Modern Vespa

Done while riding.

👍

Thinking about splitting the cases myself. I have the time. I want to avoid removing the engine completely though. How much can I accomplish with the engine still in the scoot? Can I solve my air leaks?

I'm on the list to get it into scooterwest, but who knows when that'll be.

You can leak test it on the bike. Just need to remove the carb and drop the exhaust.
Search here using "leak test," as there are a few ways to do it (and not much $).

Have you strobed it?

I strobed it when I initially timed it and everything was fine I believe it was right around 18 or 19 degrees btdc. If i remember correctly turning the stator in 1 direction all the way gave me the needed degrees.


UPDATE: Engines out. Cases split. Im diving in. Pretty easy so far. Going to ensure things are done right.

If only those marks on the bore then not bad but still shouldn't be there.

Confirm what jetting is in there now, AC140 BE5 115 52/140?

The idle instability is a sign of an air leak with a 52/140 pilot jet.

Yup, that was the jetting.

Have you remove the fuel tank lately? I had similar symtons and it was the fuel line that was the worng size(to fat) and was getting softly pinched against the frame. The scooter ran great in first and second because the shifts happened too fast but the moment to shifted to third and fourth you had fuel starvation.

I also had a similar issue and the problem was the fuel tab. Initially it was sort of random but it got bad and the fuel valve couldn't supply enough.

Other than that I had many other fuel starvations over many set-ups but that was when I switched cylinder kits, exhaust etc and was on the road trying to dial in (trial and error). Good luck to you.

I did just have the fuel tank out last night to replace the rear shock. Fuel line was okay. This kind of just happened all the sudden, and I couldn't get it under control. The engine is back in the frame after a rebuild to my best ability, and I'm actually doing the timing right now.

Are you running a resistor type spark plug and resistor type spark plug cap? If so, this can cause ignition issues with points ignitions too! See my 1980 P125X Resto Mod thread for more details regarding this.

Hec

P125x
Malossi 177 cast iron
Mazuchelli 60mm race crank w/spacer
Case ported as best I could
All new bearings/seals/gaskets
20/20 carb 120/BE4/115




I just got the engine buttoned back up after the rebuild. Had some backfiring and running issues, so I checked the case bolts, and they absolutely needed to be retightened. That cleared up the backfiring issue, so I rejetted, and retimed (turned stator all the way anti-clockwise).

Theres an intermittent metallic tapping sound that comes and goes from the cylinder. Not sure what could be hitting. I'm using a paper base gasket, spacer plate, and rubber cylinder head o-ring. Absolutely no marks on the piston. Just checked with my camera.

ALSO, I just Googled what pinging sounds like while cruising on an older scoot, and I absolutely heard this before the rebuild. I thought it was a noisy speedo gear.
https://m.youtube.com/watch?v=3wQJ4oo_Jgk

Suggest have another check of that again perhaps. All way anti-clockwise is running full advance! I've never had to put a stator in that position on the slots, not even the variable timing ones.

This could be the reason for your metallic noise (pinking).

Couple things. I just checked the squish with some solder, and it came out to 1.34. when I checked the malossi instructions, it says to set it at 0.7, so my squish has been off since the day I put the kit on. As for timing, I'm going to set the stator to the middle position, and just set the 18° btdc via a degree disk.

Sorry if I'm telling you something you already know, but you have to be 100% sure your timing is right. Otherwise, you're just running in circles.

And the only way to be sure your of timing is with a strobe.

1. Find TDC
2. Make marks with a white marker on both the case and the flywheel
3. Make another mark on the CASE ONLY 18° counterclockwise from the first mark. Write "18°" next to it.

When you run a strobe light, the mark on the flywheel should line up with the 18° mark on the case.

If it doesn't, pull the flywheel off and turn the stator. Clockwise retards timing (makes the points open later), counterclockwise advances timing (make the points open sooner).

Tried to strobe it lastnight, but the light took a dump. I'll pick up another strobe today.

FWIW,

Jack advised me to set the timing on my 177 build with the following:
"With points the timing should be set to 22, on electronic 18."

I originally had mine set to 18 degrees and took Jack's advice and they are now set to 22 degrees as I have points.

Hec

I'm not sure what I mixed up during the timing process, but fully retarding the stator puts the timing at 18° btdc, strobed. My capless spark plug was also arcing against the choke cable housing.

As far as squish, I've been hearing things from 0.7, to 2 mm. Molossi says 0.7 or 0.8, I think. My squish was at 1.3 if I used a paper gasket along with the spacer for the longer crank. I removed the paper gasket and used some permatex and my squish went down to 0.8.

There is a metal on metal clinking sound with every stroke of the piston, but absolutely 0 marks on it.

If you remove the plug and spin the engine over, using your hand on the flywheel, do you hear the metal on metal sound? If you don't then it's gotta be detonation due to timing. Make sure your points are gapped correctly too. On a wild ass guess, could something be rattling around inside your exhaust? Can post a video of the engine running?

Hec

I agree that it must be timing related / detonation. Somehow during my timing process, I set it so advanced, that retarding the stator completely, brought the timing to 18° btdc. I'm not sure what I'm doing wrong. I'm following this method:https://modernvespa.com/forum/topic177892


Just timed/strobed it. Stator in middle position. Points are at 0.45mm at TDC. Still strobed around 10btdc, and the detonation remains. Also the idle was uncontrolable. Lol. I'm about done with this thing.

This a great video on setting the timing with points ignition. I used it when I set mine. If your points gap is open too much the timing will be advanced. If the points gap is too small the timing will be retarded.

?si=LUEX-0ERU6BKBJVv

Good luck

Hec

Decided to finally build a pressure tester. Blood pressure cuff, t-fitting, expanding plug, and a 3d printed block-off plate.

At least that'll confirm a leak, before i tear this thing back down.

Update: Cant for the life of me get this thing to hold any pressure.

UPDATE:

Had the stator reworked, and got it timed today @ 18°BTDC. Stator is once again full advanced to get there.

Other than what I'm told is piston slap, since the piston doesn't appear to be hitting anything, it started right up, and ran fine. Waiting for it to cool down now to retorque everything.

FWIW the VMC Super G kit I ran for about 3000 miles had some pretty gnarly piston slap sound but it just ate all the abuse I threw at it. Never had any issues. Some kits are just a bit rattly from what I've seen.

Make sure your leakdown tester fully seals what it should seal, then start squirting soapy water around all the possible leak places. Case half seam, cylinder base, cylinder head, and main seals. If you cant find anything there, it is likely the gasket surface that seals the crankcase from the gearbox; there is a very thin spot there. If there is a major leak there your engine will suck gearbox oil.

Sorry to ask this again, but I just discovered that I actually have a 24.24 carb on the bike, not a 20. 20, like I thought.

Recommended jetting?


Currently:

P125x
Malossi 177 cast iron
Mazuchelli 60mm race crank w/spacer
Case ported as best I could
All new bearings/seals/gaskets
Road2 exhaust
24.24 carb
52/140 idle
120/BE4/118

I ride mostly around town(under 25mph), and the throttle is barely cracked open, and VERY spluttery. Like, obnoxiously so.

Took it up to 60mph this morning, and temps didn't get above 250. Felt good. Though if I let off full throttle, it increases the speed almost instantly

Man by what you're describing when you let off the throttle, it sounds like you're too lean. If it won't idle it's too lean. Next time apply some choke when you're riding. If it idles better then you know it's lean.

Hec

Hec

Sorry, I meant to clarify my post, but you got to it faster than I did. What I meant was, at full throttle I was holding steady at 60 MPH, if I let off to around 3/4 throttle, I sped up to around 65 mph. It idles fine.

I've heard of this happening before, but I can't remember if it was one of those situations where what I think the problem is, is actually the opposite. Like, I would think that maybe my 118 MJ is too lean, so at wot, it's not enough. Or maybe it's too rich, and bogging down the engine.

Ok

First let me start by saying I am a rank amateur and have never jetted a Vespa. Im going through this exercise myself for the first time. So take this info with a grain a salt.

You may have already read this. But incase you haven't here it is.

From NSM Wiki page on tuning SI Carbs

Wiki [D] Guide: SI Jetting Chart + How to Tune an SI Carb.

6.3) Tuning the atomizer is the same basic process as the main jet. Start rich, work your way down. If you have a 177 top end, start with a BE4. The Malossi 166 kit used to ship (maybe still does) with a BE4 and (I think) 125 Main Jet. No AC, though. Go figure.

If the BE4 is too lean, then you need to drop your Air Corrector (So 160 to 140; 140 to 120; etc.) and start the process over with the main jet, as it should now be too rich.

Once you're on the correct AC, test riding in 3rd gear by getting to the low end of the power curve, then dropping back to half throttle. It should continue to accelerate, albeit not as quickly, but also not stumble while it gets to a cruising speed.

Your description fits above and therefore I think your AC and atomizer combo is close. I would try bigger main jets and work your way down. What's the biggest MJ you have to try?

Others please chime in.

Hec

Late to the party here but all of this points to an air leak for me. I really believe you are chasing ghosts until eliminate air leaks from the equation.

I think the air leaks are taken care of. It's running pretty well at the moment. Just getting the jetting correct now.

Did you leak down test it to be sure?

Leak down test with oil in the intake inlet? Or a pressure test?

Pressure test.