Help with carb, I think

[bert49uk]

I have recently returned to scooter ownership and have a Lambretta with 185 upgrade, I was told when I bought scooter that its only done about 100 miles since rebuild.
Its had the 175 crank put into a 150 with Suzuki 185 piston, running a new looking Jetex carb, I was told it is slightly over rich jetted to help with running in.
Scoot starts and runs fine, if you accelerate after overrun, there is a reluctance at first to pick up, bit fluffy, but it does clear
On two occasions it has cut out when I’ve stopped, it will start fine but not rev or pick up opening the throttle makes no difference, it won’t clear itself
checked plug, it was wet, cleaned it. no difference, only way I can fix it and did this both times, remove air cleaner and bellows from carb, it will then start and run fine, put it all back together everything runs fine, Both times I’ve noticed fuel in the bellows, there are no restrictions in bellows or filter that would stop it breathing, so I’m at bit of a loss, may be running too rich? sticky float? what do you think,
I would appreciate your thoughts on this problem,

[HxPaul]

Sounds like its running much too rich.What colour is the spark plug?

[bert49uk]

Plug looks black so too rich, but she does run well, and as I've said guy that fitted the engine says she should be a little rich, any idea what would be correct plus for this engine.
She ran fine yesterday for about 20 miles but then same symptoms when i cam to stop at some lights

[HxPaul]

I run a Casa 185 with a clubman exhaust,I have a 45 pilot jet,it 4 strokes on anything richer and a 128 main jet.If your jetex uses the original jets,its best to change them for Dellorto ones.The spark plug is an NGK B8ES.

[Burnside]

What is your carb set up currently? Worth checking that the float isn't sticking, which the Jetex carbs are notorious for, this could explain the difficulty starting when warm as it's probably flooding. On one of my scooters, I have to turn the fuel off before stopping and then when I start her up again when still warm do so without turning fuel or choke on...and leave the throttle alone when kicking over, don't blip it until it has fired up

[bert49uk]

Thanks to everyone, couple of things,
it never fails to start, hot or cold, just won't rev, and is rich when problem happens, I'm coming around to thinking its flooding, so will check float
once clear its fine runs like a train
scoot came with an old Lodge plug, will change to B8ES

[Monty]

The Jetex carb gets a lot of flack but at the end of the day thousands out and running without problem. You say you are getting fuel in the carb rubber and that it runs ok or better without the rubber on. Generally I would say you are running Rich but the first think I would do is remove the rubber and see if you are getting a lot of spit back. jetex carbs collect the fuel inthe rubber so melt a couple of holes in the bottom of the rubber to get rid of any build up. A hot pin on the gas cooker will do not on the bike....The original carb rubbers had a pipe on the bottom. The floats do stick so worth checking you have a red tip float needle fitted the black ones are no good with ethanol laced petrol and stick. 2nd get a bit of sand paper and rub the side of the plastic float reducing the size of the pivot of the float so it can move sideways on the pin if that makes sense. After that it's pilot and main jet. If it starts well and ticks over go down a couple at a time on the main jet. Keep checking plug colour as you go don't go mad. My other bug bear is don't go sawing at the throttle when starting leave the ruddy thing alone till it's running. Good simple carbs with a few s**t ones flying around IMO

[bert49uk]

Thanks Monty, that gives me plenty to do tomorrow

[Scooterdude]

I've recently had exactly the same problem and although I'm using a different carb to you (PHBH28) I eventually found the mixture screw was adjusted incorrectly, once I reset this all has been fine but as others have said don't touch the throttle when starting from hot.

[bert49uk]

Ok people, in last couple of days I've removed carb,
it would appear it has a 130 main jet and 50 pilot
I have sanded the float as suggested, it was slightly tight, and run a 2.2 drill through the float jet.
with the filter bellows removed I'm getting some spit back, but not sure how much is "normal" if I rev the atomised fuel spits back almost looking like steam, I've also noticed a few drips comping from the two brass inserts in the outer face of the carb.
not had time to go for a run, but it still hesitates to pick up when the throttle is opened.

I have not yet made a couple of holes in the bottom of bellows as I'm a bit reluctant at the moment due to the scooter being kept in our kitchen! don't want to stink the place out with petrol, but if I have to I will