Technical Want To Know

[David Britton]

For the 1st time my standard 1970 L did not start from cold but it was 35° outside the garage. Normally starts 1st time every time.

Checked previous threads and found a post with possible solution from Mr Hobbler relating to this problem. So I

1. Took spark plug out and checked spark.
Good spark and very clean plug. ?
2. Disconnected coil and fuel pipe to carburettor. Put pipe end in jar and turned engine over. No fuel in jar ! ?.
3. Pressurised fuel tank. Took tank lid off put hand over open top and put compressed air gun nozzle between fingers and pulled the trigger. You've got to love the smell of petrol !!
Fuel filled the in line filter situated just in front of pump. Reconnected all pipes and cap.

Car started as if nothing had happened. ?
Car ran got warm then turned off. Here is the problem

I could hear liquid can only be fuel draining away !
No leaks but fuel filter has very little left in it. The car did start again but am a little apprehensive to use without knowing if this is normal and what caused the initial not starting.

Thanks for any help.
David

 

[fiat500]

The car did start again but am a little apprehensive to use without knowing if this is normal

In my experience it's relatively normal for the fuel to take a few bursts of the starter before it reaches the carb when the car has been standing for a few days. I don't think the fuel drains backwards but possibly it evaporates from the bowl.

In theory, once fuel starts to flow from the tank, gravity should keep it siphoning. But the siphonage will be lost if there are any holes in the pipework or if there are any loose connections; air may get sucked in without fuel actually leaking.

If your fuel cap air intake valve isn't working properly a vacuum will be created when the engine is running which may suck fuel back once you stop.

There are small disc-valves in the pump which may also fail and which might allow fuel to draw back to the tank.

So my suggestion is that you carefully inspect the entire fuel delivery system and look for anpossible bad connections or porous or damaged pipework.

 

[the hobbler]

If the car has been left standing for a longish period of time it is not unknown for the fuel to syphon back to the tank, especially if the fuel level in the tank is low---it has happened a number of times to me (hence knowing the 'pressurise the fuel-tank' trick!). There should be no additional fuel filters in the engine bay--there is one in the top of the fuel pump and one in the top of the carb (+ the filter on the bottom of the fuel pick-upin the tank). A plastic filter on either side of the fuel pump is not wise---if for any reason it breaks, you will have fuel being sprayed over hot engine parts.

 

[David Britton]

Patinated Pete
Just got some ramps to safely check lines and connections underneath and have checked previous posts on how to access tunnel from above.

Hobbler
The car had only stood 7 days prior to it not starting. The car has stood previously 3 weeks with no issues about starting.
Just to clarify we have fuel filters
At the pick up in tank
In the fuel pump
In the carburettor?

In the Fiat workshop manual I have nothing is mentioned about fuel filters in the Service Procedure.

Mine came with a plastic filter just ahead of the pump as so many do looking on Fleabay. Never thought about it until you mentioned the fire risk it is.?
Could you please advise on what you think is the safest set up ?

What are peoples thoughts on a complete modern rubber fuel line apart from the metal part in engine bay ?
This would need to be future crap petrol proof.

Cheers

 

[the hobbler]

You are correct--just 3 filters----tank, pump and carb. As for 'ethanol-proof' fuel hose, it will say on the side of the hose that it is "ethanol compatable". I think that the actual specification is R9. For a standard carb installation, 6mm ID hose is what you require, and the use of proper 'fuel-hose' clips---they are different from 'Jubilee' clips. Any good car accesory shop should be able to supply you with both the hose and the clips OR go on-line to the "Car Builder Solutions" web-site, and ask them to send you a copy of their catalogue. It is FOC, and an absolute gold-mine.

 

[the hobbler]

Apologies, forgot your other question. The safest set-up is JUST modern fuel line from the 'through-vehicle' hose to the pump (i.e. NO filter) and just hosing from the pump up to the carb. The pump-to-carb hose should be supported by a rubber-lined bracket support bracket which fits to one of the bolts that secures the top fan-cover to the rear side-cover.

 

[gatos]

I don't want to disrespectful and don't want to divide the subject but my car is also never starting at the first time. (mr.hobbler's checklist done) also i'm always push to accelerator for start the car.

 

[Toshi 975]

The drivers handbook supplied by Fiat with a new car states the cold start procedure as full choke (fuel enrichment device) and no throttle.
Hot start full throttle and no choke.

 

[the hobbler]

The standard carburettor used on all the 500 and 126 variants (Weber IMB) has NO accelerator pump, so pumping the throttle prior to starting the engine has no gain. The correct starting proceedure with the STANDARD carb is exactly as 'Toshi' has described.