Modern Vespa

Hi! Brand new to the forum.

I've been riding an LX50 2V for some time now, it has the Malossi 78cc kit with the camshaft, a Turbo Kit GMax pipe w/ header wrap, upjetted to 82 main, Malossi Double Sponge air filter, adjustable Bitubo front & rear shocks. I've been enthusiastic about this scooter and I use it a lot. I prefer it to the car weather permitting.

However I've been having trouble with bogging from a stop. The engine idles fine, just when I twist the throttle to move off from having sat at a traffic light for a few moments it bogs so I have to feather it. Once it gets moving it has some good power I guess. Valves are set right & whatnot. Not the increase in power I expected but it is what it is. And the carb adjustment! Just can't seem to get it dialed in. So frustrating. It's been like this ever since I installed that Malossi kit. See kids this is what happens when you mess with stuff.

So I've been contemplating an engine swap to a 150. A 150 would have enough power for me without me having to mess with it so I could keep it stock and therefore have none of this carb trouble to have to sort out. I don't really want to get a new scooter, don't want the hassle of finding one, registering it, etc. I can swap the engine out pretty easily. What else would I need besides the engine and a carb and an ignition? I know I would also need a rear shock to go with it.

Thanks for any help with this. Regards

You would need to swap the wiring harness, ECU, immobilizer antennae, and carb to start the list. Probably easier to just buy an LX150 or ET4.

It sounds like your carb problem is dirty pilot jet or A/F screw adjustment. How is it off idle when the enricher is still running?

Trying to avoid having to go downtown to DMV. Covid has made it even more unpleasant. This is why I'm swapping vs just getting a bigger scooter. Also 50s get to park on the sidewalk anywhere in the city. Besides, I like this scooter. No 150 donor scooters available here locally (and no cheap recovered thefts or totaled out scooters either) but many decent used engines on eBay right now, and all of those other parts too. I got plenty of tools & know how. But I still can't conquer that carb. It's a brand new Keihin carb too. Other carb was fine so now I got two good carbs. Yeah I also bought a new Piaggio CDI, original was good as well so I now have two good CDIs. I've done an 80 jet, didn't work out and also a 85 jet which did not work out.

Thanks for your thoughts on what may be the issue with the carb. I've dicked around with that adjustment screw for so long now I'm fed up. While the enrichment device is working the scooter moves off just fine. However at that point the idle is slightly higher anyhow so that's why. It's almost as if the idle stabilizes at what I would think is the idle, but then it drops even lower to a lower idle speed but holds steady. It is when moving off from this that it bogs and I have to feather it. So there's like two idle speeds if that makes sense. It's really weird.

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Possible accelerator pump sticky? or one thing I have going on is I am using some of the Chinese (maybe knock-off) Keihin carbs and the metal tab thing that engages the pump piston down when you throttle is not set consistently from carb to carb. So there is a delay between rotation of throttle and when the carb throat gets a squirt of gas. I have one where this is noticeable and my plan is to take off the carb and re-bend the metal a little so it's more instantaneous from idle. Good Luck.

Your cam timing could be off a tooth, especially if it doesn't seem much quicker than it was stock. If that's fine, I would try a 78 main jet.
Also, I would clean the jets again, then try to set the carb after the engine has been running for a long time. Even on brand new stock carbs, I've seen trash in the jets, and it doesn't take much for the pilot jet to clog.

If the carb has an accelerator pump, I'd try to adjust it so it kicks in sooner. If that carb has a slide and needle, I'd try to move the needle up a bit in the slide, so it runs richer as the slide starts moving up. Pretty clearly you need more gas. If the needle jet is replaceable, might also help to run a slightly larger needle jet.

I'm guessing the ignition timing is not adjustable on that engine. If it was, I'd suggest trying to advance it a few degrees. Back in the old days of adjustable ignitions, an engine that 'bogged' off idle sometimes had the ignition timing a bit retarded.

Do you suggest that he has to reprogram also the ECU?
It should have done so from the start of the change.

But:

Could it not also be that it is not the carburetor but (due to excessive increase in power) premature wear of the transmission belt? If it is releasing filaments in the crankcase of the transmission, the variator would be jamming preventing the engine from revving up.

I do have an offset key to advance the ignition timing 3 degrees. May try that. Don't think I got the cam timing off a tooth as it seems pretty hard to do given the marks being so obvious. I took my time and I'm sure I got it right. And would not the valves contact the piston if that were the case? Scooter runs great other than the off idle stumble. I installed all these upgrades and have been riding on them for two years or so now.

Got no ECU to reprogram; it is a 2007 carbureted scooter with a CDI ignition, and belts are wearing normally. Neglected to mention I did the Malossi Multivar upgrade also.

I did not intend to say the scooter has no more power than it did stock. It certainly does have more power. I no longer have to jump off and push it up the 20° or so incline I encounter on my daily commute as I did before I installed the upgrades. I just expected more I guess. But I have owned many Ducatis and currently own two so I may have unreal expectations in that regard.

Try the original exhaust. A little back pressure can help.

where are you located? i may be able to help... with a 150 conversion, that is...

-g

Thanks G, I'm in DC.

Anyway I think I'm going to try some of those suggestions; maybe go down to a 78 main jet or put the original pipe back on. Might be that the TK pipe just isn't tuned very well to this engine spec, or I'm too large on the main jet but I've been watching the plug and it never gets darker than a light grey tan so who knows as I sure don't. I also forgot to mention I replaced the fuel and vac hoses along with the fuel tap. Bought so many parts for this I forget a lot of it.

Thanks all who responded.