Vespa Pre 1979 Large Frame Engine Work

Oil Mixer (Autolube)

The Vespa 150 Super was the first Vespa to have a separate two stroke oil tank with a mixer device to correctly mix oil and gasoline in the engine intake. For the first time Vespa owners could put in a quart of oil through one filler cap, and then fill up with typical gasoline in the main tank, with no fussy mixing at the station. There were two systems used over the run of the Vespa engine. The first system is noted in this section and was used on any bike with autolube up to the P series models.


The system is driven off a small gear on the crank which powers a small oil pump by a worm drive. The pump is located in the carb box just forward of where the carb should be. The carb boxes above are of the two different systems. On the left is the older system used up to the Rally 200. On the right is the P series system still in use today. Both systems have an arm which connects to the throttle linkage so the amount of oil pumped is in relation to the engine speed from the drive and the throttle position.


Above is a shot of the underside of the carb boxes for both systems. Again, the older system is on the left and the newer system is on the right. Both use the idea of a pump with a small groove in the bottom of the carb box to get the oil feed from the pump to the carb. The drive hole from the worm gear is marked with a yellow arrow, the oil pumped from the pump comes out of the hole marked with a blue arrow, and then moves down the groove to the red hole where it enters the carb.


Once it comes through the carb box it goes into the carb where the blue arrow is shown, and is combined with the gasoline when it comes out of the hole marked with a red arrow, above the throttle slide.


Servicing the pump

There is really not much to service in the pump other than replacing the gasket and making sure the pathways are clear. To service the oil pump in the older system, remove the three flathead screws that hold the pump body to the carb box. Once these are removed you can carefully twist the pump out of the box.....


...and slide the oil intake line through the carb box body. Discard the old gasket as it should be replaced whenever the pump is removed.


Once the pump body is out of the box, have a careful look at it to see how it works. It is a little complicated, but once you understand it, it starts to make more sense.


The central drive gear can be removed by pulling it out from the pump body. Pay particular attention to how the throttle arm linkage connects to the circular piece above the gear, and how the slot in the gear aligns with the small dowel in the pump body.


The circular piece can also be removed from the drive gear to expose another circular piece which slides on a dowel to the main drive gear.


...and finally a small bushing between the two. I took this apart to see how it worked more than anything (I'm like that). For servicing make sure all the parts are clean, and the passageways in the carb box are also clean.


When you replace the pump back in the carb body always use a new gasket between them.


The drive itself is the only other part that needs to be checked. It is turned by a small gear that is on the end of the crank between the clutch and the oil seal. It is held on the shaft by the woodruff key in the crank end. In the picture above it has been removed. A second drive gear turns on a small shaft embedded in the casing, which ultimately tuns a vertical shaft via a worm gear. Check that all the teeth in all the gears are in good condition. Spin the gears to make sure the oil drive vertical shaft turns. It will turn very slowly.


If the shaft needs to be replaced it can simply be lifted out of the casing. Once the oil pump is back together you can test it by this simple test. First, connect the oil line from your bike to the carb box oil intake. Then, take the vertical shaft drive out of the casings and very carefully and loosely chuck it up in a variable speed drill. Insert the end of it into the underside of the carb and slowly rotate it in the counter clockwise direction. On the underside of the carb, oil should start to dribble out of the hole next to the drive hole (in the groove).

When you install the carb box, use a new gasket between the casing and the box. There are a bunch of different gaskets out there so make sure you have one that has a hole for the mixer drive gear.

Make sure the gear engages into the oil pump hole when you place the box down on the casing.

Finally, make sure the gasket you use between the carb has the hole punched out as shown above. If not the oil will make it all the way from the pump to the underside of the carb box and then hit a dead end. The hole in the gasket must align with the oil hole in the carb box for the oil to make its way into the engine.