Modern Vespa

Good morning,
First off thanks to everyone for all the help and entertainment so far.

I've got a '58 150 VBA engine with the following.
Pinasco iron 177 unmodified
24/24 carb with 55-160 idle, 160ac, BE3, 116 main
SIP Vape static timed to 18 degrees
SIP Road exhaust v.1

After a year off I'm excited to get back on the road[/img]

I'd drop the air corrector to a 140 and up the main to a 118 or 120 to start out, then walk it down from there.

The 24/24 is also overkill and will probably make it harder to jet in, especially at mid-range, unless you hogged out the intake a little and increased the intake timing. If you have a 20/20, it'll probably run better with that.

And make sure you have a CHT before you start to thrash it or do any long WOT runs.

All of this times 3!

You'll be lean at 116, and CHT for sure to monitor those temps.

Looks great!

A 2 port 1958 engine with a mild 177 kit. I'd say a 116 main may not be far off in an unmodified 24/24. It's what you'd find in a stock PX200, which in my mind must be slightly more powerful

As a big fan of superclean stockish looking motors, I love what you've done here but what is up with your rather rakish kickstart angle?

His kickstart lever is VERY excited to get going!

^^^^
hahahaha...

wow that'l foul the cowl!

Thanks. It's just on there so I could time the engine. Easier to manipulate. Good thing about a fully splined shaft.

The case has been modified to fit the 24/24. I've got a Mazz cut crank in there but not sure of the timings. Have to look at the box later.

This crank
https://www.scootermercato.com/Scooter-Parts/Crankshaft/131897CUT

A CHT. Can't I use my laser thermometer? Geez I don't have turn signal and don't really want to double the amount of gauges, lol.

My $.02.

cht is a good gauge to have.
lots of guys on here like to use the trail tech.
looks like there are some new offerings too - from poling or pinasco - idk.

In carb - I ran a 24/24 no trouble with similar setup.
really enjoyed.
you can make those little carbs scream.
CM's suggestion to drop the air jet down a good one.
Think we covered the why's previously.
Think of the AC as just bracketing your main jets.
160 means perhaps 128-135 mj
140 means perhaps 120 - 126mj
120 means perhaps 114-118 mj
(above just for example - they are rough est).

But your carb only will flow about up to a 120 without drilled float bowl hole.
So do yourself a favor and use a smaller AC if you want to make sure your MJ is doing its job.

Are you running with 8 or 10 inch wheels?

I've got the modifications done to the 24/24. Drilled bowl, bigger inlet needle etc.

Oh and I'm running 8s.

Yip... you WILL blow it up!
Enjoy

Run a 140AC, and bump the timing up to 20°.

Thanks guys.

So finally got back on the road with the changes in the jet stack. Finally revs(edit: stumbles in third I apparently don't know what thing mean) in third. Also installed a CHT. Went for a run this morning. About four miles in it seized hard. Temp never went above 250. In my other thread about the way the engine sounded(yes past tense) the little unidentified sound I noticed went away about five minutes before the seizure.

So will pull the engine for the umpteenth time.

Anyone want to guess what I'll find inside?




Glad I just finished the trailer.

I'll take bad things for 500, Alex.

Aluminum smeared on the inside of the cylinder over the exhaust port. The rings melted/stuck in their channels. Too small a main jet.

That's a bummer. I feel your pain. Been there more than once.

i've never seized a 2-port Pinasco 177 at touring speeds. similar setup but always with a 20.20 carb. The 24.24 is not necessary and i reckon probably not a great choice.

now i am intriqued at the aluminum Pinasco 177 that comes with a 2-port sealing gasket. . . .as well as the aluminum Parmakit 2-port 177. The aluminum Pinasco is not much more $$$.

Oh but Chandler, I'm revving out in third which means too large a main, does it not? It also happened mid shift if that throws some more intrigue into the mix.

Too rich would be stumbling instead of revving out in third.

The good news is that the pinasco is tough as hell.

Despite my best efforts, I only managed to kill my cast iron Pinasco 177 by raising the exhaust port too far. Not even eating a wrist pin circlip could kill that jug.

I think I put a random DR piston from the parts pile in it after that and just kept running it.

^^

agree, if you were winding out the top of 3rd then you were likely lean.

hopefully you'll luck out and be able to salvage it.

run 'em rich; otherwise you gonna be poor!

OK so I meant stumbling not revving out. I had the definition wrong. Revving out as in running out of revs.

At least I have a chance to try out the engine stand

I'm with Gick. No way an unmodded, cast-iron 2-port Pinasco was running lean with a 120 main jet unless it had a massive air leak.

Are you sure it was the top end that seized and not the clutch or something in the transmission that let loose?

Won't know the answer to those questions till Saturday.

Keep the faith!

Just rebuilt a 65 VNB for a local. 2 port cast iron Pinasco with stock clutch, 24/24, Vape, Road 2.0. Clutch blew on the bench. Tired old clutch basket couldn't hang with basic revs.

I concur.

maybe the timing was off enough? but I don't see how a 120 locks it unless it was a confluence of events like poor fuel flow + rolling off at just the right time + no air filter or something.

First off - sorry to hear. That sucks - but your gonna end up better at some point with this - and that much more expert.
(IK - not much consolation).

So - usual questions and a few comments...
- Is the carb float hole drilled? This will change the size of main about 6-10 points richer when it is - so some of the comments may be altered by that.
- You may have seen slightly higher temps than you realized - it seized after you came off the throttle - so I'm going to say heat seize. When it happens - it can be a very quick spike. Do you have a recorded top temp?
- You may find that your ring gap was too small. Did you measure ring gap when you built?
- Your "120" main jet COULD be smaller than it should be.

The thing about iron is, it expands slower than aluminum.
The thing about aluminum is, your piston is made of it.
Piston will expand faster than cylinder and can be unforgiving if piston size or ring gap is not right.
Aluminum cylinders are far less likely to seize for this reason.
just some data should you need/choose to replace the cylinder.

I prefer to jet the carbs with smaller A/C's - as per Chandler.
This allows less chance for restrictions un-related to the main jet from being problematic.
(It also moves you down in MJ size)

When you open it - look to see if you have skid marks that align with all 4 cylinder studs. If yes - it was unquestionably heat seize - and that's my guess.

Btw, love that trailer.

I thought timing, too, but my final answer is still "too lean." Now we're just working out how. If something was prevent adequate fuel flow, then it'll eventually lean out and fail like you're describing, and and four miles of thrashing could be about the right distance to do that, too.

you're right. timing would more likely hole the piston, or just beat the edge of the crown into failure.

what if: just down on fuel flow + too lean idle.

JRA, building heat but not too danger zone, come up hard and roll off snapping the throttle closed and it goes lean. zip.

I'm in the too lean camp with Chandler.
Pity me for having to camp with Chandler.
He wears his doc martins in the tent!

Anyhow - the clue for me was the seize while shifting.
Temp spikes after the hard run - as fan speed slows.
Iron's fave way to seize.

Rings won't be broken - just welded in position so they can't seal.
Since we are playing the guessing game...

This (as the kids say).

also, somehow he sleeps in the nude with them on.

he claims it's a feature, not a bug.

Hey Grumpnut, how about a few more clues?

Does the clutch still work?
Does the kickstart operate?
Can you roll the scoot with the engine in neutral?

It's the velcro seams on the pants. They're my secret weapon.

Hearing good things about the Parmakit.

A closeup of the spark plug will provide more clues.

Kickstart is locked up solid
Walked it quite a ways in neutral. No weird noises.
Clutch, well, it went into neutral. Didn't pursue since the kickstart won't budge.

I'll do my work and report back.