Modern Vespa

First off, I went through this whole carb adjustment thing a couple of years ago with my first 50s, but this time I'm looking for a couple of specific things.

My 50s is midly kitted, and as per my previous thread, I'm in the process of finding out what I have "under the hood". I now know, because I just took it out, that I have a stock dellorto SHB 16.16. I'll pull it apart to look at the jetting.

My rookie mistake, was that I started fiddling with it before noting the current settings. I did this because even though it was running well, It wasn't idling so well, and I needed to use the throttle at the lights otherwise it would stall. So I thought I'd adjust the idle screw...trouble was I adjusted the wrong screw and changed the A/F screw...Doh

So, my questions are;

1. Even though the mantra here is 1.5 turns to start, the article at vespa maintenance relating to a dellorto SHB 19.19 says to set it to 2.5 turns and leave it. Does anyone know if the factory setting of 1.5 turns relates to the bigger large frame carbs, and that my carb may have a different "factory" setting, [ not to be confused with the Spaco 2.5 turns ]?

2. Is it typical to adjust the carb jet to allow for kitting, with the other settings remaining the same. In other words, can I assume the A/F screw is still adjusted the same for kitted / non kitted engines, and that the additional fuel required for a kitted engine is taken care of with a larger jet? In other other words, adjustment is still 1.5 turns, [or 2.5]..kitted or not?

that mixture screw effects the idle jet only

if a engine is kitted then yes a slightly larger idle jet would be fitted and the the mixture screw would then be adjusted till the rpms drop fast @ idle and the engine has good response when taking off from a stop.

if air filter is not on carb or a aftermarket is used then a larger idle and main is needed to be safe

if you have a air leak then that screw can get you home without having to deal with a engine that "races"

pull the jets and write them down
make sure they are no jetex crap = use real dellorto jets

look for leaks
check all top end nuts and bolt for spec

when your engine was shutting off @ idle that was due one of the following:
- the idle stop screw being "out" to far
- a blocked idle jet
- mixture screw that was way too rich
- low compression due to gummed up rings / broken rings / blowby

Thanks Spiderweb, great info.

Just to be clear, the bike was running well apart from stalling at idle, so I agree that I need to go through the list at the bottom of your post. I was thinking it was just the idle stop screw too far out....

Took off the carb and gave it a through clean with carb-clean. Replaced the fuel line and in-line filter, and reinstalled.
Set A/F screw to 2.5 and idle stop screw to 2.5. Started on second kick. Warmed it up for a few minutes but idle was still too low. Ended up adjusting the idle stop screw a half turn and all is good

I love it when a plan comes together.....

whats your jetting at there Rod???

Yeah well, that's where paranoia sets in, because the idle jet is 42 and the main jet is 74....which just happens to be stock. Now I'm worried about potential damage, but I guess if I've been riding around at near WOT the last few weeks, it must be OK for whatever kit I have.

The kit can't be too extreme if its running so well? It must be kitted right?....a 50s cruising at 60 kph and getting near 70 kph?

I'm just back from a quick ride to McD's and it seems to be going real well...better than before if I say so myself.

probably has an ignition that is set a bit too safe



I once bought a scoot that the PO said was slow...

after I fixed the timing (was @ 12 BTDC and set up the carb correctly (along with the other basic improvements) the scoot woke up and flew.

Just had a good read through the "tips and tricks" thread...man there's some good stuff in there....anyhoo, according to one post by Voodoo, the stock jetting for a 50s and 90 with the SHB 16.16 is 63 main and 38 idle.

My jetting of 74 / 42 is stock for an SHB in a Primmy 125

Now I just need to see what it's powering...