first: you better not open the engine by yourself. the chance to worsen the condition is higher than the probable benefit if you are not a skilled Vespa mechanic....it's NOT a snap, rather a major overhaul...- then I like to know: why do you think you actually need to adjust the valve timing?Valve Adjustment on Vespa Sprint 150 3V
Hi, Unionjak if you have changed your engine size, compression ratio, fuel delivery system, air filter size or flow rate, mufflers or exhaust system or a significant change in altitude your carburetors need re-tuning and if your fuel system (gas tank, filters, fuel valve, and carburetor) is contaminated with ethanol sludge, varnish, rust, dirt, water, etc. or your bike has been sitting for months or years without running these components must be "PROPERLY" cleaned and reassembled "CORRECTLY" before any adjustments can be made. Tuning your carburetor is fairly simple once you understand the basic principals. Your engine is a simple airbox sucking air in and blowing it out, it is finely tuned at the factory for maximum performance once you upset that delicate balance by changing air filters, camshafts or exhaust systems your performance may go down the and the engine may run poorly, you need to compensate the air-fuel mixture in the carburetor in order for the engine to run smoothly and at peak performance. If you are running multi carburetors you need to sync them first and make sure your air cleaner element is clean and dry for paper elements or lightly oiled for foam and meshed elements and properly installed. Here is how and where you compensate trouble: "TIP" if your engine "BOGS" you're not getting enough fuel.
1. Close to 1/8 throttle is managed by the air screw and pilot/slow jet.
2. 1/8 to 1/4 throttle is managed by the air-screw, pilot/slow jet, and throttle slide.
3. 1/4 to 1/2 throttle is managed by the throttle slide and jet needle.
4. 1/2 to 3/4 throttle is managed by the jet needle, needle jet, main jet, and air jet.
5. 3/4 to wide-open throttle is managed by the main jet and air jet.
6. A wide-open throttle is managed by the main jet.
If you are running lean, spark plug electrode color is white, the engine runs hot and feels like it is starving for fuel you need to go up on the jet size or move the c-clip down one notch. If you are running rich, spark plug color is black or dark grey, the engine runs cool, and bogs down when accelerating you need to go down on jet size or move the c-clip up one notch. When your carburetor is properly tuned for maximum performance your spark plug electrode will be a light tan color like coffee with cream. If you prefer fuel economy over performance you can go down on main jet sizes until a satisfactory level of lower performance is acceptable versus MPH, your spark plug color will be whiter and your engine will run warmer. These tuning adjustments will only make improvements if your intake and exhaust system have no air leaks or sealing issues and the entire electrical system is in proper working order and you have no mechanical issues.
For more information about your issue and valuable "FREE" downloads that you will need for viewing and printing please click on the blue links below. Good luck and have a wonderful day. http://modernvespa.com/forum/topic75894 https://www.youtube.com/watch?v=QlXTE2bLWMI https://www.manualslib.com/manual/825253/Vespa-Gt-125.html https://www.oemmotorparts.com/oem2.asp?M=vespa https://www.manualslib.com/manual/867725/Vespa-Gts-125.html
That is great price for the 2008.......The money You will save, by buying the 2008 will easily cover any problems that may arise......Vespas have a very high resale value.....I recommend an authorized Vespa dealer to perform any and all sevices to maintain the resale value.........
- first: get some starter spray and spray some in the air inlet at the air filter - then IMMEDIATELY start it. may need several trials.
- second: push the Vespa in neutral some meters until you reach a certain speed and then switch from neutral to the first or second gear - then push further with some speed until it fires up the engine.
you can do it best on a flat road or even better downhill....
The float pushes a needle that then stops the fuel flow make sure its not the needle thats sticking or what ever pushes on the needle is not sticking ! But if you are sure it is the float that is sticking a fine sand paper (320 ) can be used around the sides of the float to smooth down any rough bits .