Vapour Lock! - Rover P6 3500 - davidcanning
Hi ,I have a Rover P6 3500 which runs a treat . In heavy traffic however its different story. Cutting out ,misfiring comes to mind. Leave it to cool down and im away again. Ive been told its vapour lock . New to me this is. How do i over come this please?
Vapour Lock! - Rover P6 3500 - Number_Cruncher
Typically, this means that the fuel is getting too hot in either the pipework, or in the carbs themselves, and locally boiling.

Things to check include making sure that the routing of the fuel feed pipes are correct, and that the don't go too close to the exhaust, and that the correct insulating plastic spacers are in place between the carbs and the manifold.

Your fault could be caused by other things - I would also check the entire fuel and ignition systems very carefully.

Vapour Lock! - Rover P6 3500 - 659FBE
Your vehicle was designed to use a fuel with a higher boiling point than presently available fuels have. There is a solution.

The Brazilians were faced with this difficulty when they blended a significant proportion of bio-ethanol with their mineral fuel, lowering its boiling point. They developed a very clever vapour separator - I have trialled one of these and it works impressively well as follows: Imagine a vertical plastic cylinder 1.5" dia by 2.5" high. About 2/3 of the way up, the fuel inlet is positioned so the fuel enters the cylinder at a tangent, thus spinning the fuel around inside. At the top centre is positioned the return line to the vehicle tank - route for surplus fuel and vapour. The outlet to the fuel system (Stromberg carb in my case) is centre bottom. The centrifuge action of the fuel spinning in the pot causes the heavier fuel to stay on the outside, falling to the bottom whilst the lighter vapour stays in the middle and is drawn off.

The only trouble is that I can't for the life of me remember who made it - it was an official mod on my 1982 SAAB and worked well. It was made of white translucent plastic and had "Made in Brazil" moulded into it. Try Google or SAAB owners' club.

Vapour Lock! - Rover P6 3500 - jc2
Ford used a similar item in the days just before Fuel injection;it may also be made worse by a combination of a warm day and winter fuel.
Vapour Lock! - Rover P6 3500 - mike hannon
An electric fuel pump in place of the standard mechanical one often works if you don't mind sacrificing originality.
I was plagued with vaporisation problems with my P6B as well until, luckily, Serck Marston managed to find a high capacity radiator in Edinburgh and get it to Dorset for me. Cured the problem and it never recurred.
Vapour Lock! - Rover P6 3500 - jc2
Bosch also made a tiny in-line electric pump thay could be fitted in series to overcome this very problem.
Vapour Lock! - Rover P6 3500 - nick
An electric pump often cures this problem. Bigger capacity radiators are readily available which may help, they're a good idea in any case. Rimmers stock them but you may find them cheaper elsewhere.
Vapour Lock! - Rover P6 3500 - Screwloose

I had the misfortune to run a 3500S in the baking summer of '76. It's the fuel pump that causes the problem - and the lack of a return line. The most successful quick-fix was to wrap the pump in a [well-secured] cloth and soak it in water.

Maybe a deflector plate to stop the fan blowing hot air straight at the pump would help? Fitting a proper return line would be the best bet. As said; that wing-mounted unit off a carb Sierra might fit the bill.

Ask Honest John

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