Modern Vespa

Hello all,

Recently purchased an LX50 2 stroke having always had old Land Rovers and have absolutely loved it: very little maintenance (compared to a Landy); great fuel consumption and total smile-factor.

Previous (and only) owner had derestricted, so it did 45mph ish and generally ran really well.

However, original exhaust well past its best and blew a hole: time to replace.

Ended up going for a technigas original pro, as wanted to keep as factory look as possible.

This meant deleting the SAS system that feeds into the exhaust (no problem thanks to threads on here already)

Exhaust fitted perfectly; was pre-derestricted by seller (removed 'cone'); Vespa running like a dream with a bit more poke.

However, now major problems!

Vespa conked out downhill at nearly WOT near 40mph; pushed home. Started at home perfectly; rode around to check all fine. Rode to work this AM, all fine, no hesitation.

Rode back home today, same again! Conked out downhill. Now will not start and have a flat battery (but won't start on the kick either.)

Spark plug a healthy chocolate brown; plenty of fuel and 2 stroke oil.

I am thinking new exhaust potentially requires up-jetting? Running too lean at top end? But, I thought previous owner's mechanic would have done this on original derestriction?

I have another spark plug to put in later today. It runs so well on start up and has been untouched until this point. I know a new exhaust changes this slightly but didn't think I would have to make carb changes; it's not a sports exhaust!

Any helpful advice much appreciated- not sure of any Vespa people here in deepest Cornwall to even take it to and hoping I can sort by myself!

Dom

an aftermarket exhaust will require an upjet. not massive, probably just a few points. barring that, you may be able to get away with raising the needle instead. however, I'd recommend going up a few to be safe.

Thanks for that: I guess I thought I might get away with it but an upjet is probably the way to go. Anything else worth doing whilst in the carb?

Also, does any idle and/or mixture screws need adjusting after a jet change?

Cheers for the quick reply!

The plot thickens! So upjetted: was a 66 and went to a 68 as that's the largest I had. Cleaned and removed everything in the carb whilst it was out. BUT whilst removing fuel hose what seemed like the entirety of the fuel tank emptied; strange as I thought it was vacuum operated.

Thought I'd replace the petcock, which I did and now the bike will not rev at all; idles fine but even the slightest twist of the throttle stalls her.

Now my first thought is- not enough fuel to rev at anything above advance.

I know I committed a cardinal sin in changing two things at once. Any thoughts?

Put old petcock back in?

Hi,

I'm not a mechanic, but some thoughts from my (limited) experience before the experts get to this.

The old petcock should shut off so that was a good change. Providing the new one is working properly (not a given) that should be good.

Are the fuel and vacuum lines OK, if original these would be quite old now and could cause problems.

The jet is quite big for a LX50 2T, they come with a 53 so to jump to a 66 or 68 deristricted with CAT removed seems a lot to me.

However as it was running fine with the 66 before the exhaust change that seems odd, I would have thought something like a 60 would have been about right. Might be worth re checking it was definitely a 66 with a magnifying glass as some of the stamps aren't that clear?

Saying that when the jet is too big they tend to splutter a lot rather than cut out.

If it were me I would also be checking the carb is all back together right and seals in the right place etc.

This is of course assuming it still has the standard Dellorto 17.5 carb, standard air filter and does not have a 70cc kit fitted?
If it has the air box removed and a sporty air filter on that would explain the large jet.

I would avoid messing with the mixture, idle screws as it was running fine before.

As you mentioned the battery had gone flat I wonder if that might be part of it as they can play up when the battery is weak.

I'd be really interested to hear how you get on with this for future reference.

Hi- thanks for the advice it's much appreciated!

I had also thought that the 66 was a large jet size. It seems like the previous owner had derestricted it by removing the gold plate on the air intake on the carb, adding the 66; removing the ring on the variator(can't think of the correct name) and part of the exhaust was crimped and welded shut- however the SAS system was still fully in operation on the stock exhaust.

Exhaust blew a hole, I thought in buying a more 'standard' exhaust I'd have less trouble!

In positive news I got it going today and it revved up to full power; however I'd still say under WOT it feels slightly choked akin to fuel starvation.

It didn't start immediately and needed to spin the starter for a bit to get it going. It then ran for 30 seconds and then died again.

Any more advice appreciated! I've check for air leaks; replaced petcock; checked fuel and vacuum lines.

It's a standard air box/filter and standard head- not a 70cc. Stock dellorto carb.

Large jet would suggest plenty of fuel I'd have thought; but maybe the 68 is too large? I was worried changing exhaust without upjet would end up with running lean and running the risk of a seize.

I reckon if I sprayed easy start it'd get going again, but at this point that seems like a plaster rather than the cure.

Cheers!

I found this useful

https://www.pedparts.co.uk/blog/how-to-derestrict-euro4-piaggio-typhoon-50cc-2-stroke-scooter

Your LX is probably a Euro 3 so it's not all relevant but a they jet a fully derestricted pre Euro 4 with a sports pipe fitted at 68, so yours would be lower than that.

My Piaggio Typhoon is pre Euro 3 so no SAS or Cat in the exhaust plus Dellorto 17.5. The stock jet on that is 60.
I derestricted by taking out the variator ring, cutting and welding the exhaust disrupter pipe, (carb plate had already gone).

That's basically the older version of the LX engine and it seems to run really well on a 62 or 64 and you can feel it pulling throughout the throttle range, in fact it's noticeably quicker than the LX or ET2.
I went for the 64 as it's better to have the biggest one it runs well with. I also run mine on super unleaded if that makes a difference.

The LX runs great as it is so I haven't fiddled with that and the ET2 has a Dellorto 12 carb so has completely different jetting.

If it were me I'd try putting the 66 back in see it that helps.
From your description it sounds like it could be too rich at WOT which would cause it to bog down a bit.
Might also be worth checking what position the carb needle is set to, middle is standard I believe.

All of mine (after they have been sat a few days) stutter a bit with throttle when I first set off but it usually sorts itself out by the end of my road, so I assume that's just what they do.

Is the carb float valve OK?

Just to end this as I always hate when you never know what happened!

So, after getting her running reasonably well, it was a pig to start if left stood overnight; a quick key off and on again no problem but any length of time- nada.

I looked back at the advice (many thanks) and thought it must be fuel/petcock- despite literally just renewing. I replaced vacuum line, got fuel on sucking but just wasn't convinced. So, I replaced with a standard on/off fuel tap, no vacuum required.

What a difference! Even with the vacuum line open (I know, massive air leak) it started and ran so much better. Having now fitted those little rubber covers for vacuum lines from eBay, I have a steady idle, a proper fuel/air mixture and power through the revs.

I can only guess I had some vacuum but not enough to really get the fuel flowing.

So, thank you all for your advice and thoughts, they are much appreciated! And… don't trust a new vacuum petcock!

Great news, thanks for the update.