2012 Piaggio Zip acts like there is a CPU restrictor. Confused I am!

Hi. I am familiar with 2 stroke tuning. My son has been riding 2 stroke MX bikes for 12 years and I do all his mechanical work. I am also familiar with 2 and 4 stroke road bikes and scooters as I have been building bikes for many years and also reconditioned 50cc scooters for an extra income.

But now I have an issue that I struggle with and here is hoping someone has the knowledge I am looking for.

I have a 2012 50cc Piaggio Zip that I have been tidying up. Motor was not running when I got the bike. Now it is running well apart from that when riding the motor will act like there is a CPU/CDI restrictor that hits after approx 45 k/h.

I have:
- Removed brass restrictor plate in carbi (scooter was struggling to go fast with the plate in)
- Removed spacer in variator
- Modified muffler by cutting away dead end part on muffler (and covered up the hole)
- Removed the feedback to the engine from the muffler (and covered the hole in muffler and the one to engine) Someone mentioned this was to a catalytic converter? Not sure.
- Fitted bigger main jet.
- Cleaned carbi and jets.
- Fitted new air filter.

After doing all this the engine became much more "peppy" and now has no hesitation when taking off. But acts like she runs out of fuel when I turn throttle past 2/3 of it's movement. (Speedo is not working, but I estimate the scooter is running at approx 40-45 k/h when this happens).

I also have an Aprilia 50cc 2 stroke scooter that has same CPU/CDI so i fitted that one thinking that there might be some restriction programmed in to the Piaggio CPU/CDI. But no change.

I have completed the work on this scooter (apart from fitting a new speedo cable) and it has turned out nice. But now I have this (above explained) last hurdle to overcome and need help.

 

Today I had a look at the muffler. No restrictor in input. But in the outlet there was 3 levels of pipes coming out (inside each others) at the output of the muffler. And as I am starting to run out of ideas I decided to attack them. So now only the outside one is left. I got a fraction more throttle movement and speed from that. But she also became a fraction noisier and the tone of the exhaust is more in line with a small 2 stroke MX bike...

I am reluctant to re-fit that restrictor brass plate in the carbi inlet. But will do a test with it in and see if I can get some more life in to the motor by changing main jets and as last resort drilling a hole or two additional in to the plate. The only thing I want is for the scooter to run well and a fraction faster than when it came out of the shop. Plus be able to use the whole range of the throttle and not, as now, just a fraction over 2/3's throttle.

 

Spent most of the day working on this thing. We are not friends!!
- Checked the reeds and they are fine. Tried to increase their movement by bending the back plates that restrict their movement. Tried smaller opening gap and as big as the motor allows. But nothing changed.
- I then tested all the main jets I have (53, 58. 60. 63). She runs best with the 63 fitted with or without the restriction plate in the carbi (the brass plate with the holes in it). I will now put a drill through the 53 jet. But the smallest drill I have is 0.8mm (that equates to a #80 jet). So as it is now 6.30pm I will tomorrow go and get drills so I can open up that 53 jet in intervals from 0.65mm to 1.00 mm... and if that does not solve the issue she will be sold as parts!
- But before I put her back in the shed for the night I will check that the vacuum fuel petcock works well. As would it not be ironic if my problem has always been that there is not enough fuel getting in to the carbi... in fact I will do that now before it gets dark and bypass that vacuum thingy!

 

Tested the vacuum thingy and I am glad that was not the issue!! How stoopid would I have felt! So tomorrow we will be drilling jets!

 

With a std exhaust and std airbox I would be fitting a 58-60 main jet here in the UK ! BUT start with a big jet then work down !

 

Thanks!

 

Thanks!

 

Have spent some time on the scooter today sorting the issue. I drilled the jet up in size until I got to 0.7mm. Now the motor happily keeps revving all the way, even if it looses the urgency to speed up fast at approx 3/4 of throttle. But on a flat straight it still slowly builds speed. And surprisingly it runs better with the restrictor plate in the carbi's intake! A small tweak to get that final 1/4 throttle to make a difference and we are done! Note that there is a Dellorto carbi on the scooter (just in case someone has a read of all this and their Piaggio Zip has another carbi as a result of being assembled in another country!)

 

So other things popped up and this project ended up on the shelf. Took it out yesterday intending to get the issue sorted. Tried all I could think of. Also fitted new speedo cable so I would know at what speeds stuff happens.
0 - 37k/h scooter pull strongly and quickly gets up to that speed.
37 - 45k/h scooter still keeps on increasing speed, but not at same urgency as before.
46 - 50k/h scooter slowly builds up to 50k/h and will not even on a straight go past 50k/h (I have not tried in a downhill).

I recon this would be the CDI checking the revs of the motor and once it gets to the revs that the scooter does at 50k/h it strangles it. This would mean that before I removed the spacer in the variator the scooter would never have reached 50k/h. (scooter did not run when I got it so I never tested with the spacer in).

The 70 jet is in carbi and the restrictor plate (that restricts the air intake) is in place. I have drilled one additional 5mm hole in it but that made no real difference. When I try to run the scooter without the restrictor plate it reaches 50 (by doing very much the same as when the plate is in the carbi), but I can only keep throttle at a fraction over half way, as if I turn the throttle more the motor dies. This would again indicate that the CDI is restricting the amount of revs.

Is the solution a new CDI that is not restricted?? Or is there something else I am missing here?

 

You need lighter rollers on variator Try 6gram.70 Main jet with brass plate removed.Then it Will hit about 70km/H.There is no restrictor om cdi not before 10 000rpm