P5B - lack of fuel when hot - rebuild pump or electric?

[shed]

Hi all,

Long time no post! All has been fine with my P5B so I've had no need to get the spinners out, until now....!

Driving around yesterday on the hottest day of the year (!) I popped into B&Q - after about 1/2hr returned to the car, and it wouldn't start, cranked fine, but not a sniff of firing up. Took the fuel pipe off the carb, and filter and cranked - no fuel / bone dry. Engine was pretty hot. Left it to cool after an hour tried again - nothing, eventually recovered after 3hrs, tried before ri was recovered, still nothing.

Pushed it back into the barn in disgrace last night. Went to start it today to give it a try - all fine!

Any ideas? Is this a common p5b thing? I've rebuilt the mechanical pump about 10yrs ago - is it worth going electric?

Thanks in advance,

Steve

[harvey]

Jun 22, 2017 15:33:42 GMT shed said:

Driving around yesterday on the hottest day of the year (!) I popped into B&Q - after about 1/2hr returned to the car, and it wouldn't start, cranked fine, but not a sniff of firing up. Took the fuel pipe off the carb, and filter and cranked - no fuel / bone dry. Engine was pretty hot. Left it to cool after an hour tried again - nothing, eventually recovered after 3hrs, tried before ri was recovered, still nothing.

Pushed it back into the barn in disgrace last night. Went to start it today to give it a try - all fine!

Any ideas? Is this a common p5b thing? I've rebuilt the mechanical pump about 10yrs ago - is it worth going electric?

It does sound like fuel vapourisation, it was, as you say, the hottest day of the year. You would think it would restart after 3 hours standing, but if that was 3 hours standing in direct sunlight in the heat of the day, then it doesn't surprise me that it didn't.

You could fit an electric pump in addition to the mechanical one, just turning the electric one on in situations like the one you experienced yesterday. Before getting too involved though, make sure everything in the cooling system is in top order.

[lagain]

The problem is that if the fuel has evaporated in the fuel line it has to be pumped all the way from the tank and it was exceedingly hot.
I would wait and see if it happens again. The advantage of an electric pump is that the engine does not have to be turning to pump the fuel through. If I turn on my ignition the electronic pump starts and I can hear the fuel dropping back into the tank, so I know the lines are full.

[Phil Nottingham]

No problem with ours on hot days since I fitted a Facet pump in 2001.  Did often falter in hot weather in slow moving traffic before

[shed]

Thanks for all the replies gents, I think I'll replace the mechanical pump with a blanking plate and retrofit an electric pump.

Any recommendations for pumps? Jon Wadham does a puller I believe to fit up front. I presume sequence would be tank > fuel line > electric pump > fuel line > regulator? > fuel line > carb. Do I leave the original fuel return intact? What size fuel line do I need to order?

Thanks for the pointers, as ever!

Steve

[Phil Nottingham]

Loads on SEARCH with pics - Facet is the best option fitted underneath near the reserve tap or low down at the front. Reg is not required and filter must be before pump - leave the existing one in place

[enigmas]

A few observations/recommendations from OZ, where weather in the 30°C range is often just another sunny day.
If you are having issues with fuel vaporisation fit an electric fuel pump away from the heat source (obviously the engine bay) and also ensure that there is a bleed return at the carburettor fuel inlet (close to the bowls). If the car doesn't have a bleed return, make one using a simple brass T piece by soldering one outlet close and then drilling a 1/16" hole...this is now the bleed return maintaining a constant flow of fuel within the line and eradicating vapourisation. Plumb this to your tank filler with a 1/4" return line. Do not use steel or copper fuel line any where as these absorb heat...as does the mechanical pump bolted to the engine. Use good quality synthetic rubber fuel hose within the engine bay. This doesn't absorb radiated heat. Fit a an efficient mechanical fan or preferably a flex fan (most efficient) and construct a shroud so that air is pulled evenly from the complete radiator core. Note that 1960s muscle cars used this simple technology very effectively and stayed cool in hot climates, (California).

An efficient mechanical fan keeps a constant flow of air passing over the engine block at all times something electric fans don't do!
The above works for my 4.4 litre V8 powered P5 coupe in the hottest of summer weathers often reaching into the 40s.