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Technical 1972 500L cutting out problems

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Technical 1972 500L cutting out problems

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topolino2000

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I have a 1972 500 L which has covered a genuine 28000 miles.
It starts ok every time but after about 15-20 minutes it starts to loose power gradually and eventually dies.
It will then not start for about 10 mins until it has cooled down a bit.
I have renewed points, condenser, coil, HT leads, dist cap, rotor arm, needle valve, checked float height, substituted fuel pump for electric one in case pushrod had worn, reset valve clearances to 126 spec (wider) in case they were closing up, removed and cleaned fuel tank and renewed sender unit/pickup, renewed all relevant fuel lines, checked engine thermostat, tried different heat ranges of spark plug etc etc.
Have checked valve clearances within a minute of it cutting out and they are fine. Am running out of thoughts now. Any idea's?
 
Clearly something breaking down under heat.

At first I would have gone for the coil, as I had a very similar thing happen, but as you have already changed that..... :confused:

One thing does spring to mind.... I am wondering whether the face of the flange on your carburettor may be distorting when it gets hot, allowing an air leak and consequent fuel starvation?

What colour are the plugs - normal or white?

Is this something that happened suddenly?
 
oopsadaisy said:
Clearly something breaking down under heat.

At first I would have gone for the coil, as I had a very similar thing happen, but as you have already changed that..... :confused:

One thing does spring to mind.... I am wondering whether the face of the flange on your carburettor may be distorting when it gets hot, allowing an air leak and consequent fuel starvation?

What colour are the plugs - normal or white?

Is this something that happened suddenly?
Click to expand...
.
Have checked carb flange and also checked spacer block between head and carb for hairline cracks (it's ok). Many years ago 500's and early 126's had problems with this spacer block.
Also fitted new spacer block gaskets.
Plugs are fine (light brown).
Have also removed rocker cover within 60 seconds of cutting out and checked valve clearances. all ok. Pushrod ball ends are ok (have occasionally seen them worn through).
As I am convinced it is heat related, I have even held thermostat open at max position but makes no difference. There isn't much more to try now. (It's a standard 499cc engine).
 
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How very annoying! :(

From what you are describing, all my gut instincts are saying 'ignition problem' in view of the breakdown when the engine is hot, but will start when it cools off.

Especially given the colour of the plugs that indicates all is well in the fiel department.

My only thought now is that it could be something you have already changed that is still not right.

For example, I once fitted a pair of brand new Fiat spark plugs to ours (bought off Ebay) and had all kinds of problems. Very similar symptoms actually - it would run fine for 10 - 15 minutes, then power would start to become intermittent, followed by the engine dying totally - usually just as we entered a really busy junction........ :cry:

I did the same as you and checked everything, plug gaps, colour was OK, checked points gap, etc. etc. then after it had cooled for ten minutes or so, away it went again!

I thought, can't be the plugs - they are brand new - but guess what - it was! Put a new set of NGK's in, and it was absolutely fine!

So, you may still have a dodgy part that you have already changed - main culprits that spring to mind are condenser and coil.

Is the coil on the right hand side of the engine bay near the exhaust pipes? Some owners I have met firmly believe that the coil 'cooks' in this location due to it's proximity to the exhuast.

Where are you geographically?

Could you get together with a fellow owner and maybe swap bits and see what happens?

One thing I DID invest in and have not regretted it despite the financial outlay, is a 123 Electronic Ignition Unit, which eliminates all potential problems with the original breaker / distributor set up once and for all!
 
oopsadaisy said:
How very annoying! :(





Thanks for your thoughts. I have tried 3 different coils (all proper 500 coils, not just a 12v unballasted mini coil etc) and the coil on the vehicle now is brand new. I still tend towards a fuel problem or air leak as even when it cuts out there is still a strong spark.
Have also tried three sets of plugs, the last two sets being different heat ranges of NGK.
I have just ordered a bakolite carb spacer block and gaskets from Chet because i am not totally convinced about the one i have although it looks ok. (thirtyish years ago when 500's were more common in the UK these used to give problems as i recall. Carb flange has been checked and is true. Everything is solveable, it's just a matter of elimination.
Click to expand...
 
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oopsadaisy, do these syptoms ring any bells - refering to your extended journey to Autoitalia?? All sounds very familiar:confused: am I right in thinking that the electronic ignition cured it ????
 
Panda Van said:
oopsadaisy, do these syptoms ring any bells - refering to your extended journey to Autoitalia?? All sounds very familiar:confused: am I right in thinking that the electronic ignition cured it ????
Click to expand...

One thing I DID invest in and have not regretted it despite the financial outlay, is a 123 Electronic Ignition Unit, which eliminates all potential problems with the original breaker / distributor set up once and for all!
Click to expand...

It did - but I also changed the plugs, coil and HT leads......

Still highly recommend the 123 unit though, and no, I'm not on commission!
 
Fitted new carb spacer block and gaskets.
Had base of carb machined flat and checked on datum block.
Guess what.........now runs and idles perfectly (for hours)
BUT............when you turn engine off and try to start again.....no start.
Will crank over but will not fire. Spark, fuel, compressions all there but no start.
Leave it 10 minutes and hey presto, bursts into life.
Looks like i had two seperate problems, one of which i have cured.
Mmmmmmm......back to the drawing board.
 
Just a thought, I had experience a number of years ago with a similar problem not on a fiat though. it turned out that the tank vent was blocked so the fuel pump was creating a vacuum in the fuel tank to the point that it could no longer draw fuel. Try (only with very little fuel in the tank) carefully driving with the fuel cap off or loose and see what happens.
 
Actually just read a similar thread on 'another' forum........... :rolleyes:

The poster had similar problems which he eventually traced to the fact that he had fitted new flexible fuel hoses, and pushing them on over the ends of the metal ones had resulted in a small 'flap' of rubber being peeled back, which then intermittently blocked the fuel line........

Worth a look?
 
oopsadaisy said:
Just a silly thought........ ignition switch?

High resistance = heat = connection breaking when you turn the igntion off........ switch cools, connection re-makes.........

Just a thought.......... :bang:
Click to expand...
Yes, i understand what you are saying but good strong spark when cranking (well, good spark showing at in line plug tester but who knows what at electrode when under compression). Pity they dont make glass heads for 500's, would certainly prove if i have a spark, fuel etc.
 
gazzol said:
Just a thought, I had experience a number of years ago with a similar problem not on a fiat though. it turned out that the tank vent was blocked so the fuel pump was creating a vacuum in the fuel tank to the point that it could no longer draw fuel. Try (only with very little fuel in the tank) carefully driving with the fuel cap off or loose and see what happens.
Click to expand...
.
Well, we both seem to be thinking along the same lines (obvious things exhausted so try the wierd) but yes, i have tried with cap off and no different. Keep thinking though and we will crack this.......one day.
(Next thing i am going to try is running it directly from a fuel can on both current SU pump and reverting back to mechanical pump.
One other thing that i have known in past is if the starter motor heats up, it can draw too much current and not leave enough for the spark.
Unlikely but a possibility.
 
It's not something stupid like the wire to the condenser arcing out occasionally under the cap when the advance alters is it?
 
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