Many many BV 500’s suffer from poor performance after about 3000 miles on the clock. The symptoms include: stalling, surging at low speeds, poor acceleration, low horsepower etc. Looking in the service manual is an effort in futility since all of these symptoms require the Piaggio service computer to diagnose. The problem is usually a design issue that fortunately is very easy to fix. Most units have been built without hose clamps on the high pressure fuel line hose coming out of the fuel pump located in the fuel tank. It seems that the problem started with the introduction of gasoline in North America that is blended with Ethanol. It appears that the blending of alcohol into the gasoline causes some breakdown in the fuel line. This causes a loss of proper pressure in the fuel line. While this seems like a serious design error on the part of Piaggio, forget the blame game for a minute and make sure your BV does not have this issue. Some contributors here on Modern Vespa have indicated that they are not only installing hose clamps as this project report shows, but also replacing the fuel line itself. The recommended fuel line and clamps are available at NAPA Autoparts. The proper part numbers are:
NAPA submersible 5/16" fuel line hose (part # H209)
NAPA high pressure hose clamps (part # 705-1226)
I would check for this issue this even if you have no apparent symptoms. After doing this repair, my scooter ran better than it ever did. I firmly believe that it was a parasite on my scooter’s performance from day one.
I would strongly recommend that you wait until your fuel tank is nearly empty before doing the following inspection/repair.
The inspection and possible repair consists of pulling the fuel pump/fuel tank sender/fuel filter assembly out of the fuel tank and seeing if there are hose clamps installed on the hose coming out of the fuel pump. If they are missing, it is a simple matter of installing hose clamps right over the hoses.
#2 Phillips Head Screw Driver
#2 Standard Blade Screw Driver
2 ea 10" tie wraps (optional)
(possibly) 2 ea 1/2" (12mm) ID metal hose clamps (NAPA Part #705-1226 or equiv.)
(Optional) Replace fuel line itself (Napa Part #H209 or equiv.)
Set scooter on level ground up on its lift stand. Open fuel door. Unscrew fuel tank cap. Remove rubber shield around fuel tank mouth. Now remove four screws. Two are inside the fuel door the other two are at the extreme front top corners of the black plastic saddle framework around the fuel filler door. Lift the fuel door end of the “saddle” and then urge the saddle out from under the lip at the rear of the saddle. Then tip the rear end up and over and off to the left (as looking forward). Screw the fuel cap back on to keep crud out of the tank. Things should now look as in the picture at Fig 1.
You can see there are two hoses that are connected at right angles into the fuel tank. Where each hose connects, there is a small collar ring. Press downwards on the ring while simultaneously pulling upwards on the respective hose. It should come loose. It will likely leak some fuel when it disconnects. Have a rag ready! I used a tie wrap on each one to hold them up and out of the way. Now disconnect the cable. I tucked it under the fuel cap. Things should now look like Figure 2.
There is a screw collar around the fuel tank sender assembly. Use a standard blade screwdriver placed against the ribs on the collar and tap lightly with a hammer. Unscrew the collar. Things should now look like Figure 3.
Rock the fuel tank sender assembly back and forth while pulling upwards. I assure you, it will break free and start to come up and out. Once it comes up, you should be careful while lifting it up so as not to damage the tank float (the thing that figures out how much fuel you have for display on the fuel gauge).
There is no need to pull the entire assembly up and out, I would just hold it up with a string or weak bungee cord attached to the handlebars while working on it.
Look at the hose below the white lid. There should be two hose clamps on this hose like in the picture below. If they are not there, YOUR SCOOTER IS DEFECTIVE…..so install some! Buy metal hose clamps for a ˝” (12mm) hose. Unscrew them completely and wrap them around the hoses. They should be quite secure, but be careful about over-tightening them. You are wrapping around plastic fittings. Your fuel tank sender assembly should look like Figure 4.
It is basically the reverse of the disassembly. Things to be careful about... The rubber ring that is around the white cap, tends to get folded over while reinserting the tank sender assembly. Be real careful that it slides in straight as you push it back down. Line it up in-line with the front/rear of the scooter and rescrew the collar. The two hoses just snap back in place. Reconnect the cable. Unscrew the tank cap, and replace the saddle cover. While installing the saddle cover, take care about the routing of the cable release for the fuel filler door. Install the four screws, the rubber seal around the tank filler collar, and the tank cap. You're done. GO RIDE!
Last edited by pdxscoot on Wed Sep 03, 2008 3:10 pm; edited 10 times in total