Del-orto carbs, help needed please

Hello chaps.

Do we have a carb specialist in the club, or one someone can recommend ?

I have a 1980 V50 mk 2.

This bike hadn’t been ridden since October 1986, and had been left with fuel in it.

The carbs were solid, I removed the fuel varnish by using marine clean, then ultra sonically cleaning the shells, I then fitted new jets, needles, washers, gaskets etc.

I set the carbs up as per the manual, and used a colour tune kit to set the mixture on tickover, all ok so far.

The problem I have is as soon as you lift the needle, both cylinders go rich, very rich, white on the colour tune, I have dropped the needles to their lowest position, but still no improvement.

I’m no mechanical engineer, and I’m now lost, so who can anyone suggest please ?

A couple of ideas;
There have been a few threads on carb issues so a tech section search may be worthwhile,
there’s also a link to the carb manuals too. May be useful in checking he assembly details
All the bet

Are you using standard air filters or K & N type?

Standard everything, except I have now fitted some iridium spark plugs.

Not sure if this helps but I tried Iridium plugs on my 1980 Ducati and it never ran well with them and starting was a pig. Went back to standard NGK’s and never looked back.

I thought that a rich mixture showed up orange on the Colourtune. White is too weak surely?


just got my gunsen book out we have
yellow to rich
bunsen blue all correct
whitish blue lean to weak
all depends on you view of colours

It’s definately rich chaps, no matter how you describe the colour, the plugs are as black as a black thing.

try disconecting the choke cables for a start and make sure the choke plungers are actually sealing on the rubbers
the choke cable needs at least 3mm of slack cable in them to make sure they do not get lifted slightly off the seats

They will be because you’ve started it from cold and probably pumped the twistgrip a bit as well. The plugs now need to burn off the soot which they won’t until a proper ride. I’ve answered this before, but correct way to go by plug colour is first to get it properly warmed up (can’t do this on the stand, has to be ridden a few miles) ride along a road, simultaneously cut the kill switch and pull the clutch, coast to a stop then pull the plugs to look at their colour. Although closing the throttle to idle and stopping normally and switch off should be practically the same. Colortune is OK for checking idle mixture ONLY. Stopped using mine years ago when I found how limited its usefulness actually was and just went by plug colour. HTH

Many thanks Mike, I realise you’re only trying to help.

The plugs are as black as a black thing, even after a run, trust me, it is as rich as hell.

I’ve either got too much petrol, or not enough air !

I can only think there’s an air gallery still blocked, the idle jet will use one to mix fuel and air, there’s a tiny pin hole downstream of the slide, that’s where the idle mixture comes out. And another one under the slide (progressive stage). But according to my Dellorto guide there should a second airway to mix with the needle jet. Maybe that’s you problem? The entrances to the air galleries are on the intake side. HTH

Thanks Mike, I think I’m going to have to start again.

I’ve been having a think this afternoon, in case you don’t know I’ve just rebuilt this, and it hadn’t run since 1986.

I’ll start by removing the carbs from the air filter, just to make sure I’ve not restricted airflow somehow, assuming that they are both still too rich, I’ll strip them, to see what I’ve got wrong, as it is both carbs, with exactly the same problem, it must be something I’ve got wrong.

Are you sure you have the correct jets everywhere? Did you renew the atomizer jets which get worn oval by the action of the needle? This will make an enormous difference just off tickover.

This does sound like something is still clagged up. What I tend to do nowadays (learnt from experience!) is squirt aerosol carb cleaner into every orifice and make sure it actually comes out of every other opening where it should come out of. In extreme cases you may have to resort to poking it with a thin copper wire.

When I bought a non run V50 it took 4 goes to clean the carbs AND the fuel filters in the tank were clogged It takes peseverance

If any use i can strip and ultra sonic clean them in carb cleaner foyou and send them back to you

That is a well worth idea Ray does a great job

Many many thanks for the offer, I’ll get back to you.

My mate & I are going to have a look later in the week to try and see what we’ve done wrong.

We’ve either been supplied with the wrong jets/needles etc, made the same mistake on both carbs (as they are both behaving in exactly the same way), or … something is blocked/restricted on the air filter side.

I have some calls to do for the next couple of days, but, hopefully on Friday, we’ll disconnect the carbs from the air filter, and see how they behave then, if they are still both rich, we’ll have to strip them again.