Modern Vespa

Hello,

My 1980 p200e recently ran out of fuel. It now idles well but dies when I accelerate. I believe it is being starved of fuel. I checked and cleaned the filter on the carb but now need to do the same for the filter under the fuel tank. Do I have to disconnect the fuel tap to get the tank out? Is there a link that someone can point me to that details how to get the filter off?

Thank you.

Why would you think it is starved for fuel? Why don't you pull the jets and clean them out first before pulling the tank. While you are at the carb , pull the banjo and check for good fuel flow.

Thank you for the response. The reason I think it is starved of fuel is that prior to running out of fuel, it ran fine. The tank is a bit dirty. When I checked the carb filter, I took the main jet out and cleaned it. I did not take the idle jet out however.

I should have followed that up with, I'm open to other suggestions.

I second a full carb clean.

If you want to see if your carb is being starved, open the fuel tap for a minute and then start your scoot. There will be enough gas in the hose and carb that the scoot should run perfectly until it uses up more gas than the tap is supplying. Then it would starve out. If it runs shitty from the get go it's not your tap and you should clean the carb.

If it ran out completely, there may be an air bubble in the line that will slow the flow down to a dribble. But loosening the banjo as Tierney suggested will tell you.

Thanks for all of the responses. I cleaned the carb (jets, float bowl, filter, etc). it then started pretty quickly and idled well. It also ran pretty well. I took it out for a ride and after about a mile, it started to die. I remembered that it was still low on fuel so I moved it to reserve and it ran fine. After adding some fresh fuel, I moved the tap back to normal and it ran fine for about a mile. it then started bogging again under acceleration. I moved the tap back to reserve and it ran better for about a mile then started doing the same thing. Fortunately, I was close to home. When I got home, I killed it and then started it again and it idled fine. I turned the tap off and let it continue idling until the fuel ran out.

Any suggestions? Again, thank you.

If you haven't already done so you must positively eliminate fuel starvation caused by the tap, the fuel line, any filters, and tank breather problems. This is easy enough to do by disconnecting the line where it attaches to the carb and observing the fuel flow. Also make sure that the fuel line routing is not too close to the hottest parts of the engine. Assuming the flow is OK ( anything better than a dribble is probably OK as long as its continuous ) you can also check the fuel that comes out for contamination both solid and possibly water.

Then you are back to the carb so first check for contamination in the float bowl then check the jets as you have done before. Also check the float bowl breather to make sure it isn't blocked or , if it has a rubber pipe, make sure it is not kinked.

If none of the above reveals any problem and makes no difference then maybe there is an issue that is not fuel related.

I'll just throw this out there: my Rally had a problem where it would start and idle fine but die when I gave it any gas. It turned out that the wiring from my stator was rotted. I replaced it and the only time I've had that problem since was when one of the wires to my CDI flexed to the breaking point because I crimped it badly.

I vote for a plugged fuel tank vent. See if it will run with the fuel tank cap loose.

It's one of those things that seems silly until you see it happen.

Again, thank you for all the replies. I disconnected the fuel connection at the carb and turned on the fuel. It seems to come out with more than a dribble.

I cleaned the carb again. All seemed to be working well on the most recent ride (only about 3 miles). I'm going to take it out for a longer ride which is when the issue began last time.

I really appreciate this site.

Hi Corleone,

I had exactly this problem and tried many things before I solved.
In my case it was just a badly and slightly too long fuel line.
It was hard to diagnose because fuel flow looked fine when I had the tank out and the fuel line point straight down.

I would double check your fuel line length and path to make sure you are not making it difficult for fuel to flow into the carb.

Raph

^^^^^Good advice. With the banjo fitting removed and held level, away from the carb, fuel should spurt up and out slightly, much like the flow from a miniature water fountain, not a dribble. Crude and messy, but quick and easy.

After much experimenting, it's amazing what a difference line length and routing make. A good dribble works fine until fuel starvation on a sustained high rpm run. A wide open, stock P200 needs about one gallon per hour fuel flow.

As Raphael stated, the flow has to be measured as installed at the banjo, not with a line hanging down. The water fountain effect is flow up and out the small hole at the top exit of the barbed fitting. Weaker water fountain with tank near empty.

Thank you for the suggestions. I hope to have some time this weekend to experiment. The fuel lines are the original lines - will that make a difference?