Technical Intermittent loss of power (fuel starve?) at full speed. Any ideas?

[thisisburdett]

Hello all, Happy belated New Year to you all.

A little more info on the title. When driving flat out (perhaps that’s the cause?!) the engine seems to choke, the revs drop off and then I lift my foot off the gas and feather it back on and we’re ok again.

It happens here and there, but always when going full pelt, usually when keeping up with modern traffic on the odd dual carriageway.

Perhaps I need to clear the fuel lines, but thought I’d run it by you lot first to see if anyone has experienced something similar and has a solution? Thanks in advance!!

Ps. I just swapped out the plugs and it’s still occurring.

Thanks again!

 

[the hobbler]

Hello all, Happy belated New Year to you all.

A little more info on the title. When driving flat out (perhaps that’s the cause?!) the engine seems to choke, the revs drop off and then I lift my foot off the gas and feather it back on and we’re ok again.

It happens here and there, but always when going full pelt, usually when keeping up with modern traffic on the odd dual carriageway.

Perhaps I need to clear the fuel lines, but thought I’d run it by you lot first to see if anyone has experienced something similar and has a solution? Thanks in advance!!

Ps. I just swapped out the plugs and it’s still occurring.

Thanks again!

The fact that lifting off the accelerator reduces the problem, and that it only happens when you are driving 'rapidly!' would leave me to think that the problem is a brief lack of fuel. Check your filters---you should only have (and need) 3; fuel-tank pick-up, top of fuel-pump and top of carb. Do you have a 'non-return' valve in your fuel system? I ask this because the Fiat fuel-pumps are 'pushers' and not 'pullers'. A quick check of the float level in the carb would also be a wise move---if it is too high, it will shut of the fuel supply too soon

 

[bugsymike]

The fact that lifting off the accelerator reduces the problem, and that it only happens when you are driving 'rapidly!' would leave me to think that the problem is a brief lack of fuel. Check your filters---you should only have (and need) 3; fuel-tank pick-up, top of fuel-pump and top of carb. Do you have a 'non-return' valve in your fuel system? I ask this because the Fiat fuel-pumps are 'pushers' and not 'pullers'. A quick check of the float level in the carb would also be a wise move---if it is too high, it will shut of the fuel supply too soon

As Hobbler says, also check main jet in carb and blocked vent or non standard fuel cap.
Highly unlikely but a non standard air filter or carb can cause icing up even on warm days, but by the time the engine is inspected it has all disappeared/melted.

 

[thisisburdett]

The fact that lifting off the accelerator reduces the problem, and that it only happens when you are driving 'rapidly!' would leave me to think that the problem is a brief lack of fuel. Check your filters---you should only have (and need) 3; fuel-tank pick-up, top of fuel-pump and top of carb. Do you have a 'non-return' valve in your fuel system? I ask this because the Fiat fuel-pumps are 'pushers' and not 'pullers'. A quick check of the float level in the carb would also be a wise move---if it is too high, it will shut of the fuel supply too soon

That’s very helpful! Thanks for the speedy reply and pointers. Will run through them once I get a minute.

Thanks again!!!

Enjoy the weekend.

 

[RalphM]

Fuel tank filler cap breather?

 

[fiat500]

If all the above, more obvious solutions fail, check that the fuel-pump is not coming loose.

 

[timmycm850]

I would imagine a vacuum being created in the fuel tank making it difficult for the fuel pump to work properly.

Try running the car on your regular test route but with your fuel filler cap undone by about 1/2 turn, tape one run of tape over the cap to stop it shaking loose while you test.

Our gamine did this after 20 minutes or so but entirely cut out until the filler cap was removed an refitted. To stop it we made sure we had a vented fuel filler cap and fitted an electric pump up the front by the tank, it is useful when the car stands for long periods so the electric pump can prime the system.

Tim

 

[bugsymike]

On a different note just curious, but at the beginning of your thread you describe driving" flat out".
I confess the Fiat 500 I owned was a red 1966 reg. OTY??? around 1978, I drove it with my foot on the floor for around 250 miles with my first wife, fully loaded with all we needed for a weeks holiday on a canal barge. What impressed me at the time was 55MPG @ 55MPH on the speedo most of the way, though we were a bit deaf when we got there.
Note, the car was fully loaded, not my first wife , although after the divorce she got the Fiat 500, a 1971 Alfa Romeo 1750 GTV and half the house, not bad for 18 months marriage

 

[Bleeding Knuckles]

Hi TIB, further to Peters comment maybe you have a tired fuel pump that is simply not keeping up with the demands of the carb???
Ian.

 

[RalphM]

Sister in law had a 500 and then a later 600 both were driven flat out over
long distances always 2 up but often 4 up she used to row the poor beast
along on the gear leaver had them for years.

 

[the hobbler]

Sister in law had a 500 and then a later 600 both were driven flat out over
long distances always 2 up but often 4 up she used to row the poor beast
along on the gear leaver had them for years.

An Alfa 1750GTV!----I would REALLY have cried having to give that up!

 

[bugsymike]

An Alfa 1750GTV!----I would REALLY have cried having to give that up!

1971 Bertone body, the one before the wedge shaped later ones, whenever you see them nowadays they are doing classic racing and valued well in access of £10k, she part exchanged it at a Leyland dealer for a Morris Marina!!! I think the Reg. was something like J777*** or ***777J
I just loved that car, the sound and the look.