Carb problems

[chippit]

Just wondering if anyone can help.
I am having trouble getting my Dart to run right, I have had the carbs (VHBZ 25 BS) apart and ultrasonically cleaned them. Found the pilot jets blocked and one of the floats had petrol in it so I bought a new float and new choke 'O' rings and float height 10mm on both.
Standard air box and filter with flower pot
Main jet 92
choke 50
pilot 45
Needle height 2nd notch
For a starting point the slides are set at 1mm and mixture screw 1 1/2 turns out, it starts straight away with one choke and warms up fairly quickly, runs fine until it is warm and then starts hanging up at 3000rpm.
I have a balance pipe connecting the 2 carbs together.
Noticed on a dellorto parts diagram that there are 'O' rings and washers for the mixture screw and throttle stop screw, when I took mine apart there were no 'O' rings and washers under the springs.

Any suggestions?
Regards Christine

[John Bunting]

Hi Christine,
There should be washers and O rings on the mixture screws, Eurocarb can supply.
Regards
John

[EVguru]

Retard the ignition. It's probably 'hanging' on the advance curve. Not uncommon with the Kukusan ignition.

Do you still have a 'T' in the balance pipe leading to the air admittance valve?

[chippit]

Hi,
There is no 'T' piece just a pipe linking the 2 carbs (the air admitance valve is still in place and having taken it out to have a look does seem to work, is it worth getting a 'T' piece to reconnect it?)
I have read all the other threads about the carbs hanging up, when I have got the 'O' rings and washers I will try again. Should the Throttle stop screws have 'O' rings?
Many thanks Christine

[EVguru]

I've never bothered with O-rings on the idle stop screws and not usually had problems running without O-rings on the mixture screws.

The air admittance valve was another possible cause of the revs hanging. I'd get rid of it alltogether to allow the crankcase to breathe properly.

The advance curve is very abrupt and once the engine is warmed up there's sometimes not enough friction to pull the revs back down below the point at which the advance kicks in and you end up with the revs 'hanging'. Backing the timing off a little at a time cured this problem on my Dart. Don't get fixated by what the ignition timing should be. Fuel has changed a lot since the handbook was written.