Modern Vespa

Hi everyone, my name is Robbin and I just subscribed to this forum. I have read your comments in the shadows for a while and would like to ask you for your opinions.

Last december I bought a Vespa PX200E from 1984 to restore it. In the meantime I rebuild the engine, replaced al worn parts, new standard exhaust, and lots more. Unfortunately I can not get the PX200E to run it properly.

The idle is perfect no problems there, I can easily drive away in the first gear, when I shift to the second gear there is a slight dip when trying to drive in second gear. When I fully open the throttle it pulls great. This problem becomes worse in a higher gear and in 4th gear the scoot somethomes almost dies. So it is only while riding and becomes worse in the higher gears. Full throttle runs good and idling also runs fine. This happens just when I start opening the throttle in the next gear.

So idle is no problem, full throttle is also no problem. What can this be?
What I have done already:
- Cleaned the carb in ultrasonic bath
- Cleaned the jets with carb cleaner and pressured air
- Cleaned air filter
- Checked timing, it is perfectly on 23°
- New fuel hose and no air bubbles
- New fuel tap (Fastflow)
- New spark plug/spark plug wiring/spark plug cap

None of these resulted in the solution and now I don't know where to look anymore. Any suggestion is welcome!

Cheers!

What about your mixture screw adjustment?
Have a look here for lots of advice: Mixture screw adjustment, got a good link? .

And what jets are you running?

The mixture screw was pretty okay 1,5 turns out. Did not really fiddle with that because idle was running perfect.

Idle jet is 160/55
Stack is: 160 AC / BE3 mixer / 118 main jet.

Could this simply be only a mixture screw setting?

Mixture screw only affects the idle, but that's not its main job. Read the thread and have a go at it, see if it improves things for you. I'll let others comment further on your jetting and you can check this thread: Guide: SI Jetting Chart + How to Tune an SI Carb , which includes this stock jetting chart suggesting your main jet may be slightly big.

Also welcome and good on you for getting this far! ... but we NEED pics of your bike to give you our best efforts!

Maybe you are just shifting too early? They want to rev and don't like short shifting.

Smaller motors need to rev more maybe, but a 200 should have lots of grunt down low. How big are you Robbin? I'm over 200 lbs & I rarely rev my P200, I putt around in 3rd & 4th.

I have been told that the 118 was standard on this scoot but your chart clearly shows otherwise. I will have a go at it thanks for the advice! First I have a week away so I can not try this directly.

I am 220 pounds so quit big i suppose. What speeds are you roughly shifting? I am used to torque motorcycles so maybe I am shifting to early. Never really thought about that

I'm not gonna tell you until you comply!

The jet chart isnt necessarily accurate for European scooters, for example showing 100 main on px125, in UK they are all appear to be 96 standard, ive had four over the years and all 96. So thats 4 pts over which on a standard scoot would be rich. We have had various Euro emission rules too meaning setups are borderline lean. Its ok as a bullpark i guess but I wouldnt rely on it as gospel if you have a european scoot. Sure use the chart to get in the bullpark then test, plug chop whatever floats your boat.

Voodoo I am not at home right now, but this is a pic of my scoot where I am almost done! Will take a better picture when I am back. Your help is much appreciated!

OK, dues paid up for now. I must say that I love me a clean white P and a late model 200 w/ disk brake and column ignition/lock is so hard to find in any condition. Yours is a gem, and I'm looking forward to more!

My '78 P200 is in remarkably good shape w/ just over 10,000 km which I recently turned over myself. I got it not running from an older guy who gave up riding and who kept it stored under cover. He drives his car most carefully, so I imagine he did the same w/ his Vespa. It is totally stock, runs great and always starts first or second kick after I did a bit of carburetor work and now is my main ride. You can see it here, it eats those hills with no drama at all, throttle does just what I ask: https://modernvespa.com/forum/post2613748#2613748

But most of my riding under load is on a slight incline or level. If not in traffic I usually will give maybe a quarter throttle until I hit maybe 25% max RPMs then shift. I go around 90 degree corners if no stop sign slowly in 3rd gear sometimes feathering the clutch. I dump it into 4th once I get up a bit of speed w/ quarter throttle in 3rd. Sorry I can't guess how many RPMs, but not a lot like my hotrod smallies need.

In traffic I make sure I keep up with the cars which is easy and usually filter to the front at traffic lights w/ most of the other 2 wheelers. There I charge off on green at full throttle, lots of RPMs and am annoyed when I get beat up to the speed limit by a big motorcycle, or worse, a bigger SCOOTER .

Your 200 tuned right ought do be able to do same or better, even if you like to accelerate faster.

They shipped 118 premix/116 autolube from the factory on Euro spec bikes.
Original (Dellorto) carb?

Yes its a premix and with an original dellorto carb.

It has no front disc brake though just a drum

I will try and fiddle with the mix screw but in the meantime I am curious if there are other ideas. I heard from someone else that it could be due to a worn carb?

How old is the exhaust on it? Has it been decoked? You will get compression but shitty running if exhaust is past it's best. Just one thing to maybe consider .

Exhaust is a new one

Back in 2018 I paid someone to do a two engine swap. When I got the scooters one of them would run good on first and second but they would die(hesitate) in 3rd and 4th at ful throttle. it took me a while to figure out but I found it on my own.

The problem was that the "mechanic" swapped the fuel line and put a thick black generic flue line from auto zone but the line was so thick that it was being pinched against the chasi by the fuel tank. I replaced the lines , rerouted the fuel line and it solved the problem.

Although my history is more freak than anything I don't think you would have the same issue. I am more incline to say that your carburator set-up is the culprit. Specifically I am guessing either the mixture adjustment on the back of the carburator or a combination of atomizer/main jet.

Make sure that the connectors on the coil and the CDI are properly tight as this causes a lot of misfiring. Also, be aware that fuel valve can also be faulty.

Lastly, ensure that the carburator is properly seated/torque. Everything that I mentioned I ran into problem with.

Never heard of a worn carb

If you want to fiddle with the mixture screw, get it warmed up, turn the screw 1/4 in either direction and see how it feels.

I suspect sdjohn is right, though. Upshifting too low in the power band will mimic a jetting issue (bog).
4th gear is also very tall from 3rd into a headwind.

Play with it by increasing rpm's and feathering the clutch to accelerate, like Voodoo does
If nothing else, it will provide more clues.

Basically thrash through each gear till it revs out to get anywhere. That's how I've driven all my scoots for 40 years plus. 1st and 2nd are useless unless it's steep inclines, get into 3rd as soon as possible and wind right up to full Revs before changing up. If you're running a polini box or road 2 all the power kicks in on the upper end of 3rd.

I do not seem to get the adjustments right. Is there an easy way to check for airleaks? I really hope to rule that out.

At what speeds are you roughly shifting?

With the engine cold - see if you can move the carb by hand. Even if you can't move it a bit, the carb bolts may need to be retorqued. Also check the torque on the cylinder head bolts as well.

One more thing - you do have the 24/24 carb, right? If so, that stock jet profile you have is right. I only ask because some of the P200s sold in the states came with a 20/20 carb.

Thanks for the tips! I have the 24/24 carb indeed.

Will try the carb wiggle for sure, but I bolted the carb and the cylinder head with a torque wrench so should be allright.

For air leaks I use the ol' spray-carb-cleaner-in-spots and listen for obvious idle changes.

I'm dealing with a similar (or the same) problem...lots of what I call chugging in fourth, sometimes in third on high revs. I upjuetted when I installed a new SIP 3.0 exhaust, thinking of going back to stock jetting to see if it makes a difference.

Long-shot:
Do you know if the plastic tray under the fuel tank is installed?
Sometimes that can get removed in its history. Not having it there into a headwind or at speed will have results somewhat similar to what you describe.

If you're unsure, tape over the grill on the horncast to see if it makes any difference.

Thanks for the tip Ray! I heard that one before so i just installed the piece of plastic last week. Went on and played around with the main and idle jets.
Got it running okay and with the tip of shifting to early in my head I went on a test ride. What do you think? It went great!

So I put on my bad boy shoes and went for a longer ride. 6 km away from home the scoot dies. Had some tools with me because I did think something would happen. But first took the opportunity to make a picture.


After a while I found that there was no spark anymore. Never had this but I replaced the spark plugs the cap and wire but I ended up walking home.

The spark plug color was like the picture below. Now I have to find the culprit of this problem...

I don't know if someone is still reading this, but I will give an update anyway .

I did the following things to check why I don't have a spark:
- Check for a spark without the green wire attached to the CDI
- Try a new CDI
- Measured the resistance of my stator (all was good)
- Tried a new plug/plug cap/plug cable

After all that I still did not get any spark, but yesterday I assembled everything again and what do you know, a spark!

Now I am fearing that there is something wrong somewere and it can pop up at any moment, but lets see.

I tried running the scoot again and noticed that when I run it in idle it runs fine, it revs fine too. When I want to leave in first gear it almost dies with the throttle opened a bit. I have to fully open the throttle to drive off. When driving in second gear and let go of the throttle, the vespa almost dies.

The dying when driving away gave me the idea that the adjustment screw is to rich, but dying after letting go of the throttle gave me the idea that it is too lean. Do you guys have any tips for me?

Check the gearbox oil is ok. No power unless full throttle is symptom of an air leak.

Otherwise. Broken stator wire. Pull the spade connector to check any wire isn't internally broken.

Pilot jet blocked?

Do a crankcase pressure test.

Thanks for the suggestions Jack!
The stator is fully checked and seemed ok.

The gearbox oil and pressure test are the next on my list. Those have not been checked yet!

So I checked the oil, no gas in there.
I also did a pressure test and I am losing some air right where the cilinder is meeting the cases. (About 1 hhmg per second)
Attached a video of the losing air and the place (I can not seem to upload it). I also attached a photo of my pickup. To the more experienced eyes how does this look?

I already tried to tighten the nuts a little more to help close the air leak but no luck. Is this bad enough to split the cases again?

I am going from 160 hhgm to 110 on one minute. Attached the spot of the air leak.

Is it where the cylinder head meets the engine cases?

If so, I would first try checking the torque of the head nuts and tighten a tiny bit more.

If that didn't work I would pull the cylinder, add little bit of a gasket sealer, and try again. Most recently I used spray copper gasket sealer on a new gasket and it went just fine.

Good luck.

Yeah I am already at 20 Nm. I don't know what you use? Is it lb-ft? That is around 14. Don't know how hard I can torque them down but a tiny bit extra did not solve it.

I will look at the gasket sealer! Really hoping to not split the cases again

No more!
You can easily strip the threads in the cases with any more than that.

Remove the cylinder in-frame (double-nut the bolts to remove them, and inspect/clean the threads).

Apply Dirko HT in the following manner:

So I just applied the Dirko to the air leak spot. It was a logical fail, the gasket of the two cases was just pushing against the gasket of the cylinder. Cut a bit of gasket away and applied the Dirko so now waiting for it to set and measure for air leaks again.

In the meantime I wanted to install a new pickup because of the lost spark without a clear reason the other day. Attached a picture of the old one and the new one. Needless to say that this one is going straight back.