Modern Vespa

Hey everyone, I'm Jon and I have been lurking/reading for a bit to try and learn more about my scoot. I figured it was time to post and introduce myself and my ride.

A few years ago a client was nice enough to give me a '78 P125X after I saw it in their garage and commented on how cool it was (shown below with my first love). I was told that it needed the fuel tank cleaned out, a new fuel line and a carb cleaning to get it going. Knowing nothing about Vespas, I did as instructed and sure enough I got it running.

I have been fixing small items like broken turn signal lenses and wires, replacing rotten rubber bits, and trying to learn how to get it running right. I know nothing about 2T engines but have been able to get the scooter running well enough to ride around town a bit. Add to the mix that this P is not standard anymore and I'm even more in the dark. The previous owner made the following modifications:

-Polini 177cc kit
-SI24/24e carb (jetted with 160AC, BE3 mixer, 120 main & 55/160 idle)
-Autolube delete (running 2% premix)
-What appears to be a sito plus exhaust
-I can see from a sticker in the glove box that new gears and clutch were installed...but no specs given

The first question I have is, does that jetting seem right for the Polini 177cc? I am fuel injection guy and do not yet understand carbs...but I am hoping to fix that.

Second question, I believe I experienced a soft seize yesterday after pulling a sizeable hill...the engine sorta stumbled and then cut off as I was riding down a flat road just after the hill. The wheel did not lockup (that I could feel). The piston is free and I still feel compression pressing on the kick starter...but I'm assuming the next proper move would be to dig into it and see what the damage is?

Any guidance that you guys can offer would be appreciated, this is all still very new to me! Thanks in advance and sorry for posting a novel!

Welcome to the forum. Nice fastback. Had a sky blue 72 squareback ages ago. With the backseats down and flat, it was hands down the most efficient hauler of cargo ever made. Pancake engine was bulletproof too. Loved that thing.

You're jetting is in the ballpark, depending on what other modifications the prior owner did to the engine. Wouldn't hurt to pull the head and take a look down the barrel. What you experienced might've been a fuel starvation issue rather than a seize. You might want to double check the routing of the fuel hose. A fast flow tap would be a good add on.

The engine is not hard to work on, especially if you've had experience with VW 's. Lots of helpful folks here if you have questions.

Thanks for the help! I can definitely double check the fuel line routing and the fast flow tap sounds like a good idea. I would rather it be fuel starvation than a soft seize. I'm hoping to have a little time this evening to pull the head and take a look at the cylinder.

I'm a big fan of the air cooled vw pancake engine. That thing has been a reliable engine for about 14yrs now...hasn't left me stranded...yet!

Popped the head off for a look. What do you think? I can't feel the marks on the exhaust side of the cylinder but I can feel one on the intake side. Doesn't seem great to me, but would love to hear what others think.

The jetting is close to where it should be in my experience with the same set-up. The cylinder looks totally fine. I had numerous soft seizes on my polini 177 kit back in the day and it continued to run fine despite more serious scuffing. I'm not sure you actually soft-seized. These engines can take abuse, until they can't.

Thanks Yackee, I appreciate the feedback. I'm going to follow socalguy's advice and get a fast flow tap and check that fuel line routing isn't an issue. Hopefully I just bungled the fuel line setup... definitely more used to having fuel pumps, injectors, & pressure regulators on my rides!

That cylinder Does not look copacetic. Will it work? Maybe. I'd want to know how the piston and rings are faring.

In other words, pull the cylinder to inspect the piston and rings?

Depends on what you want out of it. Looks like the head was leaking not good. Jetting may need some adjustment generally a 160 air corrector on the main jet stack is no bueno for kitted engines but could be more than that. Once you have grooved the cylinder it will continue to be prone to seizures. The rings might not be working correctly either. You could probably bolt a go but the outcome will not be good.

Hibbert, thanks for that bit of wisdom. I would ideally like for this scoot to be a reliable weekend fun ride. I recently had to move out of my workshop and my VW had to go to storage but the P fits in the shed here at the house.

Regarding the air corrector, are you saying a 140 would be more appropriate? As to the head...is that simply a flatness issue? Or something more?

I live in a very hilly city and would hate to be pushing this thing anywhere unexpectedly. I guess the big question is, does fixing it mean a new 177cc kit or more than that? I don't mind fixing things, but I just don't know that much about these machines.

My buddy's Jeep Cherokee with a 4.0L inline 6 cylinder that 2 cylinders that look worse than that runs great, stays at perfect temp, and gets road tripped somewhat regularly. Having seen that motor, I could see how this could be ok...but I also understand they are different animals.

Thanks!

Heat is the enemy here. Hard to say if it's just the head leak or possibly other factors. The head needs to be flat they can warp potentially if not torqued properly it's common to true them on a precision flat with Emory paper.

There's nothing wrong with that cylinder. I'd hone it and run it. It's got thousands of miles of life left in it.

The piston probably has some scuffs and scoring. Those can be cleaned up too.

Swapping your 160 air corrector for a 140 will reduce the volume of air fed into the mixture,
which will result in your engine running a bit richer and cooler at speed. You'll most likely need a smaller main jet so get a pack of jets that covers a range of different sizes from 115-125. Finding the one that runs best is largely a process of trial and elimination.

The head isn't a big deal. Looks to me like it just wasn't torqued down enough. The mating surface can be sanded flat on a plate of glass or a countertop.

Also make sure you're using the right plug. Polini takes a short reach - NGK B7HS or equivalent.

Some folks will tell you to just buy a new top, buy a new carb, replace everything, blah blah. Don't listen to that. You'll never learn anything about these engines if you just slap parts on.

And if you're expecting that you'll never break down you've got the wrong hobby. There isn't anybody on this forum who hasn't had to push their scoot. They will run pretty much forever in stock form, but when you start putting kits on you start compromising. We try to make them as reliable as we can. Finding the magic formula for your scoot is part of the fun.

Welcome to the game.

Thanks hibbert and socalguy! Socalguy's approach is what I was thinking about trying first, if it doesn't work out, I'm only out a little time (not a big deal). I will definitely get some jets ordered up along with the 140 ac, and I am running ngk b7hs on the p.

I definitely want to learn how these things work, but also want to learn when it's time to replace parts. Fwiw, I fully expect to break down and have issues, but I want that to happen as little as possible!

Thanks again for all of info and feedback guys!

Anytime I see the oil injection deleted I view at it as someone does not know that they are doing as they work just fine -

I personally would drop the engine and remove the cylinder to do a full inspection, no fucking around MV style. there you get a very clear view if what you are working with on that setup. Cleanup the cylinder and maybe new piston/rings- just depends how bad things are in there.

For god sakes, put the oil injection back together.

The bike didn't come with any of the oil injection parts. To be honest, I don't even know what all I'm missing. I will look into what it would take when I dig deeper into my issues though.

Is it that much better than premix?

Thanks!

there's nothing wrong with premix, I've been at this for 17 years and still not owned an autolube scooter yet. however, if it's there, most will argue the system is well designed and that they are usually worth saving for ease and reliability. I'd not make it your top priority to get it back on but you can certainly think about finding the parts and adding it back on leisure time.

This is the approach I'm planning to take for now. I did some reading about oil injection at lunch and it sounds like a good thing...but, I have money to spend elsewhere at the moment! Thanks sdjohn!

Is there any truth to oil injected carbs getting false air if not sealed properly?

If you have the engine dropped to inspect the cylinder & piston, that would be the best time to inspect the oil injection system. it very well may be all there but blocked with a non-oil gasket or other. The systems are very robust. People who do not understand what they are doing get in there with their hands and start fucking with them one way or another.

Heard. Will take a look at that point and make notes about what I have & don't have.

I read that all the time, and my opinion is that sealing the oil tract serves more in keeping contaminants out of the system than avoiding "false air" issues. The oil duct does end above the slide, after all, where the air still flows relatively freely from the outside. Totally agreed. Many people get some kind of engine failure, and blame the oil pump by default if they're unable to find the actual culprit.
Not only are autolube systems incredibly reliable; they dispense the correct ratio of oil/gas into the cylinder for every situation (between 0.8% and 2% from idle to full throttle). A premix engine will be dispensing the max amount of oil regardless of the rpms, overfeeding it oil most of the time, especially when sputtering around town.

I appreciate this info Frank N Stein!

I looked into the fuel starvation suggestion a little bit yesterday and found that my fuel tap was clogged. The annoying thing is, I had checked flow just before my last ride and it was great. The tap was clogged with black debris...not too sure what it was. I expected to see rust particles coming out not mystery black stuff. Anyone know what it might have been clogging the tap?

From reading on here and watching videos by Chandlerman and FMP, I saw that some folks drill out the float bowl passage to the main jet. My passage is still the factory size. Do you guys suggest enlarging the passage (2.5mm according to FMP) or keeping it standard? It seems like something I should do based on what I've read, but figured I would confirm before proceeding!

Drilling to 2,5 mm can't hurt whatever the engine; it's encouraged when dealing with a kitted engine prone to fuel starvation.
From the float bowl and from under the jet stack, paying attention not to drill too far, obviously.

Got it. Thanks for that! Will probably knock that out today while I have a little time.