I have recently bought a 1972 500L with 652cc engine, oil cooler & Weber 40, road race head oil cooler underneath back seat ( obviously outside) with disc brakes all round with a very highly tuned engine
My question related to the fuel pump, at the moment the car is using the standard mechanical pump, however this is making it very hard to start from cold, I assume it's due to the fact it only feeds the carb when the engine is turning over and as it has a Weber 40 this takes about 10 to 15 sec to fire up.
Am I correct in assuming fitting a push pump next to the tank will speed up the starting?
I also have noticed there is a spare copper fuel pipe blanked off at the top of the engine compartment the other end seems to go back to the fuel tank somewhere. Should this be connected to anything or is it some sort of breather pipe.

Abarth never used an electric pump in any of the 'road' versions of the 500--even the 695. There should be enough fuel in the carb for the engine to start from cold. Do you have a choke system? Having you tried giving the throttle a couple of slow pumps (to operate the accelerator pump) prior to cranking the engine over. If you give the engine a few seconds between pumping the throttle and cranking the engine, this will give the fuel time to start to vaporise--petrol vapour ignites a lot better than 'wet splodge'.
The copper pipe that you have found could be used (or possibly WAS used) as a fuel return system back from the carb to the tank.

ClassicFiat500 said:

I have recently bought a 1972 500L with 652cc engine, oil cooler & Weber 40, road race head oil cooler underneath back seat ( obviously outside) with disc brakes all round with a very highly tuned engine
My question related to the fuel pump, at the moment the car is using the standard mechanical pump, however this is making it very hard to start from cold, I assume it's due to the fact it only feeds the carb when the engine is turning over and as it has a Weber 40 this takes about 10 to 15 sec to fire up.
Am I correct in assuming fitting a push pump next to the tank will speed up the starting?
I also have noticed there is a spare copper fuel pipe blanked off at the top of the engine compartment the other end seems to go back to the fuel tank somewhere. Should this be connected to anything or is it some sort of breather pipe.

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Hi, My engine(s) are fed by a Pierburg electric EF1 pump located in the front of the car next to the spare tyre. If you search on the forum you should find other articles. I have used a Weber 30 DGF and a Solex C35PHHE10 (both twin choke) with no problem starting hot or cold as the pump primes the fuel line every time. I wonder if your problem is, if when left for a period of time, the fuel drains back from the carb somehow or if after running you experience vaporisation in the fuel line after shutting off???? Does the engine bay get very hot when running????
Ian.

Hi Ian thanks for your help, the car starts and runs fine when hot , it's only after the cars been standing for a couple of days, (when it eventually starts it seems to be running on only one cylinder for about 3 or 4 seconds I have to just tickle the accelerator pedal or it cuts out) so it must be the fuel draining away from the carb. Would you know what the spare pipe coming from the fuel tank is, finishing up in the engine bay above the height of the carb?

As per my previous comment,I think that you will find that the pipe running from the engine bay back to the fuel-tank is a fuel return pipe for the carb. The 126 had it as standard, and a number of people with big carbs fit it so that the carb isn't over-fuelled.The circulation of fuel also helps keep the fuel cool, which helps with 'hot' starts.

I agree with Tom that Fiat didn't fit an electric pump on the Abarth.... and for such a small car that isn't pumping out 100+BHP there is a lot of over engineered or over specification modifications being sold....
The std pump pumps more then enough fuel for probably any modified engine within the realms of most peoples modifications...
For example if a std car would give 50mpg, and highly tuned car gave just 30mpg then simple mathematics means that you still do not need to supply the carb with 2x the fuel....
If an engine is not being supplied enough fuel then after a while running surely it would "pink" or stop due to lack of fuel... the engine/carb cannot "suck" extra fuel needed.
Fuel supply is also aided by the height of the tank in relation to the engine, it has not got to be pumped against a huge gradient and is assisted to some degree by gravity...

Vaporisation can be an issue if the engine bay is super hot, and the engine is stopped and starting may be difficult, but if fuel vaporises to gas, then what happens when that fuel cools? is there a vacuum within the fuel line?

I commented a while back that my friends in Italy said they carry a bottle of water to spray over the pump in extreme circumstances, and Italy is considerably hotter than the UK...
I also refer back to my unusual home water problem of a strange noise... which was solved by someone telling me small bubbles were being sucked past a rubber seal into the pipework due to the weight of water... so is air entering the fuel system ?

So something I have been looking at on my cars... modern car fuel systems are more likely to be comprised of preformed tubes that are not connected using fuel or jubilee clips but male/female nut type unions that usually have a sealer on the threaded joints... as diesel owners will know air in the system is a big problem... and as such even changing the fuel filter means the system has to be re pressurised, now doing that every tie a car is parked for a few hours would be a pain...
So perhaps if a 500 is left over night there may be a small amount of air sucked into the fuel system through badly fitting pipes and clips (not helped by the extra clips/pipe to attach the unnecessary fuel filter), but as Tom has pointed out look at the height of the tank thus when an engine cools then as the fuel system is "open" (the carb is not sealed) so the fuel line would again fill up due to gravity if there was vaporisation... perhaps someone will attach some clear fuel line to the pipe as it enters the engine bay and then the height of the fuel delivered and the "level" may be determined, then given the volume of the pipe left before it reaches the pump can easily be calculated, and again see how much fuel is pumped out of the fuel pump when cranking the engine... a Carb float bowl does not have to be full for an engine to start or run... how many have fired up an engine for a few seconds with just a squeezy bottle of fuel spraying it into the carb?

The only reasons I can see for fitting an electric pump is.. adding EFI, excessive heat causing vaporisation (engine must be highly tuned and driven really hard constantly) or tinware is missing or badly fitted resulting in poor cooling... or you simply want to tidy up the engine bay, then I would be looking at locating a pump nearer the engine as there is no need to pump fuel along the main pipe (perhaps where is exits the tunnel into the engine bay) retaining the original pump as simply a filter and the "original look"..

well that's enough.. just some thoughts....

I own an Alfa 1750gtv with twin 40 dcoe carbs. I had similar problems to you with difficulty starting the car when it hadn't been used for a few days. The car would start without any problems as long as it hadn't been parked up for more than a day!

I eventually traced the problem to the accelerator pump jet washers. The jets are seated on these tiny washers and the washers seal the jet seating to prevent fuel dripping and leaking into the carb Venturi. The engine compartment of my Alfa stank of petrol and was a pig to start from cold. The washers solved the problem. I bought a set of washers from Fast Road Cars in Wales, and have provided a link here

https://fastroadcars.co.uk/store/in...uct_id=370&search=Dcoe+washers&category_id=96

They cost £2.89 for a set of 4, but you'll only need 2. Weber DCOE's have a specific starting method. Do not use the cold start device, in our climate it's more likely to cause problems. Pump the accelerator twice and operate the starter. Once the engine starts gently warm it up at a fast idle on the throttle. The Alfa has a hand throttle for this purpose. Webers are sensitive to fuel pressure as a pump pressure that's too high can cause flooding. Your mechanical pump is probably lower than 4psi so should be fine. My Alfa has a Filter King fitted to set the fuel pressure, but this would probably be overkill on your car.