Technical Another hot motor issue

[Alio]

Hi, I am new to this forum, hopefully I am posting to the right section.

I have a 1968 Autobianchi. It starts and runs well for 20 minutes, then sputters on 4th gear, runs ok for another 2-3 minutes on 3rd, and dies.
Waiting 10 minutes and restarting gives me another 15 minutes of good performance. and so on.
The other discussions talk about creating a fuel return, but my carb does not have that option.
Any help or advice will be appreciated.
Cheers

 

[Greasytrucker]

Hi, I am new to this forum, hopefully I am posting to the right section.

I have a 1968 Autobianchi. It starts and runs well for 20 minutes, then sputters on 4th gear, runs ok for another 2-3 minutes on 3rd, and dies.
Waiting 10 minutes and restarting gives me another 15 minutes of good performance. and so on.
The other discussions talk about creating a fuel return, but my carb does not have that option.
Any help or advice will be appreciated.
Cheers

Are you sure it’s fuel related and not the ignition coil breaking down as it warms up?

 

[Alio]

Are you sure it’s fuel related and not the ignition coil breaking down as it warms up?

No not sure, but why would it work for a while on third gear?

 

[Greasytrucker]

No not sure, but why would it work for a while on third gear?

Less load on the engine in 3rd perhaps so not quite reaching the point as to where it cuts out? Just an idea. How long have you had the car, has it been running ok before in your ownership?

 

[Goldnrust]

No not sure, but why would it work for a while on third gear?

The same logic applies to a fuel delivery issue. If the carb was getting vapour locked, then changing down to third, requiring more RPM wouldn’t necessarily help.

I suspect the changing down gears just means that the engine is require to make less power to keep the car moving and represents a gradual reduction in power being made by the engine.

As already mentioned, ignition coils can fail in a way that only shows up when hot.

Another thing to check is vavle clearences. If they are too tight then you can find that as the engine gets hot and the push rods expand a little, it holds the valves open and looses compression, and therefore power.

Also worth checking the choke mechanism is free and adjusted right to make sure the choke isn’t sticking on.

Conversely, check that the fuel tank is venting properly through the cap. If the vent is blocked then it can cause a vacuum in the tank and fuel flow to stop after a while of driving.

Ultimately it’s all a bit of guess work trying to diagnose over the internet. If you can repeat the issue, then once the engine is hot and not working right, then you could check for spark, compression and fuel flow and try to narrow down the cause that way?

 

[fiat500]

Try with different spark plugs.

 

[Alio]

Thank you Greasytrucker, Goldnrust, and fiat500
I have the Autobianchi since 2011. This problem is only in the last few seasons. I have changed the ignition to electronic, verified the tank venting.
Will try the other suggestions, and let you know of the results.
Cheers

 

[the hobbler]

Thank you Greasytrucker, Goldnrust, and fiat500
I have the Autobianchi since 2011. This problem is only in the last few seasons. I have changed the ignition to electronic, verified the tank venting.
Will try the other suggestions, and let you know of the results.
Cheers

What model of "Autobianchi" do you have? Does it have the 'Giardiniera' engine (flat twin) or the normal 'car' engine? (vertical twin). I ask this because on the normal 'car' vertical twin engine, electronic ignitions have a major problem in that the distributer can get very hot---sometimes exceeding 100C, which is the "wilt" point for ALL electronic ignitions. Try changing it back to 'points' ignition and see how that affects the running---if nothing else, it will eliminate the distributor side of the ignition as the cause of the fault

 

[lazylobster]

As others have said.
Return to points
Replace coil
replace spark plugs, I had one that broke down when it got hot.
I would also replace the rota and arm in the dist. As cheap to do to eliminate.
Oh, spark leads too.

You can get a multimeter on the coil and leads to measure, do cold and when engine hot to see.

R