well have more than one issue. That would be open silencer (tested on the road) the alternative carb (with plug readings to obtain suitable main jet) no filter (for test purposes) and a new known ignition. The new carb should allow the engine to rev if the main is correct even if it's all over the place elsewhere, that can be sorted later. There has always been a question mark over used some old VHB's on Ducati singles, even if some work well and generally VHB's seem to work fine on Guzzi's etc. The silencer is probably less that ideal for top end with the grey cam. If you get it reving then you can introduce everything back one at a time I.e. carb, filter, silencer etc.

Frustrating as it is, there is obviously an issue....My experience of my Mark 3 as a 250 and lately a 350 is it will rev very freely round to 9000 rpm as a 250 or 8000rpm as a 350 with ease through the gears. Then again I have never used original carbs, silencers or ignition.

Good luck with it

Regards Nigel

[LaceyDucati]

Just a final thought, is the fuel supply okay, no crap in the tank, breather issues etc. I would have thought that would be more abrupt, die completly and take awhile to clear rather than just popping a bit and hitting a wall as such. just a thought.

Nigel