Modern Vespa

I have been searching for a classic vespa for some time but have not found anything suitable nearby. This Cosa which I think is a 1988 or 1989 I am open to correction.

I didn't know what to expect when going to buy it only that it was a project. The guy didn't speak English and I didn't speak French. Turns out it had the cylinder and piston along with lots of other parts in boxes. The bottom end didn't seem to have any play so I took a chance on it.

I have purchased a BGM 177 cylinder kit which I believe is a direct replacement with no jetting changes required.

When I compared the BGM piston to the coating damaged piston and cylinder I discovered they are the same size so it think it's a Polini 177 kit which was removed so I will probably need to look at jetting.

It's my first Vespa so any advice or input is very welcome!



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Very sweet. I wish there were more Cosa scooters on this side of the pond.

Exhaust and intake changes have the most affect on fuel consumption. If the displacement is the same, then I would suspect that the jetting would change very little. (That is assuming that the original jetting was pretty good.)

Document what you have to start with, because eventually you'll forget (I know I do). Then document each change, how it rides, and what the plug looks like.

Many are using a Trail Tech TTO Cylinder Head Temperature gauge to measure the spark plug temperature. This is a good indication of how the engine is running. If you can produce power and comfortable acceleration, without getting too hot, you at least know you aren't too lean.

Run it for a little and see what color the spark plug becomes. If it is too white, increase the main jet. If it is too sooty or the engine bogs then its probably too rich.

Maybe others will jump in with first-hand Cosa experience. There are also some jetting databases out there where others have documented what works for them. Those are good starting places, but I've learned to trust my own judgment through experimentation and examining the results of the jetting changes made. Sometimes it takes a long time to get it just right, just don't get discouraged.

Cosa jetting was on the super lean side (all engines) for fuel economy and emissions. When kitted it's necessary to ditch the secondary "cassette" type air filter box that's under the fuel tank and do a "kitted" PX jetting...

Nice! I never knew such a scooter existed, but as you probably know, 2 stroke Vespas were no longer exported to this side of the pond sometime in the mid 80's.

Looks like it's in really good shape. Welcome to the forum!

You will definitely need upjetting, it will seize very quick and those with the same kit will be able to give you bullpark jetting guide. Looks great. Cosas were dissed when they came out, very unpopular but today they are niche and ive always liked them. Not sure how the dual linked brakes work as never had the pleasure of working on one. Arent they automatic choke too? When the cosa came out it wasnt badged vespa, i think the suppliers in the UK started adding a vespa badge to the horncast to try and sell them via the name. Good find and i hope it serves you well.

I initially just wanted to bang a piston in this and get it running but after I had another inspection of the rotary valve with the airbox off I found quite a bit of swarf and other misc sh1t that I didn't like the look of and I have no idea where it came from. See the first image for a shot down the cylinder opening for the scoring on the crank/valve.

I checked the rotary valves clearance with a feeler gauge and it seems to be OK. I'm going to split the case this week hopefully and make sure there's not too many foriegn bodies floating around the crankcase, I should be able to check the clearances in here again, I don't want to ruin the cyclinder just because I wouldn't take the time to split the case.

I had a free day yesterday so I brought the carb into my apartment and stripped it down. The throttle was completely stuck on the bike and I don't think it has been run since like 2004.

The slide in the carb was completely stuck. It took a lot of petrol and levering with a screwdriver to free it up. I cleaned everything down in a pot with some petrol and a toothbrush.

I then decided to check the jets which were fitted. I'm not very familiar with how 2 stroke carbs work so it took me some time reading up what each jet did. The wiki on here was particularly helpful.

It turns out that there is the following jets fitted:
Air Corrector: 140
Atomiser/Mixer: BE3
Main Jet: 83

Idle Jet: Missing

Starter/Choke: 62

It's a Dellorto 20/20 SI carb just for reference.

I'm thinking the main is too small for a start and that I'm going to move up to a BE4 mixer. I have some time to decide what I need though as I'm not going to buy anything else until I split the case and figure out what else is needed.

Thanks all for the comments and if anybody has any suggestions on the selection of jets I need then I would be delighted to hear.

I have taken aboard all that's been said already and will consider a trail tech temp sensor in the future. For now I am going to just try to jet it rich and safe, I have a car so it won't be doing any long journeys for the moment.

One other item I didn't mention is the bike has an autolube system. Would anybody have any idea on how to check if this is functioning correctly?

Would you be able to direct me to any more information on the secondary air box? If I lift the tank is it quite obvious?

You will see it under the tank. Also the bellows will need trimming. And the slot of the cassette filter must be blocked...

BE5/AC140 and some big jet, im running a 24mm delorto with a 177. With my 24mm its BE5, AC140 and a 122 main. (thats with a road 2 and drilled air filter) If you are keeping the 20mm then the jet will be smaller than a 122. However, there will be much discussion about what corrector to use etc. There will be plenty on here with a 177 kit running a 20mm SI carb so just sit tight and somebody with the knowledge on the kit you want will pop up. I got to my config with suggestions to the gurus on here and ended up with the optimum config for my rig. Doesnt mean it will be same to yours.

Here you go, underseat manual! Print it all off and staple together. Handy.

https://www.manualslib.com/manual/1754548/Piaggio-Vespa-Cosa-Series.html?page=10#manual

Should be a BE5/140/83 and a 45 pilot according to piaggio manual.

Thanks SaFis, I will look into modifying that once I have it up and running and has passed it's test.

Thanks Ferriswolf, I'm temporarily in the Italian/Swiss alps so will need to make sure I do some tuning myself because the elevation here is probably quite a bit different to the setups which I'll get some insight from. It's nice to here your setup though. It's some bit of a starting point.

The PX's ugly sister but a great scoot none the less.

People weren't happy when the T5 mark 1 came out with the straighter rear end. The px are ten a penny and to see a cosa on road these days turns more heads imo. They are good scoots, the electromagnet auto choke on ignition and linked brakes seem a bit of a headache but I think scooterists weren't ready for the radical cosa change. People accept the GTS which sort of borrowed the recessed front guard / fairing of the cosa. Question of taste, I like them. As said before, they were never branded a Vespa on release, it was a piaggio cosa, meaning 'thing' . Trade poster shows piaggio on the horn cast, swapped to Vespa badge later on in uk to market behind the Vespa name. This is good link too for early cosa design drawings
https://scooternova.com/2014/01/19/the-vespa-cosa-how-they-got-there/

Of course beauty is in the eye of the beer holder but I reckon that the T5 is a big ugly too. I reckon as far as Vespa design goes, it peaked with the Rally and every subsequent scoot was a small step backwards in terms of good looks.

Agree, the Rally was not only beautiful on the eye but the 200 drove very well and felt far more stable than the px. I remember buying my first px and drove back from devils dyke in brighton , slightest bit of wind it would buffer across the road and thought there was something wrong with it, it had 800 miles on the clock and was pretty much brand new, like driving three wheeled shopping trolley . So less stable than the rally .

There's no doubt about it in my mind that the Cosa is the foxy step child of Vespa's. It is growing on my though And for the price I paid I can't complain.

Tonight I bought a crowbar, a hammer and an el cheapo socket set in lieu of a flywheel puller. First tap and the flywheel came loose. I had to leave it then so tomorrow I'll drain the gear oil and split the casing to see what delights are in inside. I'm used to having a workshop and lots of tools so progress is very slow while I'm here.

I guess age wise, its what, 35 years old? Hope it all goes well for you. Is the plastic floor covering missing in your photo?

Yes the floor covering along with the spare wheel and lots of other bits came in boxes with the bike. It also didn't come with a key so I had to order replacement barrels for it. I have changed the one on the seat and need to strip down the storage area to change the ignition barrel. It looks fairly complete in the photo but there is a small bit of work to do to it to make it usable again

I got the rest of the case removed this evening. Looks like the crank oil seal spring has broke loose and been injested by the rotary valve and a few other bits have wrapped around the crank.

I wonder if anyone could give their opinion on the rotary valve? the pad is fairly well scored like the crank. I've never run a 2 stroke with a rotary valve before so maybe it's some way useable? The last thing I want to do is put it back together though and then loose the cylinder.

Anyway it looks like it's a good excuse to go for a longer stroke crank.

More pictures please

I had my post typed out when I realised how poor the pictures were. Combination of bad light and greasy fingers on the camera lens. I will take some more this evening.

I have put in an order today for a new crank and other bits and pieces to get the bike finished. My last attempt at it finished in finding a castle nut on the crank which I didn't expect to be there so there is a castle nut tool on the order along with I hope everything else I will need to get it running with the new 60mm crank. Its all coming from Scooter Centre in Germany so I should have them in 2 days. I wonder have I forgotten anything. I'm hoping to get the old bearing out with a punch and a hammer so will see how that goes.

Does anybody know where I can find a spicy pipe for it? Once its up and running I want a proper expansion chamber for it.

Can we see a pic of the rotary pad in the case? The better the seal, the better they run - but they will run ANYWAY with some scoring and damage. If you don't like what you find, you can take a look here for some good options, including an easy one recommended by the factory: Welding and remachining rotary pad?

BTW, congrats on your Cosa, They really are a great bike!

Thanks V oodoo, hopefully I like it as I've never had a scooter before. My last bike was KTM EXC300 but it was never used on the road, it will obviously be a completely different experience!

I'm currently in Switzerland so I don't have any knowledge of somewhere that could work on the rotary pad for me and its damn expensive here so for now I'm going to just do the repair with chemical metal for now. i know of some reputable machine shops in Ireland so if there is an issue I will re-do the pad in Ireland.

This is the chemical metal I picked up, cost around CHF50 which was extortion but Wurth and Switzerland is a bad combination.

https://eshop.wurth.co.uk/Product-categories/Liquid-Metal-Fe1/31083006140201.cyid/3108.cgid/en/GB/GBP/

Its good for 120°C so there should be no issues with it.

I moved the bike to a friends garage because I was using the weather as an excuse to not work on it in the evenings. Once I have the crank removed with the new castle nut tool I will post a better picture of the rotary pad.

I received the castle nut tool for the clutch and it just keeps slipping. Looks like I'm going to have to drill out the nut on two sides and break it in two to remove the clutch and then the crank. This job has grown legs

Before you go hacking, can you provide a pic of what youre looking at?

My friend who owns the garage arrived with his toolbox from Ireland today so I finally got the nut out in two pieces. Took a small bit of time, I drilled two 6mm holes in opposing sides and then chased the nut out with a hammer and a punch. Not elegant but it worked. Excellent! I do have some more stripping to do though to make sure no swarf got into places where swarf shouldn't be.

The crank seal was in an awful condition, it seems to have melted the seal and the spring has definitely wrapped around the crank. I have all of the new gubbins to replace this stuff anyway. I haven't tipped the bike over the other way to see the damage on the rotary valve pad, I felt it with my fingernail though and if it had been paintwork it would definitely be the damage that needs a respray. Should have another update tomorrow.

I've also found that the stator wiring is quite old and all of the insulation is cracking and falling off. If I was at home I'd solder it but for the price of a soldering iron here I may look into a new stator and or performance flywheel.

A side note, the crankshaft nearly fell out when I tapped it with the hammer. A bit concerning. I haven't built a 2 stroke before but I don't think bearing clearances should be this loose for the crank. Anyway, new bearing and crank to be installed so once the case is good I should be fine.

Definitely shouldn't be able to tap a 200 crank out without some real effort! Need a pusher/puller tool so it draws in straight and doesn't take the crank out of true.

For the future, an old member Rob Hodge showed us a trick to grind down the sides of the clutch tool so it sits deeper and doesn't slip. Definitely worth doing to yours.

Stator rewire kits are available on the market for cheap. Just redo the solder joints and done. Cheap insurance so you're not chasing electrical issues down the line. Lightened flywheels are always good fun.

I would have ground out the socket but I have access to basically no tools here. I'm working abroad at the moment and when I started this project all I had was a 1/4" socket set. I don't particularly want to buy too many tools here because they are poor quality and very expensive and then I have the issue of bringing them home with me.

Better to change this castle nut to original one.
Or this DRT one.

1st gen Cosas had a 7 spring clutch so the later nuts will not fit…

I've bought a BGM anodised nut for it so that should sort any problems there.

So I got the scoot turned over on its side last night to inspect the rotary pad…. It doesn't look good.

The black bits in the scoring caused by the oil seal ring I thought were just oil, after some cleaning with brake cleaner the marks in some areas were not shifting.

I think it's part of the oil seal in the second picture which appears to have melted.

The third picture is the damage nearly all cleaned up. I used a small knife to get 99% of the rest of the rubber out of the grooves.

Finally I used the chemical metal to skim over the pad. It's not going to be perfect but until I find someone to build up the pad again I will settle for better. I will install the crank when I get back next week and check the clearance once I'm happy the material is smooth.

Great tip.
I mountedw on my mk.I 6 springs clutch that DRT nut. Is this means that it will fit to Cosa mk.I clutch?

Rotary pad on my P150X looking worse than yours. But it works good. Only problem that it sometimes won't start from first kick when engine is hot, need 3 to 6 kicks.

Got a little warm in there?

Yeah that seal is like a melted welly. I'm not even sure how that can happen….

I had let the chemical metal dry over the weekend. It had some high points so I put the end of the old crank in a drill and spun it for a while. This introduced a few of the small gouges back in but now it should have the proper clearance in general without any of the very deep gouges from before.

The new bearing tapped into place pretty easily.

The next job is to freeze the crank and heat the needle bearing race. I brought them home so the crank can spend 24hours freezing and I'll put the bearing in the oven. 200 degrees and it should fall into place easily.

That crank oil seal getting mangled and damaging the intake valve was a ton of bad luck.
Ive recently purchased a cosa 200 with 14000km and its more or less a minter. See oic on my query re side stand.
I had a PX 200 many moons ago and the handling was terrible....slight side wind and you're wobbling...likewise when a truck overtakes you. The Cosa, by comparison having been wind tunnel developed is a massive improvement as regards handling.Im still at a loss to understand why it was so unsuccessful.

Hi there! Sorry for offtop.

Maybe someone can help me with Cosa rear brake hose and gear cable routing?
My friend got Cosa in a boxes and now start to assembly it.
Can't understand how and where brake hose and gear cable must go when them came out from chassis. Is there must some bracket?

Pictures is very appreciated!
TIA

I had very similar damage on my rotary pad. I soda blasted it to get the gunk out of the grooves, followed by JB weld to level the grooves with the undamaged parts of the pad. I wrapped a feel gauge with 1000grit wet/dry to make it smooth. Even before I repaired it, the scoring on the pad didn't cause any issues, so you should be ok.