Trying to squeeze the last bit of this PX out
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Member
PX150E
Joined: 23 Dec 2018
Posts: 17
Location: Vietnam
Fri Feb 22, 2019 5:55 am quote
Hello world !

My bike currents setup : pinasco 177 with pinasco crank, si 24/24 autolube carb with polini venturi, 23 teeth cog, stock ignition, pilot 62/160 - main 120-160-BE3, NGK B6ES Spark plug

Testing it on WOT, at third gear it would scream it way to 90kmh. Shift to fourth, it would goes to 100kmh and then it would feel like it losing power at half throttle. I give it more throttle but it would bogg down even more, the rpm could not go past 3500rpm. Scared of seizing the motor, I backed out and come up here, asking for some knowledge.

So, what could I do to fix this. This same bike with this setup used to max out at 130kmh with a leaked fuel tap on the same stretch of road.

Low RPM smooth as silk and idle beautiful. Third gear WOT feel great. Just the last bit of the fourth gear

Here is a picture of the spark plug after the pull and just a picture of the bike



Ossessionato
05 Stella, '62 VBB, 76 Sprint V, 63 GL
Joined: 16 Jun 2011
Posts: 2256
Location: Chicago. Well, Evanston, but that's almost Chicago
Fri Feb 22, 2019 6:14 am quote
Nice looking scoot I wish any of mine looked half that nice, but all I ever seem to build are shifty rat's.

Basically, you're over-geared. You need to either drop back to probably a 21t clutch or else install a short 4th.

To get to 90 KPH in 3rd, on a PX with stock gearing and a 23t clutch, that means your WOT RPM's must be about 7,200.

Your power output needs to be around 8.5 HP (it does for me at least, but I weigh a little over 200 lbs).

So if you look at your power curve, it almost certainly isn't going to be making anywhere near 8HP at 3,500 RPM's. You probably need to be up closer 5,000 for that.

By reducing your gearing, you move the shift point to 4th up where you have enough power to overcome air resistance.

If you can generate some dyno curves with the GSF Dyno App (free from the German Scooter Forum guys), then that will tell you what you need to get to, gearing-wise. I also have a spreadsheet I've built that can do it a little more formally.

Mostly, though, at this point, we need more data to say for sure.
Member
PX150E
Joined: 23 Dec 2018
Posts: 17
Location: Vietnam
Fri Feb 22, 2019 6:23 am quote
thanks chandlerman, we do have some great painter in my part of town

I actually put the bike on the dyno recently, and here is the dyno sheet. I hope that you could clarify something for me. The bike make 11.5hp to the wheel.




AT the time when the bike was on the dyno, I have to use the stock 57mm cylinder head because somehow SIP shipped me the piston kit without the head. But now I got the right head on and it feels like it have a 2-3 more hp, I barely have to twist it around town now.
Member
PX150E
Joined: 23 Dec 2018
Posts: 17
Location: Vietnam
Sat Feb 23, 2019 5:29 am quote
Found the problem - here is the update, somebody might need this in the future

- One of the cylinder stud failed which led to a cylinder head leak. Which decreased the performance of the motor.

- The leak also caused tiny scruffs on the cylinder wall, because the piston was probably overheated because the leaked head lean out the air fuel mixture in the combustion chamber. Luckily it did not seize.

- I changed the broken stud and it pulls it way to 120kmh again , but I would probably keep this bike mainly for street use now
Ossessionato
05 Stella, '62 VBB, 76 Sprint V, 63 GL
Joined: 16 Jun 2011
Posts: 2256
Location: Chicago. Well, Evanston, but that's almost Chicago
Sat Feb 23, 2019 5:46 am quote
That's good to hear, but I'm curious if that speed was off a Vespa speedo, a magnetic sensor speedo, or a GPS?
Hooked
50 N
Joined: 20 Dec 2015
Posts: 267
Location: North Aberdeenshire
Sat Feb 23, 2019 3:50 pm quote
B6 is the wrong plug for a start, bare minimum you should be on a 7 or even better an 8.

What 23 tooth clutch drive are you using? If Piaggio your gearbox really won't like it and it will shit it's pants sooner or later.
Member
PX150E
Joined: 23 Dec 2018
Posts: 17
Location: Vietnam
Sun Feb 24, 2019 5:24 am quote
@chandler, It was GPS speed, the tach was 7-10kmh faster at 100kmh I think.

@Juan, Iím using the BGM clutch which also reduce noise. The piaggio 23 tooth cog from the sprint I believe wonít fit in the px. It was 2mm wider in diameter.

I overnighted brand new set of studs from DRT and it could cruise at 110kmh now (gps)
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