OP
UTC

Member
GTR / P125X
Joined: UTC
Posts: 16
Location: Switzerland
 
Member
GTR / P125X
Joined: UTC
Posts: 16
Location: Switzerland
UTC quote
Hello all,

I have a few questions on how to get my vespa running right. Background is that I have my first Vespa which I have rebuilt so not really sure what it should sound like. In any case I feel like something is not quite right.

Its a P125x from 1981 which I got with little history. It had a battery, but now it doesn't as someone sold me the wrong loom. It also has electronic ignition, so not points (not electric start).

When I got it it had a polini 177 kit on it, which I have removed. It also had the oil metering device deactivated with a bearing stuck in the tube. It also had a 116 main jet installed.

When I rebuilt I replaced everything that looked like it needed replacing such as seals and bearings. I got a used cylinder and head got a brand new piston also. Oil pump is activated and I have replaced the 116 main jet with a 96 (i read somewhere that should close to original.

Now. Please bear in mind I have little experience with these types of engines, or others practically speaking. I have been trying to tune the carb, but something is not quite right.

Engine was running and i could drive around, but the bike would vibrate like hell at higher revs and power seemed to be very poor I was struggling to get to 60kmph. I re-attached the exhaust and now its much much better, so its better sealed, now i can get to 60kmph in 3rd gear, which is loads better.

Now- the idling wonders all over the place. it goes ok for a bit then it wonders. I also hear a ticking sound when it is idling and a hissing. When I put the mixture screw all the way in it doesn't cut out, it just gets faster. after about 2 or 3 turns out it doesnt make any further difference to the ticking over.

Other information: I seem to remember that the squish was maybe 2.5 mm when i rebuilt it, it also had compression maybe 10-20 psi lower than numbers I saw recommended. I like at 350m, altitude and ride up to 1000 on some occasions, but 800 is something that happens often.

Carb jetting: Carb is delorto, 20/20 jetting now looks like its close to standard with starter, idle jet and now the main stack.

Timing: cant remember what it was now, but I measured very thing twice and followed the recommendations for a PX, not a p125x with points. BHS7 spark plug.

Looked inside the cylinder and it looked a bit wet in there. It does seem to start ok on the second kick now with the choke full out, but then when i ride off I have to put it back in as it stutters. I thought there might be an air leak so I drained the oil and put it in a jar, no separation doesn't particularly smell of petrol, maybe a very slight bit.

In terms of the timing, where can i understand what this should really be and if I have it right? could it being off make the ticking noise?

Also the inlet port on the case was made wider, I think it means earlier opening. Would this make a difference to what the timing should be?

Next im going to carry out the following:

1, Remove the carb and check its flat and sealed
2, leak down test on the engine
3, maybe slightly bigger jet for the main.
4, New mix screw for the carb
5, Take a mm off the head to get a better squish number

If anyone could guide me through some trouble shooting and a systematic way to get to a smooth running engine I would be very grateful. My Mrs doesn't want to come on the back to the ice cream shop right now so I need to get things fixed pronto before the end of the summer.

Many thanks for any tips
Chief
UTC

Veni, Vidi, Posti
Joined: UTC
Posts: 7091
Location: Tega Cay, SC
 
Veni, Vidi, Posti
Joined: UTC
Posts: 7091
Location: Tega Cay, SC
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I will start out by saying I'm not much of a tuner, but I'll try to help out anyway. It seems you have basically taken the scoot back to its original form. So my suggestions:
1. Definitely worth checking the carb for flatness. If you have not done anything to it than replace the jets, now is the time for a rebuild. Also, while you have it off, let us know what the jet stack is as well as the idle jet number
2. leak down - Yes, worth doing if possible
3. It looks like a 99 main is stock on a Px125e, but it would not hurt to have a few extras on the side
4. BGM makes a good one, just make sure it matches up with the one you already have.
5. This I don't know about, but others on here do.
On Timing: should be 18 degrees BTDC.
One question: You say it is a 20/20 carb - is it a Spaco or Del'Orto?
Also, I think the plug may be a bit cold as the B6HS is stock, but if you are doing long riding, the one you have may be best.
OP
UTC

Member
GTR / P125X
Joined: UTC
Posts: 16
Location: Switzerland
 
Member
GTR / P125X
Joined: UTC
Posts: 16
Location: Switzerland
UTC quote
Hi Tierney,
Thanks for coming back.

I just checked and we have the following:

Carb is a a Delorto- mixture screw thread is course.

Jets:
160/BE3/96
idle jet (i think its called) 40-120
Starter - 60

Many thanks
@scooterist avatar
UTC

Molto Verboso
71' Sprint Veloce , 05' Vespa PX150, 1978 P200E
Joined: UTC
Posts: 1558
Location: Tucson, AZ
 
Molto Verboso
@scooterist avatar
71' Sprint Veloce , 05' Vespa PX150, 1978 P200E
Joined: UTC
Posts: 1558
Location: Tucson, AZ
UTC quote
Are you testing the scooter at the same road and elevation ? or are you riding it up and down the hill. I suggest you find a baseline flat road to start the tuning. I have gone up to 3000 meters in elevation and absolutely all of my scooters becomes pic, including the GTS300 fuel injected. The elevation can make a dramatic impact on performance.

As far is finding the cylinder wet, be very carefull with your mixture screw on the back of the carburator. I had a problem with my mixture and it was a very elusive fault, it tunrs out it was the mixture too rich. It would run"ok" while hot but it will wet the spark plug as soon as you turn off the engine for a few minutes and it would not re-start. The fix was a simple 1/2 turn on the mixture and I never had an issue ever. The air mixture is dramatically sensitive and it can make the engine run terrible, to the point of not even start by fouling the spark plug.

what happened to the Polini? why did you want to leave it on? are you torquing the cylinder head? is the cylinder head flat with not warps?
OP
UTC

Member
GTR / P125X
Joined: UTC
Posts: 16
Location: Switzerland
 
Member
GTR / P125X
Joined: UTC
Posts: 16
Location: Switzerland
UTC quote
Hi Scooterist,

I took off the polini as I have only a license to drive a 125 and as the bike was off the road for so long I had to take it for inspection. So I didn't want any issues. I live in Switzerland and they can be very detail oriented with inspections.

We are torques up with no cylinder head leaks, its also flat. I'm testing at +/- 50 m altitude I would say. So I don't think its a factor with setting up, but maybe for a starting point?

Chief
OP
UTC

Member
GTR / P125X
Joined: UTC
Posts: 16
Location: Switzerland
 
Member
GTR / P125X
Joined: UTC
Posts: 16
Location: Switzerland
UTC quote
Morning all,

Here is video of the idling:

?si=zGT5Hfbb-7aurP9i

Any comments would be gratefully received. In this video you can really hear this ticking sound. Has anyone any adea what this could be?


Chief
@geeklion avatar
UTC

The Dude
Too Many piles of Junk that need too much work and too much money
Joined: UTC
Posts: 1738
Location: PNW from LBC
 
The Dude
@geeklion avatar
Too Many piles of Junk that need too much work and too much money
Joined: UTC
Posts: 1738
Location: PNW from LBC
UTC quote
sounds like the cruciform is catching on a gear. might need to shim out the selector box with an extra gasket.
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