Si 24 carb setup


Ive just fitted a DR177 kit to my PX and have used a 24SI carb straight off of a P2 with a 116 main jet. The bike is running ok (and starts and idles ok) but has a flat spot at the middle of the rev range and it feels as though its choked up and misses too. Ive got a standard exhaust and have checked the jets and filters are clean and the carb is secured properly and getting fuel. Ive also checked and the air mixture screw is turned out about 1.5 times.

Does anyone have any ideas?


Lee - Australia

my pleasure to know it works the way you like.

i planing put on my engine Px 125 Lusso kit DR 177 with carb SI 24/24 with Sito plus and I have this some problem how main jet put on may carb with this configuration.
I life in Poland and in my country prats to vespa is very expensive and i my buy via internet. I ridding on my vespa in this seson on the winnter i planing change my engine and i have all parts to my change.


I followed your advice - tried a smaller 110 jet, changed the plug to a NGK B8 and altered the timing and the scooter runs great!!! Many thanks for your help

Lee - Adelaide SC

Sorry to dig up an old thread. DR 177 kit fitted to VBB150. SI24 carb.  Only just rebuilt so running in but not too successfully. Scooter is cutting out but will run with air filter off. 118 main jet, is this too big? Would carb set up for a vbb be similar to a PX?

Hi Lee

Have you checked the plug to see if you have a nice light brown electrode? I know after fitting my Pinasco kit it can often take a while to get the slow running sorted properly with the mixture screw. Keep turning it out or in until you achieve the fastest idle for a particular tickover screw setting and then try the bike for a short distance and fine adjust 1/8-1/4 of a turn at a time until it feels right and keep checking the plug. Turning out is becoming richer, in is becoming leaner. Unsure of correct jetting for your kit but if you’re running in you don’t want to be lean. There are probably quite a few other posts from people with your setup for jetting info. Often pays to have a collection of slow running jets, air correctors, mixer tubes and main jets.

If it’s a newish machine with a soft seat these can restrict the breather hole underneath. If your standard exhaust is quite old this probably won’t help and may be choking the engine. If you change anything, just change one thing at a time otherwise you won’t be able to isolate the cause of the problem.

Good luck. AK

PS Don’t know anything about Cosa clutches and gearing set ups, do you? Just posted something last night.

Thank for information!
When I order parts via internet I will bought main jet 108 and

Thanks for the advice. The plug is a dark sooty colour and the engine seems to choke up at higher revs especially when it gets hot. The bike is run in now so I’ll try the smaller jet and see how it goes.

Also, is the standard timing 18?

Thanks again


hi cipiur,

i have the same set up. see the advice thats been given above.

i did the following:

NGK B8 spark plug
110 Main jet in 24 mm P200 carb
Timing set at 18

If you have a P125X or P150X the standard is 21°, on PX 125-150 the standard is 19°


I think first thing 116 main jet it is too big for your DR 177. Start with a 108 and depending on the result (check the plug with plug chop technique and feel how it rev at high rpm) go either for a bigger or for a smaller one.
Check if the plug is of a correct grade ( for a Bosh grade 4 8 for NGK, 24 for a Denso and for Champion sorry I still get confused with their numbers).
The timing should be at 18. It is important.
Start from this then let us know and we will see if other changes are necessary.

Add a 112 as well,you never know.[;)]