Gas problem I think?

My moped starts up fine. It's when I give it gas it dies out. Then without a problem I can start it up only to have it die again when I turn the throttle. Not sure what's wrong. The moped is a Cimatti city bike 1977. If you have any suggestions I would appreciate it.

Re: Gas problem I think?

the starting and idle system is working fine .. These require small amounts of fuel and air.

But when you open the throttle to take off, the carb senses this and another internal system takes over.. and this one has problems.

Normally, opening the throttle would provided a balance of an increased amount or air and fuel.

The throttle plate or slide does open making more air available, but for some reason there seems to be no additional fuel available.. so the engine dies.

A common caused is a tiny piece of dirt blocking some orifice or fuel-jet inside the carb.. and a carb cleaning will clear it up.

Re: Gas problem I think?

Your motor is running out of gas (fuel) before you even get going. An older bike might have rust in the tank plugging the filter or the float level got moved somehow. The level of gas inside the carb has to be high enough for the motor suction to pull the fuel out through the different jets. Low speed uses small jets that can get plugged easy (but your engine idles so that does not seem what is wrong). To move at half speed there is a slightly larger jet that might be plugged. Then to go any faster than 3/4 throttle the main jet finally starts being used. It is quite large and hardly ever gets plugged. But the main jet often screws in and holds the intermediate jet which is the middle speed jet. Once I had a brand new bike with a full tank of gas and the air vent in the filler cap was plugged, no air in means no gas coming out so the engine dies, (there is usually a small air leak enough to let the engine idle.) If the tank was only 1/2 full it would work ok for about a half mile, stop, air would leak in then you could go another 1/2 mile etc.

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