Overheating...

[mintex]

Its not an inlet or outlet valve set to tight is it and as it warms its not closing properly?
Seems like you've covered almost everything so far?

Ive had a very very similar problem with a motorbike and the turned out to be the carb float heights to high and it was flooding but only slightly and the excess fuel was making its way into the oil causing it to run rich as it was sucking the fumes from the petrol back into the engine by the breather.

It would start very easy when cold with little or no choke but as it warmed it would choke itself on the over rich fumes and slowly die until it cooled down then it would fire up and do it all over again.

I'm not familiar with the air cooled setup so dont know it this is possible on the fiat?
.

 

[DeVilleChris]

That does sound possible, it smells very rich.

[dadandlad]

Hi Gary
Once it cuts out will the engine turn over on the starter, still plenty of power in the battery ?
I have my suspicions the dynamo isn't putting out enough power to keep it running

I can pop down for a couple of hours one evening next week and have another look if you want

Don't get disheartened we will sort it 

[DeVilleChris]

I have a suspicion its fuel related. new battery with lots of charge 

[1973/126]

 Chris have you checked for leaks around the carb? Try to spray some carb cleaner round it and see what happens.
 These carbs and spacers under them tend to warp from the heat, so need to check everything to make sure it`s sealed properly.
 I also had a similar problem recently on a 500 and it turned out to be a worn out butterfly spindle. It just wouldn`t idle properly and would eventually just conk out.

[DeVilleChris]

I've tried round the carb yeah, even put new gaskets on it. No air leaks that I can find

[1973/126]

 Try it with a different carb from a good running car. At least you can then eliminate things.

[DeVilleChris]

Yeah I'll take a carb I have down that I know works. Thanks!

[alastairq]

Re- inlet air leaks? 

Might be an idea to smear some 'seam sealer' on to  gaskets etc?  Air  leaks tend to be so small, that a lot of spray liquids [wd40, for example] are just too thick in consistency to find them [best use easy start for finding leaks?]  Had this issue on another of my cars last year, when using an old-school rolling road to set it up after reconstruction.....Old-school tuner suggested seam sealer on gaskets as a good way of sealing properly....it worked, too.

Not having read through the whole thread, I'd try bypassing the fuel pump with an electric one?

[Bar Vitelli]

Thanks, Mark...Chris is popping back next Friday so will hopefully get sorted.  We fitted a new battery so don't think it's that. To be honest, there's not much left to try so we can't be far away.

PS

I've not forgot the curry night, just got busy with work, will sort soon and will be great to meet up again. Likely to be turkey curry... 

[Darrell]

Hi, not sure if you guys have checked this but the mysterious cutting out could be that pesky rod that pushes the fuel pump. As the crankcase heats up the problem gets worse as now the rod is even shorter. It cools a bit then starts pumping again.
It runs strait off the cam and wears with time, could explain overheating too as the poor thing would be gasping for fuel, a it like Pete when he arrives at Retro rides looking for a beer. Might have missed that if you mentioned it.

I've pulled my manual pump off, installed a pressure regulator and running an electric pump, Installed an extra breather where the old pump was better breathing and more constant fuels pressure on the needle and seat is the theory.

It's just a thought.

You do know what Fiat means don't you? Fix It Again Tomorrow 

But seriously when you get them running well they can be very reliable and cover some impressive distances.

In my experience there are two major reasons for overheating, Ignition timing or running lean.

It may sound very simple but you have to simplify it or it turns into a witch hunt. Thermostat in my opinion is extra weight on the air cooled and BIS.
Oil coolers help imensly if you start pushing for higher performance and the old boot lid opener on the air cooled helps hugely too. I know oil etc is a factor but then if it overheats it destroys the oil.

I had an electronic ignition thing that had curves you set with toggle switches. It now lives in a box in the shed, I think the guy who made it must have had a bad day or something because no matter what I did with it the car overheated. The simple one that goes where your points were is my preference.

Not sure if that rambling is of any use, good luck with that one

[Darrell]

Just one more thing, please don t drive it far like that.
Overheating results in cracking of the head between the two valves. 

[Bar Vitelli]

Thanks, Darrell, I'm psyching myself up to have another go this weekend. 

[Yoshimisumi]

Just read through all this as I'm having strange cutting out issues now and occurring over progressively shorter distances! Is the switch to an electric fuel pump with regulator easy enough? Sounds a no brainier.


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[Darrell]

You could just remove the rod that pushes the pump and by-pass the mechanical pump.
You could just push the fuel through the mechanical pump not sure how well that would work but it should work as there is just valves in the pump.

Or you could make a blanking plate and remove the mechanical pump. I did this and used the plate you can buy which has a breather pipe outlet attached. It just helps the lower crank breathe.