Technical Occasional low revs

[Bubins]

Hello,

I've had problems with my 500 where as I'm driving the car will suddenly start to judder and lose power. As it might if it were about to stall. I had it taken to a garage where they cleaned the carb and the problem seemed to be fixed but it has now started again. This time it only happens very occasionally and hasn't resulted in a total breakdown as it did before.

It happened once when I was driving slowly so I stopped, put the car in neutral, and tried revving the engine. What I found was that even with the accelerator peddle fully depressed the revs stayed reasonably low. After releasing and depressing the pedal again (not sure how many times I did this) the revs went back to normal.

Something is happening that is causing the revs to sometimes stay low, which causes the car to judder and stop if it happens when I'm driving. Any idea what might be causing this?

A mechanic that attended during the breakdown suspected there was an overfuelling issue (he said he smelt fuel on the spark plugs). I'm not sure if this is connected. Perhaps an issue stopping fuel going to the right place is sometimes causing the car to have issues revving as high as it should.

Any advice very appreciated.

 

[bugsymike]

Hello,

I've had problems with my 500 where as I'm driving the car will suddenly start to judder and lose power. As it might if it were about to stall. I had it taken to a garage where they cleaned the carb and the problem seemed to be fixed but it has now started again. This time it only happens very occasionally and hasn't resulted in a total breakdown as it did before.

It happened once when I was driving slowly so I stopped, put the car in neutral, and tried revving the engine. What I found was that even with the accelerator peddle fully depressed the revs stayed reasonably low. After releasing and depressing the pedal again (not sure how many times I did this) the revs went back to normal.

Something is happening that is causing the revs to sometimes stay low, which causes the car to judder and stop if it happens when I'm driving. Any idea what might be causing this?

A mechanic that attended during the breakdown suspected there was an overfuelling issue (he said he smelt fuel on the spark plugs). I'm not sure if this is connected. Perhaps an issue stopping fuel going to the right place is sometimes causing the car to have issues revving as high as it should.

Any advice very appreciated.

When original mechanic cleaned carb, did he say what he cleaned out of carb? As in dirt or water etc.
Water droplets in base of fuel tank may stay until a spirited drive around a corner disturbs it into the fuel line.
Sometimes if you have an inline fuel filter it may be possible to see it and if carb cleaned it should show.
Strange other mechanic smelling petrol unless carb needle float jet sticking, that could give loss of power, but usually would not idle , instead it would choke it's self up as though the manual choke had been left out, plus strong petrol smell.

 

[Bubins]

I think he did it to see if it helped, there was no mention of any dirt/water cleaned from the carb.

There are no issues I can note at idle. Only issues are when driving / depressing accelerator but the issue only presents itself occasionally.

When the car was revving low in neutral the revs stayed steady, at the same level, but a lot lower than they should've been considering I had the accelerator pedal fully depressed.

 

[bugsymike]

I think he did it to see if it helped, there was no mention of any dirt/water cleaned from the carb.

There are no issues I can note at idle. Only issues are when driving / depressing accelerator but the issue only presents itself occasionally.

When the car was revving low in neutral the revs stayed steady, at the same level, but a lot lower than they should've been considering I had the accelerator pedal fully depressed.

That sounds more like a fuel blockage, but unusual for it to clear it's self.

 

[StMarks]

Blocked/deteriorating main filter in the fuel tank ????

 

[Bubins]

Could it be the clutch slipping?

 

[Ant Knox]

Could it be the clutch slipping?

I'd expect the revs to rise if your clutch was slipping, since friction is lost between the engine and transmission.

 

[the hobbler]

Blocked/deteriorating main filter in the fuel tank ????

There are, as standard, 3 filters in the 500's fuel system----the sender unit in the fuel tank, in the top of the fuel-pump and in the top of the carb. I would suggest that all 3 are checked, especially the filter on the tank unit which is often ignored. Is there any small particles of muck (or rust) floating around in your fuel tank? If there is, not only can it block the filters, but can also hold the needle-valve in the carb open (until it is flushed through)---this will make the engine run rich, and not pick up

 

[Goldnrust]

All good thoughts above, but I would also add to the list the possibility of a damaged spark plug or plug lead causing the engine to run temporarily on one cylinder?

 

[fiat500]

All good thoughts above, but I would also add to the list the possibility of a damaged spark plug or plug lead causing the engine to run temporarily on one cylinder?

Spark plug change is my new"go-to" for mysterious faults.