Reluctant cold start (continued)

[Donkey]

Hi folks,
Whilst tinkering under the bonnet yesterday, I noticed that the fuel filter had very little fuel in it.
Recently on here I'd identified a cold start problem and am now wondering if this is the cause. Once warmed-up the car runs superbly.
Being at the highest point I guess that any air ingress would show itself in the filter, but where would I start looking? There is no evident fuel leak.
The pump is working OK, it's a new SU electronic fitted recently

Any thoughts?

Brian

[barkerwilliams]

Brian,

The under bonnet filter is never full, even if you invert it and purge the air once you turn your back the air returns. When the car is hot and the ignition is turned off the fuel heats / evaporates, the carb floats drop, the needle valve then allows air into the plumbing, then gravity drains back to the tank.

If the pump was drawing air and sending to the filter then at speed you would notice a stutter in the engine as it ran short of petrol, if there is a plumbing leak then the fuel would leak out when under pressure.

Assuming by cold start you mean at least overnight then when you come to do a cold start turn the ignition on and listen to the pump ticking. Depending on how much fuel is needed to refill the plumbing it may tick for 20-30 seconds. Then you can try and start the engine.

So the air is nothing to worry about unless the filter does not have 50%'ish fuel when the engine is running, if the cold start problem persists look elsewhere.

If by cold start you mean the car left for an hour or so then that is fairly common when the engine needs a couple or three cranks to get it to fire.

If you have lots of air in the filter when running it is possible that the pump inlet washer is not fully sealing and the pump is drawing both air and petrol, but then the boot would really smell of fuel not just the usual whiff.



Alan

[Donkey]

Brian,

The under bonnet filter is never full, even if you invert it and purge the air once you turn your back the air returns. When the car is hot and the ignition is turned off the fuel heats / evaporates, the carb floats drop, the needle valve then allows air into the plumbing, then gravity drains back to the tank.

If the pump was drawing air and sending to the filter then at speed you would notice a stutter in the engine as it ran short of petrol, if there is a plumbing leak then the fuel would leak out when under pressure.

Assuming by cold start you mean at least overnight then when you come to do a cold start turn the ignition on and listen to the pump ticking. Depending on how much fuel is needed to refill the plumbing it may tick for 20-30 seconds. Then you can try and start the engine.

So the air is nothing to worry about unless the filter does not have 50%'ish fuel when the engine is running, if the cold start problem persists look elsewhere.

If by cold start you mean the car left for an hour or so then that is fairly common when the engine needs a couple or three cranks to get it to fire.

If you have lots of air in the filter when running it is possible that the pump inlet washer is not fully sealing and the pump is drawing both air and petrol, but then the boot would really smell of fuel not just the usual whiff.



Alan

Alan, just the sort of response I was looking for, thanks.

Every day's a learning day.

Kind regards,

Brian