Modern Vespa

Hi, I have this engine in my '58Allstate, but it keeps fouling plugs. What is the correct plug or best plug to use in this?

Sounds like your plug is a symptom, not really the problem.

How does the fouled plug look? Does the engine smoke excessively?

I would fit a b6es in a stock motor. Fouling plugs is not usually a plug issue, more carburettor adjustment or ignition issues. If you're unlucky it might be a mechanical problem.
Which plug are you running? Post a picture, we might be able to tell what's up.

Has it had this problem from the start, never run right? How do you usually ride it, more lots of gas & revs & fast, or more just putting around lower speed, low RPMs?

Are you turning your fuel off when parked up?

I don't know what happened. Sitting for weeks, fired up after 3-4 kicks. I let it idle for a while before riding, so it was probably loaded up with fuel. then stalled and couldn't restart. not sure if this plug is correct or not. Not sure if HS and ES are vastly different. Can anyone tell me the correct one for an LML engine?
Mercato I believe says ES.

PS I closed gap to .008 as well.

Please school me thanks!

Thats way too rich. You could try a hotter plug, a 6HS. You could try adjusting your mix screw on your carb. Possibly a leaking seal, would guess crank but im sure an expert will come on board soon. Rule out the obvious first, clean your carb out, carb spray all the jets etc, clean your air filter (lack of air = rich). Check you havent put a mix jug under your seat in the air intake hole of frame, or a rag blocking that. Adjust the mix screw at back, couple of turns out to start and go from there.

Thanks. What's the difference between HS and ES?
Could have been too rich from idling and me trying to kick it over 100 times. Was really wet and fouled up.

Short reach HS and long reach ES. You put a long reach in something needing a short reach you will blow a hole in your piston. The number is the heat rating. So a 6 plug runs hotter than a 7. Ive got a kitted PX to 177 so I generally run a 7 around town for thrashing about, however, on a longer run i run a cooler plug, the 8; the 8 isnt great on my scoot for local trips so i swap out according to my journey plans. The higher the plug number, the cooler the plug remains (colder plug). Hope this makes sense.

So I need to continue with HS? Not extended threads ?
I'm confused because I thought I had an LML engine and on Mercato it says to use an ES plug
But I had an HS in there…

Well wait for an LML owner to come on here and tell you what you need. Ive never owned an LML, i know the later ones had different port layouts etc to a PX and perhaps different crank stroke. Your picture shows a short reach plug.

I've never owned a Stella either but pretty sure the LML 150 is an ES plug. The Vespa PX150 is an HS plug

Stella plug is ES, but that's for reed intake. OP shows rotary intake. I think LML made both. Plug might be different.

If you've had the scoot unabated for long enough, no changes are necessary, just ride the piss out of it. Idling too long does cause this.

I didn't know that but I'm not surprised. Maybe could be your problem?

Both my reed valve LML motors are long reach, but it really depends on your head. Easy to check w/ a good flash light looking down spark plug hole, or if you're unsure, it's not hard to pull the head and verify.

Or put a screw driver down plug hole and measure when piston top position. If it's supposed to use short reach and you put on long reach you will punch a hole in piston crown . But yes as suggested take off cylinder head and check by putting plug in, seems sensible .

That's a good idea that will help you decide, and agreed, pull the head to 100% confirm. But let me go look down that hole w/ light... BRB

Interesting, you can see to tell but you almost need to see both types to know the difference. I also wanted to see if a long plug in a short plug motor would actually hit the piston and punch a hole, or would easily burn a hole when the adjacent area gets too hot and turns to aluminum cheese before blowing thru.

Regarding a long plug in a short plug engine, I suspect it could have an adverse affect on the propagation of combustion.

I thing the bigger problem would be carbon fouling in the plug threads, making plug replacement a real SOB of a job.

One quick way to tell how deep the thread goes is with a long matchstick or similar. Gently rub it round the plug hole thread and it will leave a tell tale dirty mark.

I was once going to buy a PX150, i took it for a few spins to see if it were for me, i was on way back to seller when scooter died. Pushed it back, pulled the plug, it was a long thread plug, wrong for that model, guy takes off cylinder head and a dirty great hole in the piston crown exactly in same position as the spark plug. Safe to say didnt buy, and a lot of work for seller to strip engine to remove fragments of piston.

Yep, gets too hot where the fire starts too close to piston = aluminum cheese starting somewhere over 400 when mechanical strength falls off a cliff, but only melts and turns liquid at over 1200°F. You blew a hole right thru it long before it might melt, but that damn cheese will smear and stick even if it won't flow

update- got the bike running yesterday, new plug 7HS. would start on a spray of starting fluid then goosed it to stay running but then would die. By holding the choke on it would start again and run but wouldn't idle. This was not the case prior. it would run and idle fine. Should I mess with the idle screw? I forget which way to turn to advance and retard...
Thanks!

Check the gear oil to rule out a seal leak

Turning it in (clockwise) leans it, counter clockwise richens it.

Have you cleaned out the carb ? Complete strip down , carb cleaner , compressed air, air filter , filter to float bowl, gaskets, float etc . Take it off and give it a good going over. Then whilst carb out adjust mix screw to 1.5 turns out for starters . As jack said , drain off gearbox oil into a plastic pot, if it stinks of petrol you've got a leak, maybe crank seal flywheel side.

I think you are both referring to the mixture screw, the idle screw affects neither advance nor retard, nor how lean or rich it is.

Maybe this would help you dial it in: Mixture screw adjustment, got a good link?