General Engine stalling when hot

[lazylobster]

Hi all, a hot day yesterday around 25c (hot for UK that is) and took madam for a long drive. When oil temp starts to get over 80c and car not moving, sat in traffic etc, then the engine starts to die and I have to give her a rev to keep her going. :bang:


The thermo flap is fully open, engine idle is 1000rpm. When moving the oil temp drops down to 60 ish. And no problems with lack of power, missing, cutting out or anything else.


Does not seem to be ignition but maybe more fuel stavation. Has a new fuel pump fitted not so longago. Again, been running great over long distances no problem. Just seems to be when the engine gets very hot and sat waiting to move off.


I do get a slight smell of petrol in the cabin so wonder if there is a slight leak in the pipe running through the cabin. No sign / smell around the fuel tank. How can I check this, I think there is a connect from the rubber fuel tank hose to the copper fuel line?


Your help please!

Thanks
Rob

 

[JumpJet]

I've been having the same issues lately. Little Martina had been running like a top, but as temps have reached 36C, once she has fully warmed up, every stop seems a challenge to keep her running. I've found that using the choke lever a bit helps, but can't identify any solid cause.

 

[lazylobster]

I've been having the same issues lately. Little Martina had been running like a top, but as temps have reached 36C, once she has fully warmed up, every stop seems a challenge to keep her running. I've found that using the choke lever a bit helps, but can't identify any solid cause.

Seems to be another "feature" of 500 ownership. I've posted the same question onto 500forum.it web site. As a big community of Italian 500 owners there. A response so far (using google translation) is :

"It could be the seal of the needle valve or the level a little high ... the fuel pump is new, perhaps the pressure is a little high, add a gasket under the pump to space it out .. with this operation the delivery pressure is reduced .

Walking on the road, the fuel consumption compensates for the extra quantity that enters the tank .. when we are forced to slow down in traffic, the problems come .. even the carburetor float that has become heavier creates the same defect."


I'm not sure (as I'm no expert) why a high pressure fuel pump would cause the engine to stall when on idle. Also, I'm not sure what the last paragraph means. Maybe some of the more engineering literate people could chip in ?

Cheers
Rob

 

[lazylobster]

Another response from the Italians below and this one kinda makes sense as it felt more like a lack of fuel getting to the engine. Once the engine was rev'ed, then ok and ok when moving:


I meant gasoline pump, when it gets very hot it stops pumping gasoline.

?????

 

[Franko500]

I read a similar question on a FB site.
Italians suggest chuck a bottle of water on the pump to cool it down.


I still haven't resolved my running problems. Starts fine, runs fine. I let it get really hot on my driveway then turn it off. Starts almost every time.


But if I go for a drive and it gets hot and I turn it off it wont start until it cools.


Seriously thinking of fitting a SU pump? I still have my inline filter in place and it indicates to me fuel starvation. And yet I also get the horrid fuel in the drip tray of the carb. Where does that come from?

 

[lazylobster]

I read a similar question on a FB site.
Italians suggest chuck a bottle of water on the pump to cool it down.


I still haven't resolved my running problems. Starts fine, runs fine. I let it get really hot on my driveway then turn it off. Starts almost every time.


But if I go for a drive and it gets hot and I turn it off it wont start until it cools.


Seriously thinking of fitting a SU pump? I still have my inline filter in place and it indicates to me fuel starvation. And yet I also get the horrid fuel in the drip tray of the carb. Where does that come from?

Yes, I’ve seen the odd post of a water bottle over the fuel pump. Did wonder why but now its clear. Took madam for a drive today. Got her up in the 80’s no issues. Left her on the drive and faultless. But, a lot cooler today and i had just filled the tank up. So a big coolbag of fuel up front.

Guess ill have to wait until the next hot day and take a bottle of water with me

If this is the cause, then they must be a fix apart from putting in an electric pump

R

 

[fiat500]

I think one of those Italian responses is meaning that on tickover or over-run, a mechanical pump may supply more fuel at a pressure that the carb needle valve can't hold back. This will flood the engine and/or cause leakage/fumes.

In the same situation, if the pump is correctly set to idle when fuel is not being consumed, the unused fuel sits in the pipes etc. and vaporises.

As the larger capacity engines were designed with a bypass to return surplus fuel, the pump may have been designed to provide excess fuel delivery. A solution may be to provide a proper fuel return, which is a satisfying but not a straightforward job to do correctly.

 

[Vitesse]

I read a similar question on a FB site.
Italians suggest chuck a bottle of water on the pump to cool it down.


I still haven't resolved my running problems. Starts fine, runs fine. I let it get really hot on my driveway then turn it off. Starts almost every time.


But if I go for a drive and it gets hot and I turn it off it wont start until it cools.


Seriously thinking of fitting a SU pump? I still have my inline filter in place and it indicates to me fuel starvation. And yet I also get the horrid fuel in the drip tray of the carb. Where does that come from?

Did you blank off your fuel return on the IMB28 carb Sean or return it to a T piece? I have a video of my 650 engine where I extended the fuel line using some clear pipe between the pump and carb as a bit of an experiment. The flow of fuel through the pipe is sporadic to say the least, there are times when it looks like no fuel is flowing, it comes through in big blobs or there is loads of air bubbles. But the engine is ticking over sweet as a nut.

I have hot start problems in the past and it has always the tappets, never seen an issue on my 500 in the past, what is nearly 30 years of owning it, with fuel starvation. Also the fuel filters are known to cause issues with restricting fuel flow.

 

[the hobbler]

If you have a 'return' pipe coming from your carb, As 'Vitesse'has mentioned it is not a difficult job to put a METAL 'T' piece into the fuel line before the fuel pump and taking a fuel-pipe from the return outlet on the carb down to the 'T' piece--it just allows any surplus fuel to circulate. The fuel pump is operated by an actuating rod through from the camshaft. This rod should extend out past the space AND the gaskets 1 to 1.5mm at the point is IN the furthest (or, if you want to look at another way) out the LEAST.

 

[schwenkenheimer]

Has anyone had a similar issue when trying to downshift? I was driving at about 80-90 KPH for about 30 minutes and went to downshift on the off ramp when the engine just cut out on me and would not start for about 30 minutes I assume until the engine cooled down. It has done that to me 4 times to the point where Luigi has been put in the garage for a while until I did some research into possible causes.

 

[DimitriL]

Hi all, a hot day yesterday around 25c (hot for UK that is) and took madam for a long drive. When oil temp starts to get over 80c and car not moving, sat in traffic etc, then the engine starts to die and I have to give her a rev to keep her going. :bang:


The thermo flap is fully open, engine idle is 1000rpm. When moving the oil temp drops down to 60 ish. And no problems with lack of power, missing, cutting out or anything else.


Does not seem to be ignition but maybe more fuel stavation. Has a new fuel pump fitted not so longago. Again, been running great over long distances no problem. Just seems to be when the engine gets very hot and sat waiting to move off.


I do get a slight smell of petrol in the cabin so wonder if there is a slight leak in the pipe running through the cabin. No sign / smell around the fuel tank. How can I check this, I think there is a connect from the rubber fuel tank hose to the copper fuel line?


Your help please!

Thanks
Rob

In the beginning I also had fuel smell in the cabin, like a dog I sniffed from front to back, I suspected the fuel tank as well, but no... It was from the back, the carburetor was leaking, I couldn't easily see from where, but it was the brass fuel inlet pipe that was loose, I found this because I turned the rubber fuel hose coming from the fuel pump, and noticed that it turned very easily at the top by the fuel inlet of the carb. I have a post on this. I took the carb out, was able to pull out that fuel inlet pipe very easily, I sanded it and the body of the car and JB Welded it. That got it fixed. Also, I removed the fuel filter on top of the fuel pump, and placed the fuel filter by the gas tank in the front. I didn't like the idea that this mass of fuel gets hot. I always saw airbubbles when the engine was hot. Also, did you check of the thick hot air hose is well clamped down on top and bottom? Also, do your spark plugs have rubber caps? Cheers.

 

[Franko500]

Did you blank off your fuel return on the IMB28 carb Sean or return it to a T piece? I have a video of my 650 engine where I extended the fuel line using some clear pipe between the pump and carb as a bit of an experiment. The flow of fuel through the pipe is sporadic to say the least, there are times when it looks like no fuel is flowing, it comes through in big blobs or there is loads of air bubbles. But the engine is ticking over sweet as a nut.

I have hot start problems in the past and it has always the tappets, never seen an issue on my 500 in the past, what is nearly 30 years of owning it, with fuel starvation. Also the fuel filters are known to cause issues with restricting fuel flow.

Hi Tony, yes I blocked it off.
In theory the pump should not provide too much fuel as A. the float & valve should shut off when full. B. The diaphragm in the pump is designed to stay in the down position when the bowl is full and thus causing the fuel pump to not actual work.


I have reset my valve clearances, changed my fuel pipe front to back. All seems to run ok. I think my problem was the battery although charged, was not charged enough to start a warm engine and run out of umf before enough fuel got through. Too much sitting around.
With a long trickle charge it seems to start fine. Well not as fine as I would like when warm. But I think that is a fuel issue.


I might try Tom's method with the fuel return.

 

[Toshi 975]

The value and effectiveness of the fuel return circuit was always a mystery to me so on one of the more recent engine rebuilds I did when I bench tested the engine I also rigged up a separate jam jar to catch the return flow. I was surprised at how quickly a 1 pint jar filled up. It was certainly returning more fuel than the engine was using while running.

 

[Vitesse]

I might try Tom's method with the fuel return.

It’s what I did as well. As Dave says there is an amazing amount of fuel returned out the return line pipe on the carb, it has to help with cooling the fuel if it is constantly moving and circulating around.

Peter’s method of running an return line all the way to the tank is probably the ultimate solution as it will allow even more cooling. There has to be a reason why Fiat added the return line to the tank and the only logical reason is to assist with cooling the fuel?

 

[DimitriL]

I didn't know about this return fuel line. My 500F does not have it.

 

[the hobbler]

To the best of my knowledge, non of the 500s had a fuel-return line (the 500R, although it used a 126 engine, had a small carb fitted to curb performance) and the 24 and 26IMB carbs only had an 'in' to the carb. The 28IMB used on the 126 engines had both an 'in' and 'out' fuel-pipe to the top cover. The capacity of a 126 fuel-pump is 0.73 pints per minute (5.5 imp gallons per hour). As you can see, no matter HOW fast you drive 500, no matter what engine is fitted, there is absolutely no way you will be able to use that amount of fuel---hence the return.

 

[fiat500]

I didn't know about this return fuel line. My 500F does not have it.

It is not fitted to the 500 but it was on the 126 and on many other cars of the era and it is a feature of modern fuel systems.

In addition to cycling the fuel properly for cooling, which the use of a "T"-piece does not do, a fuel return ensures that the supply pressure of the fuel at the inlet to the carb remains constant and in surplus. This avoids pressurising the float-valve in the carb which otherwise initially occurs when there is an excess supply when idling or going downhill. Consequently, the pump is able to work at a constant rate and the mechanism avoids a regular stop/start scenario.

Since plumbing in a return system there are no leaks of fuel around the carb which means that there are no petrol fumes in the passenger compartment coming from the engine. There has never been a starting or running problem which could be blamed on vaporised fuel and the car starts immediately..hot or cold.

There is a lot of surplus fuel being cycled at tickover, which I can hear returning to the tank. I don't consider this modification to be essential but it has many merits.

 

[Labman]

Could be your coil getting too hot and acting up. I isolated my issue to a new coil I had put in. Engine would not start when hot after it stalled. I blew air from a leaf blower on the coil for few minutes and then it started. I had an old coil and swapped it out, and added a heat shield to block heat from the muffler and haven't had an issue since.