I am using Vespa PX 150.It is using Contact Point system. The issue is it is consuming fuel more than average and the plug is full of carbon after approx 50 Km.The engine not start unless I clean the carbon from the plug. As I clean the carbon from the plug then my scooter starts . I am using NGK spark plug.There is no extra weight on it that u may say it is the cause of more fuel consumption.The air pressure in the wheel is also ok.

I also regularly tune my carburetor after every 400 KM.

Kindly guide me that that should I change my carburetor or its jets or there is any other problem.


1 Answer 1


Your experiencing fouled plugs. Fouled plugs have carbon buildup that grounds the electrode of the spark plugs over the ceramic with carbon. The carbon buildup occurs because the AFR (Air Fuel Ration) is too rich. This makes the combustion process, when you fuel is burned, too cool. Since combustion is too cool carbon buildup occurs on your sparkplug and now you can't start your scooter.

There are a few things to check and most of them involve cleaning up your carburetor and your air intake.

  • Validate that the NGK sparkplug that your are buying is the correct one for the scooter. If the plug is too 'cold' because it is incorrect you can experience plug fouling.

  • Clean your air filter. Make sure it's not too restrictive. You best bet is to replace it if yours is dirty and clogged. Purchase a foam air filter you can clean and re use if they are available.

  • Points are cheap and the condenser can go bad and not provide enough electricity to your coil to have a good spark. A good way to eyeball if your spark is bad is to remove the sparkplug from the scooter and put it in the end of your sparkplug wire. Allow the sparkplug to rest against the engine of your scooter so it's grounded and turn it over. If the spark is orange you have an issue. If it is whiter or blue, it's fine and don't worry about the points.

  • Make sure your floatbowl on your carburetor isn't leaking. If it is, it can fill your crank case with fuel and when you run the bike it's adding additional fuel to your mixture and fouling your plug. You would need to remove your carburetor and then your floatbowl and clean out the carburetor with carburetor cleaner. Use the little red tube that's provided with the can of compressed carburetor cleaner to squirt into any brass jets your have as well as your carb needle and seat where the fuel can leak into the system from.

Once you have it put back together make sure any vacuum lines are reattached to their proper nipples so you don't develop a lean condition from an unmetered air leak.

If you have additional questions, please open a new one. Remember, you are getting too much fuel from either an a restricted air flow or a carburetor issue more than likely. If you need direction on timing the scooter because you want to replace your points, that's an entirely new question and feel free to ask.


  • As @sweber states below in his comment. Check that your choke is not sticking. Your problem could be as simple as that.
  • 1
    Thanks a lot for the prompt reply. Appreciate you.I am using my Vespa PX 150 since many years but such kinds of things I never notice. Like plug type which is the most important thing.Cold and Hot plug these are two different types of plug which I have understand.For slow speed ,normal driving Cold plug is good and vice versa. There are many points which i may discuss.Like Plug type but 1st i shall look into more the points which u have mentioned i.e carburetor concern points.
    – gardenair
    Jan 27, 2016 at 11:12
  • 1
    One additional point: Check the choke module at the carb. It should get warm after a few minutes, and the bolt inside should move out a few millimeters. (measure it, it's too slow to notice).
    – sweber
    Jan 27, 2016 at 11:47

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