No power - Vespa Piaggio SI

Hi!

I have a 1980 Piaggio SI with literally no power. It starts very easy, it idles and it revs, but barely pulls itself forward. -let alone with me on it. Sounds good, but not very snappy when giving it throttle.

I have checked the following:

- It has spark.

- It has 125-130 PSI/8.5-9.0 bar compression.

- It has no decomp, hole welded shut.

- It has a overhauled rear gearbox with new bearings.

- It has .014" points gap, which results in points begin to open at about 20° BTDC.

- It has a newly overhauled engine, with new seals all around.

- No obvious leaks during leak-down test.

- It has fresh gas.

The moped have the following mods:

- Proma Circuit pipe

- SHA13.13 carb with a 62 jet

- Malossi air filter

- Malossi belt

Otherwise a stock variated SI.

My thoughts, which i hope to hear your two cents on:

The petcock is not new. I removed it when i painted the bike. I inspected it, cleaned it and could now see problems with it. When I have the fuel line off the carb it lets gas flow out, but only when turned to "reserve". The flow of fuel is good, but i dont know if its enough? Furthermore when replacing jets, the bowl has always been full of gas. Could the fuel-flow be too weak in any way?

If you have any other suggestions, I am more than happy to hear you out!

Thanks!(edited)

Re: No power - Vespa Piaggio SI

pretty

Re: No power - Vespa Piaggio SI

Richard Eberline /

Front or rear clutch is binding.

Re: No power - Vespa Piaggio SI

> Richard Eberline Wrote:

> -------------------------------------------------------

> Front or rear clutch is binding.

Could you explain this a little? The rear bell is just shaking when i give it gas with my feet on the ground, so I think you might be on to something. I filmed it as well:

Re: No power - Vespa Piaggio SI

brakes binding?

Re: No power - Vespa Piaggio SI

check your timing cam. my cam and woodruff key were ruined and I just flipped it around and have been blasting ever since.

Re: No power - Vespa Piaggio SI

My timing cam is brand new from Treats, though. Are they directional? Woodruff is fine.

Brakes not binding. Wheel is spinning very free.

Re: No power - Vespa Piaggio SI

It looks like there is some binding in the drive train. If you're on the stand and you give it a tiny bit of gas, your wheel should spin. In fact, it should spin a little bit at idle. Unless your wheel is touching the ground? I couldn't tell.

Jetting may be off. I've seen that setup with jetting as low as 58, and as high as 65. No power when running seems like a lean condition. I'd suggest you try up jetting just to see what you get.

Your electrical is fine, I think. Running reliably as it did with a good idle and no backfires, if it were me, I'd rule that out for now.

Re: No power - Vespa Piaggio SI

> Ike Pipe Wrote:

> -------------------------------------------------------

> It looks like there is some binding in the drive train. If you're on the

> stand and you give it a tiny bit of gas, your wheel should spin. In

> fact, it should spin a little bit at idle. Unless your wheel is touching

> the ground? I couldn't tell.

>

> Jetting may be off. I've seen that setup with jetting as low as 58, and

> as high as 65. No power when running seems like a lean condition. I'd

> suggest you try up jetting just to see what you get.

>

> Your electrical is fine, I think. Running reliably as it did with a good

> idle and no backfires, if it were me, I'd rule that out for now.

Yeah, I am holding the tire to the ground in the video. When on the stand with wheel in the air, it spins a bit at idle. Its when it must pull anything it just has nothing.

I can try to upjet, and report back. I have a full range of 60s.

Re: No power - Vespa Piaggio SI

Dirty30 Dillon /

Looks like your belt is not adjust correctly and the belt's spinning on the rear cheeks.

Re: No power - Vespa Piaggio SI

If the upjet doesn't work, I'd revisit the leak down. What method did you use?

Re: No power - Vespa Piaggio SI

i hear a clickity clickity sound, kinda like a sloppy piston or needle bearings in the rear pully or... take off the belt and feel for rubbing/smoothness.

Re: No power - Vespa Piaggio SI

> Dirty30 Dillon Wrote:

> -------------------------------------------------------

> Looks like your belt is not adjust correctly and the belt's spinning on

> the rear cheeks.

The rear cheeks are spinning, but the clutch housing i shaking like crazy.

> Ike Pipe Wrote:

> -------------------------------------------------------

> If the upjet doesn't work, I'd revisit the leak down. What method did

> you use?

Okay. I plugged up exhaust and intake. Then i screw in a custom air coupling that i’ve welded to correct thread to go in the spark plug hole. Then i hook up the air and have 4 bar on the dial. Then i go over hearing and using soapy water to check for leaks.

> pat splat Wrote:

> -------------------------------------------------------

> i hear a clickity clickity sound, kinda like a sloppy piston or needle

> bearings in the rear pully or... take off the belt and feel for

> rubbing/smoothness.

Yes, I hear it too. I have no idea where it comes from. There is a new piston and rings in it.

Does the pulley have bearings also? It feels smooth and easy when turning it by hand.

The belt gets wounded a bit, but cant feel any issues with either front- or rear variator smoothness

Re: No power - Vespa Piaggio SI

i guess u can run it without the belt on to hear if the noise is motor related. and yes there are two bearings in the rear pulley. not the clutch bell thats attached to the transmission but inside the moveable cheek rear pulley.

Re: No power - Vespa Piaggio SI

Your leak check seems legit. But if you don't find bubbles, at least watch the pressure gauge and see if it is holding pressure. If you pump it up and it drops pressure rapidly, you have a leak. It may be that the bubbles just aren't revealing it.

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