My 1962 Vespa GS 160 Mk 1 cinstantly floods from the carb. Have removed stripped and cleaned, replaced gaskets, no different. Bought a replacement carb, stripped, cleaned and replaced gaskets, still flooding and cutting out. Bought a new petrol tank, made no difference. What is causing the problem please. Thanks

If its a flooding problem then its a carb issue, and what you have replaced wont have effected the carb. I'd say you should either try stripping the carb and cleaning or replacing the internal carb gaskets. its probably just a sticking needle valve.

1. To correctly fix this the carbs will have to be removed from the rubber spigots completely and moved out of the way.
2. finish unscrewing the loosened screws and remove the rubber spigots and make sure to note which way they go so that they can be put back on the same way.
3. clean the back of the rubber spigots with laquer thinner or acetone and let dry for a few minutes. Also clean the head surface that the spigot attaches to.
4. apply a thin layer of gasket maker rtv or other suitable rtv to the back of the spigots and tighten them back down to the head.
5. wipe the extra rtv from inside and outside of the rubber spigot where it comes out of the mating surfaces.
Re-attache the carb and adjust the idle if needed.

If the rubber spigots are not sealed and tightened down, they can cause varying idle, popping throught the intake and exhaust pipe, hard starting, and bogging

would think you havnt got the needle set right it is just flooding the carb, strip and redo

It sounds like a stuck float in the carb, this my require a carb rebuild.

Probably best to replace both the gaskets between the carb and the carb box and between the box and the engine casing.

It sounds like your floats sticking in the carb leaving it open all the time. take the carb to bits and clean it replacing all seals.

I had the same problem - actually more than one problem:
1) Floats in the carburetor bowl (at the bottom of the carb) are getting stuck. Remove the carb; carefully disassemble the bowl & float assembly (pay attention to gasket orientation and don't lose the needle valve that the float-tab presses on!); use a carb cleaner from AutoZone or similar, and a toothbrush to clean all the parts. If carb is not too dirty, leave the jets and mixture-adjust screws alone (otherwise will have to re-adjust later).

2) Overflow tube is plugged (hence fuel in the cylinder instead of on the ground). Clean both ends of the brass-looking tube from inside and outside the carb bowl. Make sure you can blow through it or it is still plugged. Toothbrush and carb cleaner should do the trick. Replace the short flexible tubing that connects to the overflow on the outside of the bowl - transparent polyurethane tubing is less than $1 per foot at your local ATV/motorcycle shop.

3) Air Vent tube is plugged. Same thing as the Overflow tube but mounted higher up in the carb (not in the bowl). Clean it the same way and replace the flex tubing with another short piece of polyurethane.

4) Make sure the float-tab and needle-valve move smoothly. Mine was catching and getting stuck so I carefully "polished" the face of the tab with 400-grit emery paper, and then made sure to clean the area from grit. Smooth as a hot knife through butter now.

5) Set the float level by CAREFULLY bending the tab that pushes on the needle valve. On my 1981 175MX, float height spec is 21mm when just making contact with the needle. Yours may be different though.

6) Reassemble the carb after making sure all dirt and debris are gone. Use a new bowl gasket or at least put a good gasket-sealer compound on the old gasket. Attach the short lengths of transparent polyurethane tubing to the Overflow and Air Vent. When installing the carb, the Air Vent tube should just be 2" long and point out to the side; the Overflow tube should route through the frame near the swing-arm and point down to the ground.

7) MAKE SURE the Oil Feed tube coming from the AutoLube oil pump is connected to the carb (brass-looking fitting toward the cylinder-end). I replaced mine with transparent polyurethane tubing (different size than the Air Vent and Overflow), so now I can see that oil is being presented to the carb!

8) If the carb was nasty-dirty, you may need a new air filter. Mine was disintegrating. I recommend also putting an in-line fuel filter between the petcock and the carb, again using short lengths of TRANSPARENT polyurethane tubing (so you can see that fuel is flowing). You may also need to adjust & prime the AutoLube oil pump.

I highly recommend getting a Clymer manual (check eBay) which shows all these procedures and gives you the right specs for float height, etc. based on your model / year.

It sounds like the float is sticking in the carb. Since the carb is higher than the fuel tank it pulls the fuel in by vaccum of the engine. when running at high rpms, it can burn the fuel thats flowing into the carb, when you idle down, the bowl of the carb is filling up with fuel faster than the engine can burn it and causing it to flood. Then when it shuts off at idle it does not want to start back up because it is flooded. To make a long stary short, pull the carb and give it a good cleaning and your problems should be solved.

The owners manual says to use gas with Octane of 90.