Modern Vespa

How many turns out is the mixture screw?

But you're running a 177 kit…

A 210 kit uses around a 130-135 main (in general, with a few varying factors…)

An you're not even running a big pipe.

I'm reading you saying "lurching" is different to "surging"?

Lurching as in its like the scooter does an on/off throttle action, when you actually don't do anything?

I bought the bike with the same kitted fitted but it seized on me. It had been built by reedspeed and put on the dyno with the jetting as: 140/BE5/105 with 52/140 idle. It has a upgraded chamber cover and hole in carb for main jet drilled to 2.5mm. It seized on me at WOT after a good 5 or 10 mins. Massive soft seize on the intake side of piston. It was well and truly melted. I have upgraded the main jet to 112 and the plug colour is a medium brown. It feels rich when pulling away as it splutters a bit put then picks up nice. I cant see how reedpseed would set it up incorrect and a main of 130 seems huge. I have fitted a sip 2 tap. Running autolube with 1% extra in tank. Squish is quite high at 1.4mm. Cant get it any lower unless I remove the base gasket. Port height is good for all ports. Timing on stator is retarded as far as it will go to the IT setting. Compression is 170 PSI cold and 155 PSI after a run and warmed up. Its a 2016 PX150E.

I had a be5 ac140 and 122 mj on a DR177 which is not much more than a big bore upgrade and road 2; that was spot on so no wonder yours seized . I'd go back and demand they repair else you will cause a stink.

I had a be5 ac140 and 122 mj on a DR177 which is not much more than a big bore upgrade and road 2; that was spot on so no wonder yours seized.

It's definitely 4 stroking due to being a bit too rich, but this is only at low revs and doesn't bother me. If I keep the throttle open when 4 stroking, the engine temp starts to fall. I will just ride it as it is. I very rarely ride it wot so not that arsed. Temps are good which makes me not worry too much.

Did you put the pinasco Venturi on yet? What is the pilot jet now? 65/160?
Reduce the main jet until the 4 stroking goes away. Then tell us what happens.

In my ltd knowledge of the dark art of jetting if your temperature starts to fall that surely implies you're too lean on low throttle? Lean equals hot hence heat seizures . I gleam my Understanding from the gurus on here and still messaging members for advice. Your pulling away sputtering sounds more like having too lean pilot, you think it's too much fuel but it ain't, it's lack of fuel hence the lurching about. Get some richer pilots experiment .

I am done with the venturi as it seems to fuck it all up and doesn't quite fit under the box lid. I won't be fitting that. I am running 120/BE4/138 and 62/160 @ 2.5 turns. It only 4 strokes when riding at certain partial throttle, literally just off idle. It does not splutter at all when pinning it in any gear.

Here is a picture of my vortex. Fits fine. Whats different on yours?

If the engine is not leaking the 138MJ is way too big. Should be nearer 118. Could be hiding that your pilot jet is too small. There is so much bleed over its really hard to tell.
Put in the 68/160 pilot jet. 2.5 turns. Start reducing the main jet until it feels good and the mid spluttering has gone.

118 main a bit small? Not really…

You might end up around 125.

I just put a 132 main into another Malossi 210 with 60mm crank, si26 carb with a JL pipe…

It's a common jetting size on a 221cc, and it's been like that for years.

So it doesn't make much sense you're on bigger jetting with smaller cc

I just don't want to blow it up. I don't understand how the Dyno afr graph was spot on with the current 138 main jet. 20 jet sizes down seems excessive especially when the bike revs clean all the way. Temps around 155 wot in 4th when the temp settles.

Er, no mate…

Plenty of stories of where dyno runs got it wrong…

Perfect dynos, runs like shit on the street. Even seizes because it was jetted perfect on the bench, then blows up because the test is literally 60secs where on the street you have riding before and after when you try WOT.

If the dyno afr graph is right, there's a problem with your engine.

I'd definitely trust my own years of riding around with the si carb.

Nailing the pwk carb jetting with the info from jack, cm 1 and 2 and the rest of the guys, just proves the methods work.

Vortex has VRX-R on it. Same one as this one. They fit.

Don't go straight down to 118MJ. Just Drop a jet at a time until it feels better. With AC120/BE4/138 its sure to be way too rich. Whats the plug look like after a run?

The 138 main revs out correct in second gear and splutters. How can this be wrong?

Yeah sounds like your engine isn't quite right…

But go back to your previous settings if they work for you…

Plug looks rich but not overly. Not being black is what matters at the moment. It is running cold.

The lurching on rundown is usually a lean set up or air leak. Next time out do a recording of what it does with the 132 in.

So hard to guess with the main jet. It is an RX190 but running on a box pipe. Dyno tested at 15bhp with acceptable rich AFR. What does the plug temperature get up to at WOT? Jets can be way of size +/-10 is not uncommon.

I don't think that my pilot is lean at all. If anything it's rich. How would being lean reduce the temp and being rich increase the temp? You have lost me there.

You said this 'If I keep the throttle open when 4 stroking, the engine temp starts to fall.' I was implying that a lean pilot would increase temperature and when you open throttle it cools because you are introducing sufficient fuel being the coolant. I didn't say lean pilot reduces temperature , when you open throttle your temperature drops, it's the fuel that cools the engine. I tried a leaner pilot in my177 as thought I was rich bogging and it lurched about, when I did plug chop the core was very pale. I changed the pilot to a richer one and the engine ran better and plug returned to brown, I wasn't rich bogging at all, I was running lean on pilot . Ended up with a 120 / 50 , a 2.4 mixture and then had to also slightly richen on the mix screw to iron out the slight splitter on minimal throttle. Jetting is tricky , it still confuses me hence getting advice on here but I've learned a lot, still a way to go.

Now I get you. Cheers.

Just fitted the 55/160 and 138 main. Runs so much better with the smaller pilot. Revs don't hang. Exhaust starts popping at around 3500 rpm but I think that's just the exhaust on the rundown. Could a too rich idle cause the lurching issues? Then again when riding wot with choke out, there is no lurching when closing the throttle. Weird.

The other thing I've been told many times is that there will always be some compromise with kitting in running. Ability to drive like hooligan WOT but some splutters at low throttle etc. some days i just wish I had my standard p200 back where it chugged along about 55 cruising and topped out 62 mph , smooth as silk, standard pipe and no pissing about with jets.