Modern Vespa

I'm fairly confident the CD only refers to drag through the air rather than the friction of the tyres. Otherwise, nice work!

So let's chat a little about jetting.
Now - I know what you are going to say - and your right.
Sure C man. Easy for you to say. You've got a Smart Carb.
And while that's true - the basics are still the same.
Anyone can adjust a carb.
But figuring out which way & what part of the throttle you are trying to adjust is the challenge.

So having just installed a stainless steel version of king kong's lower intestine for an exhaust, now seemed a good time to refresh myself on my tricks.
Not that I am a world renown expert - more just sharing a few things I find helpful.
At the end - I have a question as well - if a certain someone is reading.

Couple days ago - I posted a pic of my plug and piston top.
Figured it would be a good reference point.
Plug looked wet and was the color of dark charcoal.
Too rich!

But as I noted at the time - the last 1/4 mile I drove was home from the local shops - trying not to make a lot of noise.
Maybe that was more an indicator of my first 1/4 throttle than anything else.

What's that?
How can just 1/4 mile really change the plug color?
Well - that's kinda the point of this post.

I frequently see other NSMVers posting pictures of their shiny new plugs they put in to get a read on jetting.
They always look horrifically lean - like - Pantone # oh shit stop riding immediately gray.
I mean - like grandma's private bits gray.
Ok - ok - I think you get the point.

But I maintain - you cant really tell anything from a new plug by just looking at it.
And chopping new plugs in half is my least favorite sport.
So for a really quick read - you need a plug with color on it - and
perhaps counter intuitively - the last thing you want to do when starting to re-jet, is put a new plug in.

The other thing I like to do is have some weight on the scooter - and do my 5-7 second run at a single throttle position - leading up to a parking lot.
This way - I pull the clutch, hit the kill switch, and coast in to the parking lot. This gives me an instant read on how that throttle position is jetted.

Oh - and one other thing.
I always shoot my pictures in fresh daylight.
No flash - that changes the color completely.
For fun - I show the same plug below shot in daylight and in my shadow for an example.
Kinda brings the point home about shooting in daylight consistently.

Oh - and that question (jack...)
So you've said that a tuned motor tends to be linear on mix.
And that it tends to get steeper.
I would say I am experiencing both.
The question: I am (surprisingly) getting a little hitch in the 4700-5500 rpm range. EXACTLY where the pipe kicks in on the chart.
Its not a backfire.
Its not a hiccup.
It is subtle - but it is there.
Imainge a single 4 stroke moment as you pass through that RPM.

Any ideas? Christopher - you would be right in the juice with this pipe. Tested it myself on hwy today. It is a bull at that RPM in 4th.

Bridsnest -your on 10 on your guitar - where can you go from there? where? Oh! well - I of course have more of that also. They suggest .3 to 1.0. Surely my sidecar puts me at the top of that range? Good to see you in these parts.

plug looks great on second one tweaked for 1/4 throttle.

Now that I know you like going on Mulholland Drive with the leaner sidecar, I'll be looking for you on this channel:
https://www.youtube.com/user/rnickeymouse

you know you've made it when you pop up on his feed. Just don't want to see you be on one of his blooper reels!

I'm sure that drive is incredible on a tuned vespa. Some day I will make it out there on one of mine.

https://auto.howstuffworks.com/question497.htm

Calculating drag. Doesn't look toooo hard....

Wadda you mean?
I did calculate it.
I read that its between .3 and 1, and I calculated that no scooter without a side car could have more drag than I do - so I gave it the max for a non-sidecar scooter!

That can be expressed in an equation as so: + = , where is the expression on my face and is the expression on my dogs face, when the pipe kicks in.

Drag equation gives much more of a chuckle than the usual science.

Ok dip. This happens...... but usually means timing is too low. Doesn't mean "I've set it precisely to the number in the instructions so it must be right". It means your eclectic assembly of parts requires more timing. Increase the timing and increase the jetting at this point (or bad things happen) and it will glide right over the dip, into the howling exctacy bit.

Thanks Jack.
I'll play with timing - and juice one metering rod richer.
I'll start with 2°.
Struck me today that its not only the pipe that is kicking in at that RPM.
Went and snuck a peak at the SIP curve.
Looks like it starts to retard right there as well.
Perhaps I am getting some weird resonance thing by aligning all that stuff at once.
We'll find out.

Well that's a coincidence. Timing starts to retard exactly where you have the dip. Highly suspicious. Standard answer, up two degrees and try again.

For the record, where is your static set?

If you had a kytronic you could just change curve with a click. Just saying.

Going to be an increase in max power too*. Doubt you will be disappointed about that.

Edit: * If it doesn't blow up

Just saw this listing and thought maybe i'll join you in the sidecar club but at that price.. i'll pass! It's the most expensive Bajaj ever!

https://newyork.craigslist.org/mnh/bfs/d/new-york-mobile-beverage-cart/7289382196.html

Although if i could swap the coffee for some beer.. it would give new meaning to drinking and driving

Gotta keep my eyes on the fine print...
Best I recall - I have it advancing to ~ 18° @ ~4KRPM(variable)
In theory anyway.
It can be tough to strobe these things and I cant bring myself to do that to my neighbors.
Yet.

For this adjustment - I will adjust 2° at a time using the nicely etched marks that SIP/Vape provide. No strobe.

I will use temp/plug/piston top as my indicators once I start advancing.
1. Heat should move up to the head - so temp gauge should be useful.
2. I Photographed the piston top so I've mapped the previous damage. Any new ping marks will mean I went to far.
3. Looking at plug for any signs of aluminum balls. This is one time its not good to have balls.


Shot pics of the piston as baseline to map any existing ping damage.
Twisted the stator 2° counter clockwise.
And set out to return 50 pounds of drawer slides in the wrong size to Amazon.

2° didn't knock out the 5500 issue.
Its COLD here so it was hard to get and keep temp on pipe.
Not sure I felt any noticeable improvement - hitch is still there.

No pinging - and only managed to creep over 315° once - while hammering 4th gear on very slight incline on the way home.
Plug and piston top appear untouched.

Do I put another 2° into it?

*Edit - Swiss! Worth every penny of course... 🙂.

Learning lots from your plug chop post.

Also, nice photography light/shadow lesson!

Mental imagery of Grandma? 🤮

Coming in a bit late, but I love your lovely dremmel drawer! Food for organized souls.

And now, back to math and curve graphs and other advanced scooter nimbo jimbo....

Have fun.

18 degrees @ 4000 and now is 20 degrees. Keep going. 2 more.......and another 2 more. Possibly 2 more after that.

Keep jetting up so wot stays under 300F max. Can lean it out when it's safe to do so. If the jetting has any weakness it will ping. Playing with the big boys now.

If each 2+ has a Dyno run it will make good science.

As long as the plug doesn't start to look Grandma's.... or develops acne. And jetting stays rich, the worst that can happen is it won't rev right out.

Well - let's just say - the didn't work out exactly like I expected.
Before I advanced any more - I did a single speed run.
Normally I run 2-3 in a row.
But this time - I was - well - only able to run one...

Few observations/comments.
- The 2° I had advanced - had not knocked out the miss yet
- Not sure I will be able to go 2° additional. Even with richer rod it seams the pipe resonance ate my rings with this timing?
- Surprised by rings dying while not pinging. Advancing should have moved heat to the head and piston top. Retarding should move heat to the exhaust. But this is classic exhaust heat melting rings I think.
- Looks exactly like SoCals.
Same effect - just came off throttle and bike seamed to just shut off - like I hit kill switch. No drama - no back tire squeal - I had almost come to stop when it just "turned off"

How do you set the idle on that smart carb? Seems like if it happened after a hard wot run just as you let off the gas, then its the idle too weak?

BTW.. sucks as you know. and Im continually amazed your positive outlook when this stuff happens. You keep plugging away without being fazed and its incredible.

Ha - thanks.
Fly close to the sun - wings will get scorched sometimes.
(mixed some metaphors there for certain).
¯\_(ツ)_/¯

I don't think the damage happened just 'cause I let off the throttle - tho I may have gone from way to hot too way way too hot.

Think they got chewed up at high RPM - tho can't be certain.
Assume that exhaust port was lightening hot already?
For fun - here is the video of it occurring.
The sound you hear is a digital one of the ignition firing - not an exhaust note of course.

Have to travel - so it will have to wait for my return to get a closer look and rehab.

https://youtu.be/VTmRMwnesEI

This one needs a post mortem. Those marks look more like something got loose. Not enough melting going on for detonation. Plug looks totally fine. Will be able to tell more when we can see the side.

If still at 20 degrees @ 4000 timing, then it wasn't that. Can run 10 degrees more than that @4000 without this kind of damage. Something up with the carb or the last ring just broke. For both rings to go at the same time it would need piston melting to hold the rings in.

Spare piston is handy. And still the MHR on the shelf too.

Edit: just saw the video. Doesn't help. If there's melting then it's the carb. All you need before going away.

Suxx is not a strong enough word. Sorry to hear about the meltdown.
Power output is fantastic though! As swiss pointed out, your upbeat outlook is amazing!

I've melted the side of my piston by the exhaust port and the rings never broke. When I looked down I saw the CHT climbing. That's why I have an EGT now, reacts much faster. I still have the same piston and rings installed. I cleaned up the smeared aluminum and freed up the rings. I want to see the side of the piston by the exhaust port to see if it's melted and smeared aluminum.

The drop in power is a little disappointing.

I'm also voting for Something Came Loose.

That looks similar to what my VBB looked like when the gudgeon pin circlip popped out and chewed things up last summer.

That dip might be design inherent, look at this graph.

http://www.pipedesign.de/auspuffanlagen/px-125/daytona-177-goldline-neu.html



P200 seems to have it also

http://www.pipedesign.de/auspuffanlagen/px-200/daytona-220-goldline-neu.html

Wow you guys.
Well - those response are more unexpected than the motor blowing up - which lets face it - was a pretty low bar.
I noted some months ago - I have some piston slap - was getting kinda nasty.
Perhaps that's involved.
Lucky for me - we have SoCal's ring melt somewhere in the archives - so at least we can compare

Editors note - SoCal - my apologies for bringing up bad memories. Bad behavior Really.


I'll hold my opinion then until I can pull it off and get a closer look at the side and piston top. Im frankly not sure there are any ping marks at all - cant tell with camera if its ping or shaved ring material sitting on top.

I will say - the thing that just didnt make any sense was - I was not seeing any heat gain on my CHT gauge. My posted pic Cleary shows I turned counter clockwise 2° so if it was going to get hot - I woulda thought I could see it there rather than putting more heat in the exhaust.

Thanks for the comments.
Helpful for consideration.

Jeez... tough crowd... you melt a couple of pistons and suddenly you're "Mr. Bad Example"

Carry on

Christopher - It happen right where the pipe came in to the curve turning up - not during the area where the power curve was flat. In fact - at 4K-4500 rpm it cruised along really nicely/smoothly.
But its good to see the my curve is not so different and its interesting to see how some lower timings have that power band coming on a bit earlier.
Thanks!

It was more of a "miss" or momentary 4 stroke feeling.
Right at 4700 to 5500 range.
Its possible that the advancing of the timing had knocked out the 4700 end of the issue. Im not sure. I didn't feel it there when I tried to make it do it this morning - on my way to the speed run.
But on the speed run - I definitely felt it somewhere in the 5K's. . Hahaha. If the guys are right - it might not have been timing related. So basically - it may turn out to be just a drive-by elbow I threw for no reason at all. Lotta years of hockey. What can I say.

Catching up on this thread, makes for great lunchtime reading material...

And keeping your thread warm whilst youre away...

Making me reminisce about the bullet 220 HS I had on my rotary setup... definitely one fat exhaust... love what pipe design come up with, quality product...

Hope you get to the bottom of the rings/melted piston saga..!

Here is one hot piston, high bake on it's way to broil. I think I lost some compression, will see later this year after getting it dialed it.

What did the cylinder wall look like?

Not bad, the piston donated some aluminum to the cylinder wall. Added a picture of it to the previous pictures.

Look on page 3 of this thread for more pictures.

2007 Stella P200 Motor (installed Polini box exhaust) (Page 3)

Thanks! Your journey with the scoot makes for good reading...

Ah the good old TMX... when I had it on my rotary setup, I had a crank explode on me because I went too lean with the pilot and needle, on a hot day, at WOT... lesson learnt the hard way

Just catching up on the melt show. :-/

Drag to see bad news. As others noted, your attitude about the set back is pure gold. Tips cap.

I suspect you will have it sorted in short order.

Now this is nearly as concerning as you vacuuming the garage when there's piston rings to change.

This "miss" sounds just like lean jetting does. Usually a weak pilot jet (yay Swiss) and\or lean needle clip on a normal carb.

Fingers crossed for melted in rings. Clean up new rings and running before lunch.

Need some seriously richer jetting for next time out. If still over 4 degrees under, a normal carb could need a 20 point upjet.

btw, didn't mention it before but your engine sounds amazing in that video.. up until the unfortunate event. Is that the smart carb or just how it sounds regardless of carb?

I get off a plane and the diagnosis has flipped.

I had run it on a richer jet but felt or was too fat.
Plug certainly doesn't say lean - at least at WOT.

Anything is possible I suppose.
Camera down cylinder showed no aluminum on walls either.
Also- center of plug no pinging.

I've definitely had total ring failure - but I'm not sure why.
The failure - if jet related - was either WOT or idle end of metering rod.

Idle end should have caused a seizure not a ring gnawing?

Miss was at 5k range. If it was lean there it never saw that rpm when it failed. I was at ~9k rpm then dumped throttle and braked.

All above taken together with washing machine piston slap - and new found ability to wind out powerfully to 9500- my guess is it vibrated itself to death exploiting the piston slap issue. What ever that was.

Autopsy next weekend.

Since we are bench racing - and I love to get out over my skis to find out I had it all wrong - I will double down on that one to maximize face plant.
Also - traveling and nothing else to post.
🙂


So here are some pics from prior posts - pulled together for a "best of" diagnosis from afar.

After having a think it's likely both happened. Something could have come loose damaging the crown. Scaring looks too much for detonation but could be. To jam both rings in at the same time it has to have overheated. Even if one ring broke and the other stuck in, it still overheated.

On the plug the electrode has no darker line, which means lean, flat end looks grey, which means lean. Some black dots here and there, which mean detonation. And are a precursor to acne. I'm calling lean. Easy to be rich at the bottom, rich at the top and apocalypse in the middle.

Timing was nowhere near advanced enough to be the root cause.

I'm thinking you'll get away with new rings. Might not look so pretty but it will do the job.

Alright - well - next weekend I'll pull it and we will see up close how things look.
Im not convinced that the top of the piston has any damage at all.
That might be fragment of ring sitting up on top - but just guessing.
We will see when I get in there.
Kinda interested now to see what I see.

Hey - can you clarify this? Not sure I understood where/what you mean.
Fire an arrow on top of that pic if need be - I'm interested - just cant decipher.

* Edit - Has anyone else had bad piston slap lead to a ring eating event before? Is it a thing?

Plug electrode would have a dark base and lighter tip if all running well. If it looks hot all the way to the plug body without the mid dark transition where it was cooled, then it's overheating.

Piston crown has too much silver showing. Should be 90% sooty black with gold wash spots for perfect. With the fat expansion there is less ability to run as lean as you have been. I always run my main jets so I can feel very slight WOT splutter if briefly opened up while riding around at 250f. When holding WOT long enough to get warmed up to 300f, the splutter is gone and fully on the power.

You have even richer rods for next time out?

A whole drawer of them (27 & 26 in stock).
Smart Carb guys says the EK27 has been the most popular with the German tuners.

Had pretty bad piston slap on an vertex malossi piston. Swapped it out for a new piston (crankshaft exploded and scored the piston) and it seemed to had gone away (old setup)... not sure if it was the wrong jetting or a badly balanced piston that was the problem...

You just had to show all us organizationally challenged hoarders that beautifully organized drawer of smatcarb goodness, didn't you? Ha! Even with anti-slip material lining the bottom of the drawer.

Nicely done!

Ok - as I'm sure you all remember, back on page 20, I noted that the brass bearing seat on the clutch side of the motor, sat askew by about .5mm.
Though I'm sure you have it visualized with crystal clarity - I am reposting that pic below for the few that might be fuzzy on it. More about that in a moment.

where we last left off - my motor seamed to have eaten the rings - or something- and was not very happy about it.
Opinions abound - from garages and couches around the globe.

Today, I stepped off the plane at 3:00 and was in the garage at 4:00 to get some answers to our questions.
Let's take a look shall we?

First up is the video - only because I'm too lazy to figure out how to post this after the pics. Have a look - shows play in the connecting rod. Suspect this is related to my askew bearing seat if I had to guess at root cause.
Q: do other tuners on here see this when they take their motors apart - or is this way outa whack? Weigh in!
https://youtu.be/se711FYzJr4