General Fuel Starvation

[Tin Tin]

I do not know why, but recently there have been a number of posts relating to fuel starvation.

It happened to me recently after the winter lay-up. No fuel to the fuel pump and no start despite plenty of fuel in the tank and the fuel tank filler cap venting properly.

Once I removed the fuel pipe from its pump connection and sucked through the fuel, hey presto the engine started.

I still have no idea what caused the fuel starvation:
· - Blockage
· - Vacuum
· - Pump failure

But by fitting an electric fuel pump next to the tank, leaving the mechanical pump in place and all now is fine.

I am really curious to know why there seems to be so many cases of fuel starvation.


Peter

 

[AndrewHarvey]

I guess all the fuel in the line would of evaporated during its lay up
Maybe the pump struggles to self prime - being so far from the tank??

 

[fiat500]

There are many discussions on the internet which seem to point to the fact that modern fuel is more volatile than it used to be.
I have had one car-stopping occurrence which was definitely caused by fuel vaporisation inside the pipe and that was one of my cheeky days using super-unleaded. The car regularly has a jittery moment, which I have become used to, for a few seconds after starting when temporarily stopped with a very hot engine which I put down to vaporisation, possibly in the carb.
Our cars have the disadvantage (for this problem) that the very hot air from the engine is directed over a significant length of the fuel pipe when the heater is being used. I have wondered if this might contribute to fuel vaporisation. Obviously it is less likely that the heater will be being used on the sort of hot day (rarely experienced by me) when vaporisation is likely to happen, which is where my theory falls down.
I have another theory that the short length of steel pipe that carries the fuel around the engine-bay, dispensed with by many restorers, possibly acts as a primitive cooler to dissipate some of that heat.

I have seen it said that the fuel pump is a "pusher" not a "puller". If I understand that correctly it is because there is usually a reliable head of fuel at the inlet to the pump because the tank is higher than the engine and siphonage maintains a flow. When there is a interruption in this flow caused by fuel evaporating back to the tank then there is possibly only a very small amount of depressurisation inside the pipe, caused by the pump, to start the flow going again?

 

[Franko500]

Very well put Peter.
Fiat also added an additional flap on top of the 126 fan housing that when opened will blow air onto the carb and therefore help reduce vaporisation.
I have yet to try it out to see if it works. They also fitted a solenoid valve on the later SIA carb to shut off the flow of fuel in the carb to prevent run on and I believe to maintain a higher amount of fuel left in the bowl for restarting. Tony kindly sent me his working one, of which I did try but for some reason I couldn't get the engine to run right. After I noticed its a different jet size so have yet to experiment with that as well.

 

[AndrewHarvey]

Whilst plumbing my new pump and filter I removed the sender unit.
The outlet has a filter on the end and mine was completely clogged up.
I blew it out with compressed air and took a closer look.
It is a brass contruction and fell apart when I touched it.
I removed it as I am running a Malapassi filter regulator after the pump - and a micro-fine filter before the carb.
This will effect fuel availability......

 

[Franko500]

My saga continues today!
Franko has been running really well recently with no starting issues hot or cold. He also hasn't skipped a beat.
Today I drove about 5 miles to Tescos to fill up as I was just below 1/4 tank.
Filled the tank to about 7/8's thinking make sure there is some space in the tank after last time. He started straight away, drove over to the store and parked up and then went in for about 10 minutes. Came out, started fine, drove about 7 miles to the mother in laws. turned engine off.
5 minutes later it wouldn't start. There was spark and fuel in the filter. I didn't take off the pipe to check flow but I have a feeling there wasn't any flow. Checked points & spark, then took off fuel cap.
Engine started.
The cap is definitely breathing okay as the little valve is free.


Maybe new cap or don't go to the mother in laws?

 

[fiat500]

Researching the other main air-cooled car, of whom I shall not utter the name; as expected, I see that they have the same problem. One simple, part-solution that I had already thought might work, is to wrap the fuel pipe in the engine bay in foil-tape. There is something you can get for lagging domestic water pipes to keep heat in which would work in reverse for the fuel.

 

[the hobbler]

One of my reasons for utilising the fuel return facility of the Weber 28IMB carb is that by cycling the fuel round, its own motion tends to keep it cooler.
The question regarding visiting 'the mother-in-law' is surely outwith the remit of this forum--and well below the belt!!

 

[AndrewHarvey]

Have you checked the filter in the sender as I mentioned last week?

 

[Franko500]

The tank was fully stripped, flushed, painted, flushed again and the sender stripped, cleaned and the filter was all intact.
I have a feeling it must be due to a vapour lock in the tank after filling as I have started it 5 times since and no issues!
Ps. Took the mother in law home in my other car, so I can't be for sure if it was just a case of Franko not liking her!

 

[Vitesse]

I wouldn't say it was normal behaviour but it is very common the hot starting problem. It's probably one of the most frustrating issues as the car seems to run fine and start from cold ok.

I tend to find when I get it there is definitely a time element to it. If you stop, fill up at the petrol station and it takes say 5mins then my 500 will start perfectly OK. If I drive somewhere switch off and leave it between 10-15 minutes it can be a pain trying to restart. But I find if you just crank it over with no throttle and wait for it fire once, then give it a little quick squeeze on the pedal, it will continue to fire and then you just fettle the pedal up and down a few times and it will catch and start ok. I think it has become second nature now as I have had to do it so often. In the past when It had suffered it badly I found it helps to leave the engine lid open.

My understanding is that once the engine is turned off, because of the lack of cooling provided by the fan and the normal flow of air from driving. The engine temperature will continue to rise for a period of time and that is when vaporisation starts to happen, initially it doesn't occur because the fuel in the lines is cool. It's one of the reasons why I put the thermo tape on my exhaust to see if I could keep the engine bay temperature down a bit.

 

[AndrewHarvey]

Does this situation improve when the fuel pump is changed for a front mounted electric one?
The fuel delivery would be pushed not pulled...just a thought.....

 

[Vitesse]

I have always found if I have hot starting problems in the past that adjusting the tappets seems to cure it. It definitely made a considerable improvement put it that way.

I found this on the Proietti website. I have been to their place a number of times in the past and they know their stuff, so it could be worth a try.

http://www.fiat500.cc/store/ViewArticle.asp?idProduct=303

 

[fiat500]

I have always found if I have hot starting problems in the past that adjusting the tappets seems to cure it. It definitely made a considerable improvement put it that way.

I found this on the Proietti website. I have been to their place a number of times in the past and they know their stuff, so it could be worth a try.

http://www.fiat500.cc/store/ViewArticle.asp?idProduct=303

I think I've said previously that I've had the same outcome as Tony.
I've seen that Proetti instruction before and disagree with it. What's a "hot" engine? Very hot? Fairly hot? At least adjusting cold, ie. has not been running for several hours, (as all the manuals describe), should be reasonably consistent.
If you really could adjust the valves when the engine was as hot as it can get, I think you could adjust the tappets to have almost zero clearance, as the idea of having a cold clearance is to allow for the expansion of all parts when at working temperature; so that the gap is then virtually closed-up.
The Proetti way will give plenty of clearance cold, which will reduce the chances of a poor hot-start, but I think it might lead to a clattery and less efficient engine.
At best, for all the trouble, I doubt it has any better an outcome than just keeping things simple.
The main thing that I'm picking-up with these engines is that it will pay you to check the the valve clearances regularly.

 

[the hobbler]

I totally agree with Peter--tappets should be adjusted (as per the 'book of words') COLD. I did my time on Mercedes-Benz--and their instructions were to always adjust tappets COLD. Their reasoning was, as Peter asked, "how hot is hot?", whereas if you left the engine overnight, it was as cold as it was going to get in the morning. I also agree with Peter, doing tappets hot can lead to a very clattery engine when it is cold---as well as you risking burning tender parts of your anatomy, because not only the tappets are hot!

 

[Bigvtwin996]

This Hot start problem has only happened to me once (N fitted with std 650 engine) I thought I'd best offer some info I got from my Italian friends (Fiat 500 Club of Turin)...
Firstly they don't put the fuel filter in the engine bay, they locate it just after the tank, as in the engine bay it provides a larger surface area to heat up the fuel, up front it does not get as hot.
secondly they are of the opinion it is not the fuel pipe that allows the fuel to vaporise, but infact the actual fuel pump body.
Their solution is to carry a cloth and bottle of water and use these to cool the pump body down should starting become a problem.
I did wonder about trying a can of "Freeze Spray" (mainly used for sports injuries) but not sure how flamable it is...