Modern Vespa

I got both the GL and the Smallie out over the weekend, which gave me some good comparative riding. The GL is obviously not as fast, and feels a lot heavier than the smallie. I noticed the weight of the engine more, too.

Now back to the smallie...I pulled the head, thinking I was going to install a screw in CHT sensor and discovered two things. First, I have lost my M10 tap. Second, I'm still way too lean on my jetting.

I have basically no wash and am trying to burn a hole through the piston . I upped the main from 170 to 180 and it still revs out, so I'll go up to a 185 next and try again.

Meanwhile, I made turn signals a priority and fabricated a bracket for the rear signals, then converted a VBB style handlebar switch to use the off/pilot/headlight switch for turn signals. I was able to do it by just cutting the connection from the switch to the headlight and bending that ribbon over to attach the power in.

I didn't get the front turn signals installed because I ran out of time, but that's just a matter of bolting them on and splicing them in.

That's not pretty, looks like you're going to need a new piston.

Yup. I'd like to make sure I have the jetting dialed in first, though, so I only have to so a new piston once.

Woah……

Can't be just lean, that looks like too much advance for a piston beating like that…

What's your squish like now?

When the main jet starts to get way out of step, it's not the main jet that's the issue. This is primarily carb adjustment, seen it too often.
It's one of many things, usually these three though; needle taper, atomiser, float level/weight......
What carb is it? And what are all the jets?
As it is ride without any main jet and you'll be surprised it's not so different.

I think it's a pwk34 if my memory serves me right

Correct, a Polini PWK. Same as the 30mm I had and never got to set it up right. It was either running super lean or super rich. I too melted a piston on my 221…

As others have already recalled, it's a Polini PWK 34. I'll have to go out and look at my board to get the exact jetting, but I've run the same model carb with basically no issues on my GL for several years now. I'll try removing the main and see what happens.

It's a little boggy at 1/4 and 3/4 throttle, but pulls like a racehorse on the power curve at 1/2 and WOT, just the dip where it stumbles at 3/4.

The motor doesn't run hot, but I also haven't been thrashing it too hard until I figure out what's going on with it.

I've considered retarding the timing a degree, too. I almost went ahead and did that when I saw the head, but given that the piston has basically no wash on it, I upped the jetting instead. I'll go ahead and do that when I'm back out in the workshop.

I'm feeling a little lost on this one at the moment, though. Like there's some fundamental I'm missing here. I'm going to double-check float height. I wish I had one of those transparent float bowls right about now.

You're running the vape sport ignition right? Timed all the way to approx 8k rpm (know you don't have a rev meter… guestimate…?)

You'd know about float height… you'd feel it.

But your piston pitting started before you heat seized…

I have my tach working, but need to play with the adjuster on the Koso filter, because it reads about 1k low at running revs. It's also too slow to keep up with the motor when it really jumps on the power, but that's a different story.

And I threw a Runleader tach on that I stole off the VBB, which is how I know the new tach reads low.

But as to the ignition, yes it's a Vape Sport. And while I timed it for peak power at 8,000, that should actually have me potentially too retarded at 10k, which is where I redline based on speed and comparing to my gearing calculator.

Squish was just under a millimeter, which is spec for the kit. And there was no pitting on the piston when I seized it or I'd definitely remember that. No signs of any detonation, either. Just too much heat, I think. Which is weird since temps have looked good.

All very frustrating, to say the least.

No to mention that I'd have gone ahead and ordered a new piston along with the master cylinder kit if I'd know.

What are all the jets in the carb and needle? Float weight?

I doubt anything you have done before has a powerband like this. And will need adjusting like never before too. The problem is what you thought was ok.

That dent in the piston although not worthy of replacing does mean the jetting is wildly inaccurate somewhere. With the no wash marks, it is most likely too rich in certain situations and too lean in others. This gives the illusion of rich safety, while still doing damage.

Timing makes dents around the piston edge and melts the plug. It may not be perfect but no sign of that.

Put the head back on, take the main jet out, warm it up. Leave it on the stand and go steady through some throttle positions and rev cycles to post up a sound recording.

Hey Chandler, I think you're reading the piston wrong or maybe confused what "wash" is. The lack of burn around the perimeter is too much wash ... an abundance of mixture is entering the cylinder through the transfers and washing the piston clean. That indicates a rich condition.

That focused burn in the center of the piston looks to me like classic detonation. I'm guessing its a timing issue.

Piston looks like the same pattern mine had…

Yup. I was totally misunderstanding how to read wash. Thanks for setting me straight Timing was my initial instinct, too, but there's zero evidence of detonation other than the damage to the piston crown. No aluminum spatter anywhere and the plug tip is black.

I need to go back to square one with setting up the carb on this beast, I think.

Also, current setup is:
180 main
KLK-4rh
45 idle

From here it looks exactly the same issue. Outcome will be interesting.

Was this what drove you to go back to rotary on your 221?

One of the reasons…

In happier news, I got the first round of slow down-fast parts today...

Ohhhhh, ahhhhhh

In other news, turn signals are installed and working nicely. I used a VBB-style switch I had lying around. I cut the connection from the off/pilot/headlight switch to the headlight, then soldered the DC in onto the headlight ribbon on the back to use the light switch for signals. Much easier than how I did the VBB.

I'm happy with how they work. I haven't even ridden it and already I feel safer on the road.

Here's a short little video of them in action.

Really strange to see an old small frame with decent lights. Good job.

Hearing it run, is less good. If set up for economy it's not so bad but if set up to be used as a weapon, the most likely is the diameter is several steps to big and/or clip more than a few mm too lean.
What other needles you have available?

Sorry to hijack, but just to help move the conversation along…

Needles should be usual suspects…

The BGM set, which includes:

HKJ, HLJ, JJK, JJL, JJM, JJN, JJQ, JJS, JLJ, KLK

I imagine this is the set most folks will have with a pwk.

I thought we'd already determined I'm not Most People.

I have a fairly robust collection of needles at this point and am not afraid to order more.

That's a fair few K needles… K tapers are too rich in my experience…

Fairly straight needles seems to work the best for vespas… don't know if it's the engine design/shape or the cylinder/exhaust.

For the malossi 210 and even now the egig, are using fairly straight and long needles.

Oh, forgot to say, something else is going on… 45, K needle and 180 is mega rich…

Now this is getting into the difference between carburetors. Any motor will run on a straight (single taper) needle but when the hp gets too high (~25bhp per carb/cylinder) the lower throttle positions go rich to keep the top end ok. To get over this many carbs have a power jet and other carbs use dual or triple taper needles. With PWK I suspect Chandler is just touching on the need for a power jet.

He should eliminate the variables one at a time. With a PWK first focus must be on diameter. The richness of the taper varies with the diameter, so this must be isolated first.

CM, if the smallie ever gets Dyno-ed and goes over 25HP, I'm flying to you and dinner is on me…

I haven't even GSFDyno'ed it yet, but it's already way over 25 HP. Lemme know when you want to come ride it.

Jack, would it make sense to just splash out for an air striker carb?

If that's going to be the easiest route to a successful setup, I'm not afraid to give myself yet another early Christmas present.

Video of the dyno run, and you can pick a restaurant!

The "brown pants" factor already adds a false sense of +10HP

I would set it up as is first and see how spluttery the bottom end gets. Might be fine. I like a small splutter that clears when opened slightly.

Just throwing this out there. All these kits are made with 11:1 C.R. or higher. That works on a go cart track or for sprinting. For pump gas and open roads I've found it doesn't work at all. The best improvement I've found for reliability is to lower the C.R. as low as you can get it, shooting for 8.5:1, though I don't think I've quite achieve that. 9-9.5:1 is probably as good as I've got by opening up the bowl only. Pretty simple operation with a drill press, a 1 1/2 inch flap wheel and a bunch of measure, removing material, remeasure........

I'm not going to change the compression. I don't think that's necessary.

I pulled the trigger on an air striker this morning, then had the smallie out for a taco & burrito run at lunch. I got pretty good GoPro video, including losing power when the carb fell off the manifold at about 70 MPH. Basically, it's pig rich across the range at this point. Temps never got above about 260, though, so so hope is not lost yet.

I'll cut together some video and post it up later. You can read the speedo and see throttle position in the video, so it might help with diagnosis.

Does it have a power jet? Could drill one into the carb you have. More fun and plenty of fire risk.

Higher compression is higher power. Kits are manufactured to the safe minimum. It is our job to make them unsafe.

Then I'm in the right place, because I'm excellent at making them unsafe.

As threatened, here's 6 1/2 minutes of grabbed out of my lunchtime burrito & taco run today. I left in the part where the carb fell off the manifold while on the highway, because I know that suffering is funny.

All this should be reported to the authorities as child abuse.

Wow. That carb needs work. Running awful. Plenty of potential though.

You're not alone. Carb fell off my Quattrini coming off a roundabout a few weeks ago. Very similar with no drama.

Really miss authentic taco's.

Who needs a carburetor; just get a big Pepsi bottle, a coat hanger, and a rubber hose to drip feed the cylinder.

Urgh damn… clutch slip…

Did you installed all 8 springs in the clutch?

Or just running the 6?