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The 252 hadn't been long built when I re-assessed my timing. With a static Vape CDI Itried to adjust it so that it would be about 18 or 19 at a nominal 6000rpm. There was some guesswork involved, as it turns out my guess didn't work. But man it went well for those few minutes! ROFL emoticon ROFL emoticon

Fast forward past the pissed-and-broke joke, I was just thankful the bore was ok. Perhaps I should say mostly ok. Turned out the top edge of the exhaust port had lost a little nicasil. So I thought I may as well grind it out, otherwise it's a new cylinder! And the piston was already a couple of hundred dollars so I was not keen on padding Mr Q's account any further just now.

It went well. I left it at more of an arch than a flat line, when I measured the port timing - an anxious moment - it had arrived at 188/126. Previously was 176/126. The numbers certainly didn't seem ridiculous so that was something of a relief. Scooter Center did a blog in 5 parts building a 252 (they used a Kingwelle crank which has a 128mm rod instead of my 127mm Uncle Tom), and they tried lifting the exhaust to 190 and found power down a couple of horsepower around 5000 using the Polini Box like mine.
So I was slightly anxious I hadn't killed it after all.

Needn't have worried. It was fantastic! With no other changes (except correctly timing it!) you could really feel the extra power right throughout the rev range. But mostly over around about 6-7K rpm, where it just kept accelerating. When I passed a restored Datsun 120Y (makes you feel old!) it actually gave me a bit of a fright as I glanced and saw I was doing 118 and it was still pulling hard!
And the amazing thing, the temperatures seemed lower and more stable than previously. After a 40 minute run mostly around a very relaxed 100km/h, the temps sat between high 330's and 350, which I'm pretty comfortable with.

A very satisfying experience.


Did make me think about the dyno posted by FMP a little while ago, sorry a bit blurry. I was pretty impressed with the Malossi Box vs the Polini, with a fair bit more to give at the higher revs. A mate had a PM pipe on his 221 and the swap to the Malossi Box gave more power all round , including a higher top speed.
Might be one in my future.

https://en.blog.scooter-center.com/alex-builds-a-quattrini-252cc-vespa-engine-5/
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Great story. Everything you've done is ballpark ok.
Wasn't timing that broke the piston. Keep all that the same.
I suspect what caused it, is from running lean with a squish clearance/angle that's inappropriate.
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Ah that sucks…

Glad the rider is ok…

Yeah the top of the piston looks super lean… even if it's been cleaned a bit, don't think it should be matt black on the edges…

Timing might have given the false impression you were running ok jetting.

Edges should be golden brown washed colour.
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Interesting comments to ponder, thanks!

When that happened I was doing my usual test run, 9km pretty straight road with no stops. Half 80km/h zone, half 100km/h zone. Temps previously had been what I would describe as under control. On the last run of said piston, it climbed very high and stayed there. Should have backed off much earlier but lessons wouldn't have been learned so convincingly! I stopped to do a U turn and it cut out, wouldn't start again.

On previous timing I had done that exact run with lower temps and the piston stayed intact. I'm sure the jetting is far from perfect (hasn't changed before or after), however the only variable here was the timing. I realise that 108 has been talking a bit about timing changing jetting, not sure how that actually plays out and the steps you might take.

Squish is unchanged from before, very close to the recommended (maybe slightly bigger?) if I recall correctly? Quattrini stock 244 head so whatever squish angle that is... no changes from before. The piston came out exactly as it is in the picture, no cleaning.
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Ginch wrote:
Interesting comments to ponder, thanks!

When that happened I was doing my usual test run, 9km pretty straight road with no stops. Half 80km/h zone, half 100km/h zone. Temps previously had been what I would describe as under control. On the last run of said piston, it climbed very high and stayed there. Should have backed off much earlier but lessons wouldn't have been learned so convincingly! I stopped to do a U turn and it cut out, wouldn't start again.

On previous timing I had done that exact run with lower temps and the piston stayed intact. I'm sure the jetting is far from perfect (hasn't changed before or after), however the only variable here was the timing. I realise that 108 has been talking a bit about timing changing jetting, not sure how that actually plays out and the steps you might take.

Squish is unchanged from before, very close to the recommended (maybe slightly bigger?) if I recall correctly? Quattrini stock 244 head so whatever squish angle that is... no changes from before. The piston came out exactly as it is in the picture, no cleaning.
Was there head centering spacers? No extra gaskets?
19 degrees timing is nothing special. Piston looks really lean. If the head checks out, this is all down to jetting. Not perfect jetting can run fine for many years. For detonation on this level it's way off. This needs a full rework, soon if still running the same jets.
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Jack221 wrote:
Was there head centering spacers? No extra gaskets?
There is an extra gasket in there, no head centering though.
Jack221 wrote:
19 degrees timing is nothing special.
What do you mean by that? Good? Bad? Ok?
Jack221 wrote:
Piston looks really lean. If the head checks out, this is all down to jetting. Not perfect jetting can run fine for many years. For detonation on this level it's way off. This needs a full rework, soon if still running the same jets.
I'll need to check again what's in there currently, I made quite a few changes a few months ago but nothing since.

Appreciate the advice.
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Finally found the photo of the top of the piston just under 100kms of running. See below.

I found that the more advance timing is set, the richer the bottom end jetting should be.

Can't remember if you're running a vape sport or road… assuming it's a sport

If you're hitting 18-19 @6000rpm I'm assuming it's around 23-25 @ 1700rpm.

Your jetting will be richer than if you were running a road 15-16 @1700rpm.

So that's pilot, needle, atomiser and clip setting. Main generally stays the same.

If I remember correctly it's a phbh 30.

Vespas will work with a 55 pilot, I would use that, you could try 56-58 but I doubt that's the cause of your explosion.

The AS264 would be the red flag in my mind… it's a bit lean from 1/8-3/4. Which would probably explain the grey piston top…

The x13 vs x2 needle is the same diameter just with the x2 the taper kicks in earlier making 1/2-3/4 throttle richer. Which would be a performance tweak rather than cause an explosion
Q244 Pwk 30 carb. Still a tad lean. But more than ridable.
Q244 Pwk 30 carb. Still a tad lean. But more than ridable.
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108 wrote:
Finally found the photo of the top of the piston just under 100kms of running. See below....
I'll get the current jetting tonight after work. I have a Road "static" CDI which is set to 19 degrees at idle speed. So not sure how that translates to jetting at the moment... your comment "I found that the more advance timing is set, the richer the bottom end jetting should be" is very useful though.

I'll see if I can use the scope thingy to get a photo of the piston that's in there now.
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Ginch wrote:
There is an extra gasket in there, no head centering though.


What do you mean by that? Good? Bad? Ok?




I'll need to check again what's in there currently, I made quite a few changes a few months ago but nothing since.

Appreciate the advice.
19 degrees on a static vape will reduce below 18 at max. Ignition timings version of vanilla. Suits every occasion. This didn't cause the problem.

Need to add some head centering bushes. This might have been a factor. Without bushes the head can bolt down not central. This makes the squish tighter on one side.

Jetting is the main issue. What's all in your carb?
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Ginch wrote:
I'll get the current jetting tonight after work. I have a Road "static" CDI which is set to 19 degrees at idle speed. So not sure how that translates to jetting at the moment... your comment "I found that the more advance timing is set, the richer the bottom end jetting should be" is very useful though.

I'll see if I can use the scope thingy to get a photo of the piston that's in there now.
Yeah, would be good to know what you ended up at with jetting.

19deg at idle would make you run hot, you'll be at 21-22deg at around 6000rpm. Usually not a problem, but yours is not a stock engine… lol

It should be around 15-16deg at idle (or around 1700rpm) probably a fatter needle but bigger atomiser… lean down the bottom end…

That's probably why it felt really good before… rides great in short stints but not so great sustained (as the piston says…)

Oh forgot to ask, 4% oil?
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Jack221 wrote:
19 degrees on a static vape will reduce below 18 at max. Ignition timings version of vanilla. Suits every occasion. This didn't cause the problem.

Nah… it doesn't, unless you go 13000rpm… lol
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108 wrote:
Nah… it doesn't, unless you go 13000rpm… lol
Need evidence or you're just making it up
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Jack221 wrote:
Need evidence or you're just making it up
Nah, not making it up. See below…
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108 wrote:
Nah, not making it up. See below…
Ok, this is better, just under one degree not just over one degree. I'll bet you're an accountant.
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Yep 4%.

The current jetting is:

X25 needle (2nd clip from top)
AS 262
Main 140
Idle 52

And here's some pics I took just now.
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Jack221 wrote:
Ok, this is better, just under one degree not just over one degree. I'll bet you're an accountant.
Well… I wish…

But if you start at 19deg idle (1300rpm) that's -2 and you'll only ever reach 0 at 7000rpm (thats 21deg…), you'll never go lower than -2 (never below 19deg…) that's why sustained 7000rpm, at 21deg, with the squish and compression of the 252, things will melt without the right jetting.

Designer by trade… if I was an accountant, I don't think I'd be here spending the amounts of cash we have on vintage Italian scooters… lol
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Ginch wrote:
Yep 4%.

The current jetting is:

X25 needle (2nd clip from top)
AS 262
Main 140
Idle 52

And here's some pics I took just now.
Hey that's not too bad looking… yeah I don't think I'd do a AS262 though.

Temp readings are a bit of a Bermuda Triangle I think. I don't have much experience with using them, because it seems even with people using them, it's too delayed to be warning you (unless you're really in the lucky few…)
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108 wrote:
Designer by trade… if I was an accountant, I don't think I'd be here spending the amounts of cash we have on vintage Italian scooters… lol
If you were an accountant, you'd have a Harley and hang out with the Sons of Accountancy at the local coffee shop on a Sunday morning. Razz emoticon

I'm a building designer.
108 wrote:
But if you start at 19deg idle (1300rpm) that's -2 and you'll only ever reach 0 at 7000rpm (thats 21deg…), you'll never go lower than -2 (never below 19deg…) that's why sustained 7000rpm, at 21deg, with the squish and compression of the 252, things will melt without the right jetting.
So if I set it to 15-16 at idle where does that put me at 7000?
108 wrote:
Hey that's not too bad looking… yeah I don't think I'd do a AS262 though.
I'll try going up on the atomiser, previously this was the only one that would run cleanly.
Jack221 wrote:
Need to add some head centering bushes. This might have been a factor. Without bushes the head can bolt down not central. This makes the squish tighter on one side.
I did think about that when putting it together, but couldn't think of anything straightforward at the time. Any suggestions for that? Years ago I had a Pinasco 177 (I can talk about it now without getting that nervous tic...) and I bought centering bushes for it, little sleeves that sat in the stud holes. I think the Q244 has very little to no additional space in the stud holes from memory.
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Ginch wrote:
I'm a building designer.

So what you're saying is that if I was an accountant, I'd suck… lol…

Graphics designer here, lowest rung on the ladder…
Ginch wrote:
So if I set it to 15-16 at idle where does that put me at 7000?


I'll try going up on the atomiser, previously this was the only one that would run cleanly.

With 15-16, you would end up at 17-18deg @7000rpm

I'd try AS 266… and then play around with the needle clip position. I'd still hedge my bets on x2 or x13 needle…
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108 wrote:
Well… I wish…

But if you start at 19deg idle (1300rpm) that's -2 and you'll only ever reach 0 at 7000rpm (thats 21deg…), you'll never go lower than -2 (never below 19deg…) that's why sustained 7000rpm, at 21deg, with the squish and compression of the 252, things will melt without the right jetting.

Designer by trade… if I was an accountant, I don't think I'd be here spending the amounts of cash we have on vintage Italian scooters… lol
I was basing my whole train of thought on this, that Ginch said at the top of this thread.
Ginch wrote:
With a static Vape CDI Itried to adjust it so that it would be about 18 or 19 at a nominal 6000rpm.
18/19 degrees at 6000rpm is normal for this kind of cc. Right down the middle of big yawn.
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Check ignition timing at at least 4000 RPM's to know what it's going to be at actual rubbing speeds. This is also a great time to get a variable timing light, so you just need an accurate TDC mark and no accuracy drift as you mark advance from there.
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Jack221 wrote:
18/19 degrees at 6000rpm is normal for this kind of cc. Right down the middle of big yawn.
Some days I could stand a little less excitement of the metal melting kind.
chandlerman wrote:
Check ignition timing at at least 4000 RPM's to know what it's going to be at actual rubbing speeds. This is also a great time to get a variable timing light, so you just need an accurate TDC mark and no accuracy drift as you mark advance from there.
I know. You say it all the time, and usually I then go have a look how much they are and think 'next time'.
For some reason I always find the timing light on the Vespa... less than conclusive. Just had a look a FMP timing video and the marks were rock solid and predictable. Not really my experience to be honest.

When you adjust your light for the advance you want, what happens then? How do you then know how much to move the stator?

And your suggestion is 18/19 at 4000?

108 is on record as 15/16 at 1300

Jack is not on record yet but thinks 19 is time for a snooze. Laughing emoticon
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I'm on similar page to CM.
And picture below says it all.
I just don't understand how anyone sets timing at idle.
What idle?!
F*king things idle at 3 different RPM all at once - and that's the charm of a 2 stroke at a stop light!

Add in the parallax effect of the distance from flywheel to cases and it makes it all relative.

Ginch - are you setting timing up at about 4K?
In my view - you have to rev motor until you see the change in direction of the advance.
That is the point you want to set at.
Get it to hover there.
Do the math - to work back to your other settings.

You may have more than one issue - and you solved at least half taking some timing out.
Piston suggests.
Temps suggest.

Agreed - temp read is often more a confirmation of goodness than an in the moment tattle tell.

Anyway - Static or variable - best set right at the balance point.
Get a helper to hold the throttle for you if you can.
Will be most accurate.
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charlieman22 wrote:
Ginch - are you setting timing up at about 4K?
In a word, no. Just idle. Maybe a fast idle.

In a version of "how many jelly beans in the jar", what number do you suggest it read at 4000?
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Ok.
First pic - I failed to post - shows the issue of trying to set at "idle".
Every 250 rpm change = a full degree of timing change.
Just about impossible to set, thus 4K at balance point is more accurate.

Assuming 18° as per Jacks post above, at 6k, then about 18.5° at 4K.
Timing curve changes to Steve to try and set timing at low rpm. Hopeless.
Timing curve changes to Steve to try and set timing at low rpm. Hopeless.
You will lose about a half a degree of timing between 4000 and 6000 RPM according to this.
You will lose about a half a degree of timing between 4000 and 6000 RPM according to this.
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Ginch wrote:
In a word, no. Just idle. Maybe a fast idle.

In a version of "how many jelly beans in the jar", what number do you suggest it read at 4000?
Unfortunately guess wrong and you get a melted jar…
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charlieman22 wrote:
Ok.
First pic - I failed to post - shows the issue of trying to set at "idle".
Every 250 rpm change = a full degree of timing change.
Just about impossible to set, thus 4K at balance point is more accurate.

Assuming 18° (yawn) as per Jacks post above, at 6k, then about 18.5° at 4K.
That actually makes sense! Thank you.

Why "balance point"? Is that really a thing, or a term you're using to describe something? Never heard it before.
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Yeah that's the same as 15 deg @1300rpm
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108 wrote:
Yeah that's the same as 15 deg @1300rpm
We have convergence!! Yay!
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Wasn't this a static vape CDI yesterday? Is it now changed to a variable CDI? The kind of beans matters as much as the quantity.
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"Balance point"
When u shoot it with a light, and u start to rev from idle, the mark will move left - or right. I can't recall.

Then - about 4K rpm, it will stop moving left and go back right.
The chart shows that's at 4K rpm - so u don't even have to look at a guage.

It's also the most stable place - so it makes it easier to read.
Just rev slowly and wait for it to change direction.
When it does - make sure u are around 18.5 degrees.
Bobs ur uncle.

Interested to know what u read when u test.
Suspect u r close now — meaning u were in fact off when u burned it up.
But it's just a guess.

Let us know.
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Jack221 wrote:
Wasn't this a static vape CDI yesterday? Is it now changed to a variable CDI? The kind of beans matters as much as the quantity.
(I'll go get my Harley…)
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@ginch avatar
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Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and '66 Blue Badge Smallframe
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@ginch avatar
74 Super, 75 Super, PX project, LML off-roader and '66 Blue Badge Smallframe
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Posts: 8610
Location: Victoria, Australia
UTC quote
Jack221 wrote:
Wasn't this a static vape CDI yesterday? Is it now changed to a variable CDI? The kind of beans matters as much as the quantity.
Yep. Still is today!
I started with a static months ago, tried a variable and went back to static. Timed it (badly), broke the piston, you know the rest.
charlieman22 wrote:
Suspect u r close now — meaning u were in fact off when u burned it up.
But it's just a guess.

Let us know.
Yes I was a long way off. Some days should be labeled "do not operate heavy machinery".

Appreciate the diagram and explanation CM.
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Jet Eye Master
PX221 MHR, O tuned PX200, PX125 and some motorbikes
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Jet Eye Master
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UTC quote
Ginch wrote:
Yep. Still is today!
I started with a static months ago, tried a variable and went back to static. Timed it (badly), broke the piston, you know the rest.



Yes I was a long way off. Some days should be labeled "do not operate heavy machinery".

Appreciate the diagram and explanation CM.
Well this explains yesterday's difference of opinion. 108, CM and CM2 all thought it was variable (vape sport) and as said at the top, it is static (vape road), was static when it blew and still is static now.
The static info is still on the same chart. The numbers on the bottom right.

I was talking about vape road, 18/19 at 6000rpm so is still good but for actually checking it you want to strobe 18 at 3000rpm. Static is not totally static as the name would suggest.

Your jetting is not great, a stock 125 would run on that. Think you've been chasing stutter not splutter. What atomisers and needles you have? See if I can work out a combo.
@108 avatar
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Ossessionato
PX 200
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@108 avatar
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UTC quote
Jack221 wrote:
Well this explains yesterday's difference of opinion. 108, CM and CM2 all thought it was variable (vape sport) and as said at the top, it is static (vape road), was static when it blew and still is static now.
The static info is still on the same chart. The numbers on the bottom right.

I was talking about vape road, 18/19 at 6000rpm so is still good but for actually checking it you want to strobe 18 at 3000rpm. Static is not totally static as the name would suggest.

Nah, was always referring to the vape road, which Ginch has been using since swapping over from a sport CDI forum a while back. In which I mentioned, folks should be jetting the curve. It's not actually static…

That's why I have no gripes about using the sport. The road has a curve, just a different shaped one which uses leaner jetting from idle to around 1/2 throttle.

A lot of the new kits are designed to be using variable ignition… it's obvious when you've tried both on the same cylinder kit and jetted it properly.
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Jet Eye Master
PX221 MHR, O tuned PX200, PX125 and some motorbikes
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Jet Eye Master
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UTC quote
Jetted in better it will be fine
⚠️ Last edited by Jack221 on UTC; edited 1 time
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Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and '66 Blue Badge Smallframe
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@ginch avatar
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UTC quote
Hopefully this comparison diagram will clear up any lingering confusion... pretty sure 108's screen grab comes from the left-hand graph.

As to jetting implements, I have:

Needles - X 2, 3, 4, 5, 7, 13, 44 & 61
Mixers - AS 262, 264, 266, 268
Mixers - AV 262, 264, 266, 268
Idle jets - 45, 50, 52, 55, 58, 62
Main jets - 125-150, 155, 160, 170, 175, 180, 185, 190

Appreciate your assistance as always.
Forum member supplied image with no explanatory text
@108 avatar
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Ossessionato
PX 200
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@108 avatar
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UTC quote
Jack221 wrote:
Yesterday you wrote on the variable curve for the vape sport and posted it. It's still there atm.
A happy accident (Quattrini 252) (Post 2673010)
Experience is just making mistakes and owning them. And I make plenty. Who wants to get old
Yeah, thats the vape road curve I posted and CM2 was commenting on… Ginch was helpful by just posted both.

Must have read that damn manual a million times from each time installing it on a dozen bikes (the basic wiring diagram and the graphs… being most of the reading) and I have a stack of them where the hoarder in me appreciates the print quality too much to throw them away.
Forum member supplied image with no explanatory text
UTC

Jet Eye Master
PX221 MHR, O tuned PX200, PX125 and some motorbikes
Joined: UTC
Posts: 4472
Location: London UK
 
Jet Eye Master
PX221 MHR, O tuned PX200, PX125 and some motorbikes
Joined: UTC
Posts: 4472
Location: London UK
UTC quote
Ginch wrote:
Hopefully this comparison diagram will clear up any lingering confusion... pretty sure 108's screen grab comes from the left-hand graph.

As to jetting implements, I have:

Needles - X 2, 3, 4, 5, 7, 13, 44 & 61
Mixers - AS 262, 264, 266, 268
Mixers - AV 262, 264, 266, 268
Idle jets - 45, 50, 52, 55, 58, 62
Main jets - 125-150, 155, 160, 170, 175, 180, 185, 190

Appreciate your assistance as always.
Nice set of needles. Keeping generally as it is, AS262, 52 pilot and remove the main jet. Without the main jet it's easier to see what's going on.
Set the mixture screw at 1 turn out. Lean.
Put in the X5 on clip 3.
Mark the throttle grip accurately in 1/4 increments allowing for the slack.
Start it up and rev it aggressively to warm it up
Open the throttle almost full and find the point where it revs the highest. Note down this rpm and throttle position. Hopefully something near 10,000rpm.
Hold 1/4 throttle steady and it will rev high. Don't let it go over 10,000rpm
Change the AS atomiser to the next biggest size
Try 1/4 throttle again. When the AS is rich enough to be 1000rpm less than the maximum. We have some minor progress.
Edit: This is jetting lean to rich. Don't ride it.
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@ginch avatar
UTC

Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and '66 Blue Badge Smallframe
Joined: UTC
Posts: 8610
Location: Victoria, Australia
 
Veni, Vidi, Posti
@ginch avatar
74 Super, 75 Super, PX project, LML off-roader and '66 Blue Badge Smallframe
Joined: UTC
Posts: 8610
Location: Victoria, Australia
UTC quote
Jack221 wrote:
Nice set of needles. Keeping generally as it is, AS262, 52 pilot and remove the main jet. Without the main jet it's easier to see what's going on.
Set the mixture screw at 1 turn out. Lean.
Put in the X5 on clip 3.
Mark the throttle grip accurately in 1/4 increments allowing for the slack....
Thanks Jack. I'll have a look at this on the weekend.

The X5 is richer than the X2 by the looks? Same spec except thinner at 2.46 rather than 2.5?
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