Modern Vespa

Same ole problem.
Details
Stella 2005 2t
Kitted with Malossi 166 cc
24/24 Si Carb 130 main, 55-160 Idle, 160 Air Corrector Jet
Huge Piston Ported expansion chamber Boomstick.

I've been fighting this set up since last year. Finally got the main jet just right. Not to rich, not to lean. I've looked and looked for a air leak. Can't find one.

It's extremely slow at take off in 1st gear until it gets into a power rpm range, it kicks in and it revs nicely through the 2,3. I get to 4th and it bogs down at any hill or dale or wind for that matter. So much so, I have to down shift to 3 and wind it up to almost 45 and shift up.

My carburetor back blows fuel and it drips more than usual.
The back mixture setting is 3 rotations out.

If it posted the sound of it winding out would that help with the diagnosis?

Very frustrating.

What Atomiser, BE3?

55/160 is probably too big. And 3 turns out on the mixture screw is too far.

What is the timing set to?

Any of these could cause your issues but excessive blow back with no mechanical issue, is a sign its all way too rich.

BE3 Atomizer.

So the plug does not look too rich. It's a nice light tan.
I am considering going back to my 20/20 SI carb and starting the main jet mambo all over. My milage sucks.

One thing of note, when I tighten the idle mixture screw all the way in it does not stall. I thought that meant an air leak, but again, i can't find it.

Timing is set to 18 degrees, I had to modify the LML stator holes to get there.

if you screw the mix screw all the way in and it doesn't stall, your idle screw is in too far and you are feeding from the main. take a pic down the carb barrel of how far open it is when you are at 0 throttle.

I thought if you screw it in all the way and it doesn;t have an effect then the idle jet is too rich.

Closing it all the way should stop fuel flow through the circuit until the throttle is open enough to transition to the other part of the idle circuit.

As Ginch and John have both said and I agree the pilot is not set up correctly. The mixture screw responds more to the small number on the pilot jet. Yours is 55, I would expect your set up to have about 45 maybe 48 as the first number. When the smaller number is too big the mixture screw seems to not do anything. It is easier to start weak on a pilot jet and work up but care must be taken to not go thrashing around with a weak jet.

Timing at 18 is ok. As long as it is 18 and checked with your own marks made by a degree wheel and using a strobe lamp.

The 24/24 carb will dial in. Its the same job to dial in either carb and the 24/24 will go better, if its all been blended in smooth.

The poor gas mileage confirms its too rich. And this is more than the pilot jet. Was you plug colour check from WOT run? Carbs deliver fuel on a curve and it can easy be lean one end and rich the other. Or the just the middle. Its all possible.

I have almost an identical set up: 05 vespa px150 , Malos 166cc , broomstick, 24/24 carb with a 115 or 120 main jet(the kit came with a 115).

I can get to speed just fine but it lacks balls. Accelerating from a dead stop is very sluggish, I mean, really sluggish until I get to the higher revs.

I recently had the sito plus which was a little better on low end and mid range. I can hit 72-75 up right on the speedometer without issues but GPS tells me 65mph max.

you have to get use to the underperforming qualities of the malos 166cc. In my opinion it is a very weak kit. I picked 12mph compared to stock but it is because of the revs. The kit is "ok", I wouldn't buy another malos 166cc again ever. I had a poling 177cc (old cast iron) on a Stella and it was very torque and fast, much stronger than the malossi.

try a smaller main jet, I have a few other scooters (all of them kitted) and when I put a jet slightly larger that is when I lose top end and power in general(it bogs down).

Did you checked your spark plug?

I check the spark plug often. I will reduce the pilot jet and main and give it at go. It's funny, I reinstalled the old 20/20 SI carb, just to see if the 24/24 was pumping in to much gas. What a waste of time.

I'm back to the 24/24. I hit 55 mph on my way in. Better.

Tanks for the advice...

So last night, I put in a smaller pilot jet, BE3 Atomizer and a 115 main.
Fired right up and ran like a champ.

Still sluggish in 1st gear until power revs. Much better in 4th gear.
I'll check plug after commute tonight, hopefully it's not too lean.

Thanks for the advice

Going in the right direction by the sounds of it.

Which pilot jet?

That's quite a jump from a 130 to a 115. I would have gone down 5 at a time.

50/120 Idle jet.

I thought long and hard about stepping down from the 130 Main.
But the 115 came with the Malossi kit. My plan was to step up if it was at all better. It was so much better. I'm not sure how I got to the 130, but I was going in the wrong direction

I'll wind it out tonight and do a plug chop. Devil's in the details.

It might feel a bit better off tickover but 50/120 is not ok. This is nearly one of the biggest jets!

Your choices are 45/140 or 48/160. If you haven't got either, then order the 45/140.

Be sure not to ride too hard until the plug has been checked from a WOT run.

I have both of those, I'll swap out at garage night, tomorrow night.
Thanks Jack