Vespa SI won’t run right

Hi!

I’ve been having alot of issues with getting my Si to run right, and here is the list of what i have checked and done:

- Got rid of the Ebay engine case, and got a used OEM one.

- Checked all ignition components with multimeter, replaced condencer. Otherwise all good.

- New gaskets in engine, also using head gasket.

- New piston and rings.

- Set points to spec, and timed it. Checks out fine.

- Mini circuit lowboy exhaust because the old one was rusted out.

- SHA12.12 carb upjetted to 56.

After all this it started and idled fine. Four-stroked a bit, and had no low-end power what so ever. Had to run with it to get the engine to take over.

Then the banjo fell off due to destroyed threads, and the jet threads was also very bad.

This leads us to where we are now.

I had a SHA13.13 laying around from another vespa. Bought both a hi flow stock filter and a malossi air filter to go with it. Tried with the Malossi filer and the same 56 jet. It runs better, but still bad low end power. Will not idle when cold, only when warm. Also, the moped is a "fast" version, and now it does not hit 45km/h(28mp/h) as it do stock. Lights work as they should.

I am starting to get real tired of it, and would be forever grateful for some helping words from you guys.

Here is a pic of my newly restored Vespa, only thing left is to get her running.

Re: Vespa SI won’t run right

Richard Eberline /

Compression test PSI?

.016 point gap

plug NGK b5hs or b4h .019 gap

Re: Vespa SI won’t run right

note; once u get it running perfect .you'll want to run that plastic air shroud that sits on top of the cylinder, its important for cooling n it'll seize.

Re: Vespa SI won’t run right

> Richard Eberline Wrote:

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

> Compression test PSI?

>

> .016 point gap

>

> plug NGK b5hs or b4h .019 gap

It did 115-125 psi in the comp test.

Yep, points set to .016 or 0.40mm in my world

Got a NGK B5hs with .019 gap

> pat splat Wrote:

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

> note; once u get it running perfect .you'll want to run that plastic air

> shroud that sits on top of the cylinder, its important for cooling n

> it'll seize.

Noted! Will look into getting hold of one, as mine didn’t have one when i got it!

Thanks to both of you for answers!(edited)

Re: Vespa SI won’t run right

Anyone with any more tips or thoughts?

Re: Vespa SI won’t run right

bike looks good, u almost there, just cleaning carb n jetting w right filter should do it. ru running an inline filter? the small idle jet hole under carb slide gets clogged easy n makes idle fail. id get some more jets to play around with u can change em with carb on bike.

Re: Vespa SI won’t run right

> pat splat Wrote:

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

> bike looks good, u almost there, just cleaning carb n jetting w right

> filter should do it. ru running an inline filter? the small idle jet

> hole under carb slide gets clogged easy n makes idle fail. id get some

> more jets to play around with u can change em with carb on bike.

Thanks man! Not running a inlinw filter. Checked the carb, and gave it a good clean. No difference. But upjetted to a 63 from a 56, just to take a leap. It got better, and it will idle. But still surging from a stand still. Feels better if I dont go wide open from the start, but gradually increasing the throttle.

I tried a round with starter fluid. When i sprayed the bottom part of the crank case, it died. This was the only spot reacting to the spray. So i pulled the engine and put in a new crankcase gasket (covered it with oil) and a new crank axle seal. Torqued down to owners manual spec at 1.3kgm. Metal base gasket and no head gasket. While i had it apart i saw a little chip in the crank case, as someone pried the case open with a screwdriver or something. About half of the gasket surface it chipped away. Could this be enough to give me an air leak big enough to cause engine trouble?

It got a little better after the gaskets were replaced, but still no power off the line. Same surging and no go.

If this air leak could be giving me these problems, do anyone have a solution to fix it? It is temping to use RTV of some sort, but I really do not know if it would do any good..

Hope you can help, and all answers are highly appreciated!

Re: Vespa SI won’t run right

dont use rtv, i always smear motoseal1 on both sides of the case gasket. and yes any air leak is gonna mess with your performance

Re: Vespa SI won’t run right

Some pics of carnage would have been nice.

Re: Vespa SI won’t run right

> pat splat Wrote:

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

> dont use rtv, i always smear motoseal1 on both sides of the case gasket.

> and yes any air leak is gonna mess with your performance

Ok, so you use motoseal with the gasket. Always thought it was one or the other. Is it any danger of getting motoseal in to the engine, it i squeezes out a bit on the inside? I can get my hands on Permatex gasket sealer. Check the link:

https://www.permatex.com/products/gasketing/gasket-sealants/permatex-aviation-form-a-gasket-no-3-sealant-liquid/

Will this do the trick, or do i need motoseal1?

As the engine is installed back in the moped, i dont have a picture. But i drew the chip-size on the old case with a permanent marker to show you the size:

0CCD3EA5-DC0A-4515-8E46-DEA3D3CFBCD5.jpeg

Re: Vespa SI won’t run right

Bad Cadillac™ /

Put the original carb/jet back on and exhaust if it's not rusted out beyond use since those are the only two performance mods you've done to it. You can't tune it or do upgrades until you get it to run correctly.

If you take the carb and pipe out of the mix and it runs right, then you know the issue is from one or both of those parts.

If you take it back to all stock and it sill does not run right, then its an issue with something else you messed with.

Here's my restored Si:

66762263_708329069604124_62686525153869824_n.jpg

Re: Vespa SI won’t run right

> Bad Cadillac™ Wrote:

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

> Put the original carb/jet back on and exhaust if it's not rusted out

> beyond use since those are the only two performance mods you've done to

> it. You can't tune it or do upgrades until you get it to run correctly.

>

> If you take the carb and pipe out of the mix and it runs right, then you

> know the issue is from one or both of those parts.

>

> If you take it back to all stock and it sill does not run right, then

> its an issue with something else you messed with.

>

> Here's my restored Si:

Thats the problem. I bought the moped in parts, with many parts rusted out or destroyed in other ways. Therefore no stock exhaust and a stock carb that leaks like hell.

I sort of have to figure it out with the lowboy exhaust and 13.13 carb.. -and i cant believe that neither of them are to blame.

But as I have "messed" with every nut and bolt, i am sure the problem is with something i’ve messed with.

I’ll try to fix this air leak in the crank case first, and then see whats what. Stock or not, that air leak is cooking up trouble. When the engine no longer reacts to the carb spray, we’ll see how she runs.

That is a super clean looking SI, man. Love the work. The Puch is also a looker!

Re: Vespa SI won’t run right

Bad Cadillac™ /

Humm, ok I see now.

I see you've also looked for air leaks. Your stock pipe is completely useless? I mean you can't even connect it at all?

Are you using the stock variator?

You said it wont idle when cold. When this happens, what happens when you use the choke on it and it's cold? Does it idle then?

And thanks, my Si rips! My set up is similar to yours, 13.13 carb and hi flow filter, giannelli pipe, olympia variator, malossi belt and stiffer rear clutch springs.(edited)

Re: Vespa SI won’t run right

Bad Cadillac™ /

Do you have any higher number jets?

Unfortunately I don't remember what jet I'm using but pretty sure it's the one that came with the malossi 13.13 or slightly lower.

Re: Vespa SI won’t run right

Bad Cadillac™ /

Vid of my Si running:

Re: Vespa SI won’t run right

> Bad Cadillac™ Wrote:

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

> Humm, ok I see now.

>

> I see you've also looked for air leaks. Your stock pipe is completely

> useless? I mean you can't even connect it at all?

>

> Are you using the stock variator?

>

> You said it wont idle when cold. When this happens, what happens when

> you use the choke on it and it's cold? Does it idle then?

>

> And thanks, my Si rips! My set up is similar to yours, 13.13 carb and hi

> flow filter, giannelli pipe, olympia variator, malossi belt and stiffer

> rear clutch springs.

No, i don’t even have it. The mounting brackets were bolted to the frame, full of rust, and no exhaust to be seen.

Yes. Stock variators front and rear.

Yea, or i comes and goes a little. With the 63 jet it idles most times. Other times i have to give it gas and a few revs, and then it idles. With choke it dies out.

After i replaced the crank case gasket hoping it would stop the air leak, it ran a little better. But the air leak was still present at same spot. So i have dropped the engine again and taken it apart. The piston was covered in black soot on top, and the plug was blacked out as well. Doesn’t this mean it is running a bit rich?

Ah, thats a sweet setup. Hope to get something like it one day!

Re: Vespa SI won’t run right

A little update with a video. Some info on the video. When riding it i tried to accelerate as fast as it could, both with full open throttle and gradually opening it. See for youself, and let me know what you make of it:

Re: Vespa SI won’t run right

Bad Cadillac™ /

Such a great looking bike you got for sure!

OK, it dies with choke, that's normal and good.

Yes, black plug means rich and is loading up.

It does seem to idle well and bring itself back to idle after riding.

Do you have lower jets to try?

It really seems like a jet issue to me because it bogs on you when you try and take off and then comes to life as RPMs get higher. At first I thought you might need higher but now that I see, hear it and your plug was black, I think lower now.

Definitely fix the air leak too of course.

Re: Vespa SI won’t run right

The motor no longer reacts to the starter fluid, so i guess it is sealed and all is well in that department.

Setup in video:

- 13.13 carb with 58 jet (63 in first clip only)

- Malossi hi flow air filter

- Proma circuit low boy exhaust

- B5HS spark plug

- Malossi belt

Otherwise stock engine and drivetrain

Re: Vespa SI won’t run right

Have now tried to jet down a bit. Tried a 56 first, then a 54. Pretty much runs the same.

But here is a video of the drivetrain under load. Holding the back wheel down while it’s on the stand and giving it full throttle. Is it normal that it is this dull?

And it also chews belts. This a Malossi belt i bought last week. Moped have only been tested and maybe gone 1km with it. See picture below.

58593D7D-6ADC-4608-BBC5-8F91E59637D7.jpeg

Re: Vespa SI won’t run right

Could i ask what those forks are. I think i saw them on treatland. It says they fit caio. Looks like they fit nicely on the si.

Re: Vespa SI won’t run right

I only see the belt cords fraying part of the way around that belt. That would incline me to break out some calipers and take several width measurements for comparison. I bet the belt is wider at the "chewed" locations. If so jbot has a fix for that.

Read!(edited)

Re: Vespa SI won’t run right

> Kristian Lomeland Wrote:

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

> So i have dropped the engine again and taken it apart. The piston

> was covered in black soot on top, and the plug was blacked out as well.

> Doesn’t this mean it is running a bit rich?

It can. Pics would be nice.

Too cold of a spark plug will prohibit the combustion chamber from getting hot enough to burn cleanly. I see several references to plug being used but what is it supposed to have? Whats the spark look like?? Again pictures please. You may have a failing ignition coil causing all of this.

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