TOPIC:

Carburettor help please!!!!
I cannot get my 350 idling correctly. Carb has been cleaned in ultrasonic cleaner. New idle and main jets. Other cleaners cleaned and blown through. New needle. new o rings and gaskets. Bike starts and runs well at higher revs. However it just wont idle well and progression off idle is terrible. The idle is smoothest and highest speed when the adjusting screw is seated. How can this be??? The PHF idle mixture is regulated by a screw downstream of the slide that regulates the QUANTITY of mixture coming from the idle jet into the venturi. Surely when the idle mixture screw is seated there should be zero mixture and the bike should stall???

How is the bike idling (albeit roughly) when the idle mixture screw is seated????

All jets and needle are as per factory spec. Floats set at 18mm as per Dellorto tuning guide

running out of ideas...

Have you closely examined the atomiser jet? I had a problem with my Giubileo 98 that was running super rich at idle which turned out to be the atomiser so ,worn that too muchmixture leaked past the needle when the thottle was fully closed and idle mixture screw right in..That was a bit easier to diagnose as it was also puffing out black smoke when revved gently. How does it react to turning off the fuel while running? My 98 would start to rev really high as the float chamber emptied and the mixture leaned off.The plug was also really sooty after idling for a while.

Alternatively, many Morini folk find that Dellortos need a smaller idle jet than standard with modern fuel.Worth trying a size down on specification.

Check the small rubber disc on the choke plunger, if need be, remove it using a pin and turn it round 180. Check the cable adjustment on the choke, needs to have enough play to let the plunger and the rubber to seat properly, otherwise, rich mixture, and won't idle properly.
What colour is your plug?.
Alan.

I examined the atomiser jet with my eye glass didn't seem worn and bike only has 20,000km but for the small amount of money I'll get a new one. When I turn off the fuel the idle speed increases to 2000rpm until fuel is exhausted and engine dies.

Hi Alan.

The choke plunger is brand new and there is 1.5mm free play in choke cable.

The atomiser wear would be pretty obvious if enough to cause a problem. It might be worth trying a size smaller idle jet though.If it's speeding up to 2000 with the fuel off that does sound as if it's running rich with it on. Float valve needle tip perfect? Though you would expect obvious flooding if not.

The combination of throttle stop position/idle mixture screw can be tricky. Sometimes worth backing them both right off and trying again with 1 1/2 turns out on mixture and a low stop position so that you have to hold it on the throttle slightly to get it started. Then bring up the idle speed to steady before tweaking the mixture. I guess you've already tried that though.