non starting 250

I’m trying to find out how to get a Ducati single to start running again. Fuel in tank, taps open, 12.5V in the battery, plug sparking outside the cylinder, smell of petrol from the cylinder. Kicks over but won’t fire up. Puzzled!

Worked before- generally starting first or second kick with about one third choke- but I have left it for a couple of months and no joy now. Recently took the carb apart- a Dellorto- cleaned it all out and put it back together with new seals. Seemed to run better after that, pulling better above 4000rpm.

Generally was running rich. Does anyone know which way to turn the mixture screw to lean it? Clockwise gives 4 turns until it’s all the way in. but is in or out richer or leaner? and does too rich prevent an engine starting?

Push starting doesn’t work either.

Am I missing something terribly obvious?


A few ideas, some of which I’m sure you’ve tried …

  1. Fit a new plug (and clean the plug lead and make sure it’s fitting into the coil well).

  2. Check the carb control cables, i.e. make sure that neither the enricher nor the slide is hanging up.

  3. Did you re-set the float height? If too high, you can have trouble starting.

  4. If you have a PHF carb, it is important that the drilling which provides air for the idle circuit is clear - with today’s fuels, it often gets blocked as the lighter elements in the fuel evaporates. Then the bike won’t start. I’ve had this happen in 6 weeks of non-use on my Laverda Corsa. Carb cleaner can help, ultrasonic bath is best.

  5. Strictly speaking, the idle screw doesn’t either weaken or enrichen. Instead, it adjusts the amount of air/fuel mixture, with the mixture strength being pre-determined - see the Dell’Orto manual posted here

But that said: out is more mixture, in is less. I½ turns out should be your starting point.

  1. Did the bike idle before?

Btw, in general, the ‘choke’ (it’s not a choke, but I’m sure you know this) should be either on or off - in fact, the later twins used just such a control.



Dear Craig

I wouldn’t be too sure that I’ve tried any of these!

  1. New plug, yes Swapped to an iridium plug, no7, and it works brilliantly- for a short time.
  2. Check the carb control cables- Hadn’t thought of that!
  3. Did you re-set the float height? Hadn’t thought of that either.
  4. PHF carb? No idea, I thought I have a VHB 29 AD. I’d better look at your file to find out where this drilling is. Have hosed the whole thing down with masses of xylene(?) spray earlier in the Summer. Bob Hartmann has offered to ultrasonically clean it for me, should I need it.
  5. I½ turns out should be your starting point. Tried that last time I was out- masses of backfires and won’t pull at all.
  6. Did the bike idle before? Yes, but it wouldn’t pull above about 4000 rpm, which is why I took it apart and cleaned it all out.
    Btw, in general, the ‘choke’ (it’s not a choke, but I’m sure you know this) should be either on or off. Both this desmo and my old mk3 always started well with half choke- or whatever the lever on the left handlebar is.

The consensus in London seems to be that I may have a worn float needle (part 29, page 65, Haynes manual) or seat, bent float ‘spring’ as the thing is obviously flooding.

Thanks for all the advice. Hope to get to work on it next weekend.


ps Following post was my query to

28 September 2008

DOCGB Singles focus group

re: desmo 250

Me again!

Is there a general forum where I can discuss these problems, or should I just email to you? You seem to be taking on an enormous burden if you’re dealing with this sort of stuff all on your own.

Swapped to an iridium plug, no7, and it works brilliantly- for a short time.

Left it standing for 2 weeks. Came back yesterday, tried to kickstart, kickstart won’t budge! Took the plug out to have a look. Strong smell of petrol. tried the kickstart by hand to look for a spark. The kickstart works but petrol is hurled out of the plug hole( not very technical ). A few more hand kickstarts and all the petrol is out. Plug back in- brilliant fires straight away and runs fine. Out for a spin in the brilliant weather of North Kent. Absolutely brilliant. I have discovered that I can finally remember how to get round corners gracefully.

Today it starts fine and off I go, but is soon misfiring and won’t idle. Fiddled with the carb (Dell 'Orto) and got it to idle- about 2 turns out on the throttle stop screw and 1.5 screws out on the mixture screw. Won’t rev at all and backfires a huge amount, but got me home. Found the headlight is very, very dull. Could it be not charging and a flat battery is affecting the electronic ignition? It won’t start with a flat battery, I have discovered every Spring. Battery out and discovered it is holding 11.5V. Not wonderful but surely enough?

Cleaned the carb out a month or so ago.

Battery was new this Spring.

I did wire the battery in back to front and fried the 2 main leads, but it’s been working fine since then and positively well since I cleaned the carb.

Any ideas?

Any advice on good single cylinder carb-tuning mechanics in the Bromley area?


  1. If you couldn’t turn the engine over, and then there was fuel coming out of the plug hole, it sounds like you had what is called ‘hydraulic lock’, i.e. so much fuel had leaked into the combustion chamber that the piston couldn’t move.

This is caused by the float valve not sealing, allowing fuel to fill the float bowl and then flood the combustion chamber. And this could also explain some of your other problems, too.

Try renewing both the valve and needle, and also re-set the float valve height. I think this is 24mm for a VHB, but best check with Eurocarb when you buy the float valve assembly.

(Also, remember to turn the fuel tap(s) off when the bike is standing - and make sure they work, too!)

You should also check that fuel hasn’t got past the piston and into the oil and diluted it - if it has, you can normally smell the petrol when you take the dipstick out.

  1. You say your bike has electronic ignition. Is this the Ducati one, or an after-market system? I believe the Boyer can be sensitive to battery condition.

  2. If you want help locally, contact Chris Bushell, 01959-522249. He’s in Otford, near Sevenoaks.



Chris Bushall is almost…No It is swearing on this forum.
After attemping to take control of this club he left and set up his own club the DSC.
Then set about undermining this club at almost every oppertunity, even setting up/registering web site address’s similar to this sites to harvest off potential members…
Some on here would consider him the Antichrist, I wouldn’t go that far but I’d go VERY close!
This club (The DOC GB) was all the better for him leaving IMO.
The Com of this club would probably ask me to tone this down, but I think it not only needs to be said but should be said, in fact I’m moved to poetry so here goes…

What kind of a creature begat him?
Was it some kind of a Bat?
They can’t think of a name for him,
But I can…

John Cooper Clark.

C B’s own club have been trying to remove him for some years now, his antics have brought that club to it’s knees.
Any DSC club member who questions the leadership pretty quickly gets banned/frozen out from the club.
This has resulted in the DSC splitting into a few new factions/internet clubs.
There I’ve said what needs to be said and I WON’T withdraw it.

Steve R

Hi Ignatz, These motors can be very fussy over spark plugs, Once they oil up internaly its best to try a new one. I have a 250 and bump start more often than not. Fresh fuel , fresh plug, clean points and it should go, What have you worked on since it last ran? .The previous owner of mine built in so many problems it has taken years to sort out. I also live in Bromley and am willing to give you help. I have converted to 12volts and have an ignition booster(Pazon) fitted so even dirty points dont phaze it.

A battery voltage 11+ is not good under load it will drop lower, sounds like the charge is out, plus a float that is sticking, IF you are on standard carb settup its also likely to run rich on current gas.Mine would not rev past 55 or 6 till i reduced the main .Try a 6 plug while fault finding , it may not foul so quick but too soft for normal use.Backfiring can be intermitent ignition. Thats a full house!! take your pick.