1966 vespa - 2 stroke engine - revving at stops

engines

#1

I have been riding my new (old) scooter for several months now. sometimes when i come to a stop and push in clutch & brake my engine does not slow down. My hand is not on the gas. The engine is revving super fast and there is nothing i can do to slow it to its regular idling speed. It usually will fix itself after light turns green and i take off once more. But this can’t be good for it.


#2

Lots of possibilities:

  1. Throttle cable is sticking
  2. return spring at carb is broken
  3. dirt stuck around carb, jamming connections
  4. Vacuum leak somewhere
  5. Cold start circuit stuck

If you are going to ride a scooter this old, you have to learn to fix it yourself, because you will go broke paying someone. There are lots of spots on the Web with help for you. Google your model Vespa and the word “forum”.


#3

thanks! I will look into. I am planning on learning how to fix and maintain my scooter, maybe this will be my first challenge.


#4

When the throttle is closed on a 2 stroke engine it doesn’t immediately drop to idle. It will usually blat and pop and sputter down to idle speed but it requires several seconds. Does the revving you speak of last more than 5 seconds? Is the idle speed high enough to release the clutch and pull away from a stand still? If so, how fast?


#5

definitely more than five seconds, long enough to go through an entire red light sometimes, 30 secs- 1 minute maybe? and it is consistently high, no sputtering.

haven’t tried pulling away from a stand still yet, usually have cars in front of me. and when light turns green i usually go thru the motions and add gas as i pull away. but will try next time to pull away without adding any and see what happens.


#6

Air leak around intake is where I would look.


#7

The European 2 strokes that I am familiar with had carburetors with piston throttles. If the air filter was not functioning trash could be binding the throttle piston in its bore. You might look into the carburetor while twisting the throttle to see how freely the piston moves. A good spray of carburetor cleaner or even WD-40 might free it up if binding.


#8

Wow, this sounds exactly like me…I could have posted this myself.

I just rebuilt the LML engine on my 1966 vespa sprint. I was having the same issues. Let me run you through what I did to mine:

First, I rebuilt the Carb. You need to connect with the guys at Motorsport scooters. I live here in San Diego and they are right around the corner. But you could give them a call. They can sell you a carb rebuild kit. Change all the gaskets, float neddle, etc. Also make sure you change all the gaskets that sit below the carb. there are a few there, one on top of the reed and one below.

If that doesn’t fix it, then you probably have an air leak. There are two gaskets that it can be. do you know how to change you gear oil? what you want to do is drain your gear oil. if you don’t smell gasoline in this oil, good news. It is the flyside seal, which is not too difficult to change and doesn’t require you to drop the engine.

However, if you do smell gasoline, welcome to vespa baby…this means an engine rebuild. now keep in mind, you engine is not shot or anything, but this leak is from the clutch side seal, which is buried pretty deep in the engine. You are going to be splitting the cases and everything, so time to change all bearings, all seals. A lot of work…

I just finished this rebuild because of this clutchside seal. I would get the haynes manual plus “how to restore and maintain your vespa.” have those open throughout any of these jobs.

I hope all this helps. I put my engine back together and I am still having issues, but I think it is because I am having timing/mixture issues.

Vespas are AWESOME. Way to go and get dirty. Also, hit me up if you have more questions. I am new at this stuff too and it is good to talk to folks about their bikes.

douglaswelcome(at)me(dot)com


#9

Don’t know if this is anything related or not, but I recall the Vespa I had as a kid (probably about the same year as yours)used to accelerate and rev up when it was running out of gas. I always thought that was odd…and dangerous! Topping off the tank again would cure the problem.


#10

I was thinking it sounds like a sticking cable. Motorcycles and scooters do strange things sometimes. For example, on some bikes, the front brake will rub if you turn the handlebars to the side while backing up. Yesterday, I noticed my throttle sticking while backing up with the handlebars turned all the way to the right. For some strange reason, these things don’t happen when the bikes are moving forward. Go figure.

The next time this happens, try turning the handle bars all the way to the right, then all the way to the left and see what happens.