Stuttering & four stroking

[Lambretta67]

Hi my standard G.P. 200 has started stuttering & four stroking at low revs when changing gear. I'm using a standard 22mm carb. I have to drop down a gear & give loads of revs then change up. Ticks over fine & runs fine when opened up. Any ideas please

[Daggs]

You say "started stuttering and four-stroking" Does this mean it previously ran well and this is a new thing?

[Lambretta67]

When I first got the scoot 5yrs ago it started doing the same thing. I changed the dellorto atomizer for a jetex one of the same size & it seemed to cure it. Have done about 6000 miles on it with no problem but now it's back with a vengeance. It's a original 22mm dellorto carb I'm using so its it's probably a bit worn.

[EddieStone]

Could be a leaky needle/float valve. Atomisers don't wear in these carbs, to be honest.

[Lambretta67]

I haven't checked the float needle yet. I changed it about 5years ago. It might just be coincidence that scoot ran fine when I changed the atomizer for a jetex one last time it played up. Seems strange its doing the same thing 6000 miles later..plug is a very dark brown.

[EddieStone]

Do a bit of research or call a decent shop to make sure you get the right one. There are two lengths possible, I think, and different tip materials.

[Lambretta67]

Black one was in the carb when I bought it. I fitted a red tip one I bought from scooter restorations.

[Daggs]

If it has happened during the recent hot weather, this could be the answer.
I don't agree with the idea a leaky float valve would cause this.

[coaster]

It could easily be due to the warm weather as it will run rich when the air temp goes up.

[Lambretta67]

You might be right. it started yesterday when I was riding back from work. The temperature was in the 30s. Was fine when I road to work in the morning at 5am when the air was cooler