Inertia switch

[Donkey]

Hi folks,
I read sometime ago on the FORUM, that one way of overcoming a hot start problem was to leave the engine running and use the I S to empty the system of fuel before turning the ignition off.
When I tried it there was no lag, the engine immediately stopped and it didn't solve the problem.
Shouldn't I expect the engine to run on for a short while when the pump is cut off?

Answers, as always, really appreciated.

Brian

[Andes]

Is there a possibility a previous owner also wired the ignition into the switch.....

[Matt Cook]

Is your electronic ignition feed taken from the switched side if the inertia switch? That would kill the engine, it should run on while the float chambers empty.

[Donkey]

Sounds like a possibility, I'll look into it, tomorrow. Thanks for now.

[richardthestag]

Hi folks,
I read sometime ago on the FORUM, that one way of overcoming a hot start problem was to leave the engine running and use the I S to empty the system of fuel before turning the ignition off.
When I tried it there was no lag, the engine immediately stopped and it didn't solve the problem.
Shouldn't I expect the engine to run on for a short while when the pump is cut off?

Answers, as always, really appreciated.

Brian

it will run for as long as it takes the fuel lines and float chamber to empty. could be 20 seconds plus

re hot start, have you still got viscous fan fitted?

[mallardstag]

it will run for as long as it takes the fuel lines and float chamber to empty.

...only if the ignition power feed has not been wired to the output of the inertia switch (as is very common for electronic ignition) as rightly pointed out by Matt above.

[Andes]

Just a thought, in case anyone is thinking of wiring their electronic ignition into the switch, would it not be better to allow the engine to run for those 20 or so seconds and allow any potential fire risk to be reduced by ridding the engine and fuel lines of any remaining fuel....

[022Dave]

Just a thought, in case anyone is thinking of wiring their electronic ignition into the switch, would it not be better to allow the engine to run for those 20 or so seconds and allow any potential fire risk to be reduced by ridding the engine and fuel lines of any remaining fuel....

Sounds alright at first, but the inertia switch is there to cut the fuel supply in an accident, so 20-or-so seconds of pumped fuel spraying about would be disastrous on a hot engine.

I have an occasional hot start problem, and I'm thinking of adding a switch under the dashboard to isolate the pump before shutting down the engine, to see in that helps, but I don't want the function of the inertia switch to be compromised.

Dave

[Andes]

Hi Dave, I understand where you’re coming from but once the pump is cut off by the inertia switch the engine is just burning what’s left in the fuel lines and engine......much safer I would have thought than having fuel sitting in a pipe that has just split and now pours over the engine or out onto the road.

[mallardstag]

I have an occasional hot start problem

Have you checked your fuel pressure yet?

[022Dave]

Have you checked your fuel pressure yet?

Yes; I fitted a FilterKing last year, which has improved the hot start problem, but occasionally it throws a strop. I'm guessing that the fuel in the carburettor float bowl expands, and runs into the manifold, causing an over-rich mixture at startup. I thought that shutting off the fuel before switching off the engine (not necessarily letting it splutter to a halt) may stop the expansion down into the manifold.

Dave

[StagJonno]

Yes; I fitted a FilterKing last year, which has improved the hot start problem, but occasionally it throws a strop. I'm guessing that the fuel in the carburettor float bowl expands, and runs into the manifold, causing an over-rich mixture at startup. I thought that shutting off the fuel before switching off the engine (not necessarily letting it splutter to a halt) may stop the expansion down into the manifold.

Dave

Sounds a fancied approach - will be interested to hear how you get on. It also gives you an added anti-theft function. Bear in mind that the fuel pump feed is unfused from the battery so recommend that the connectors are insulated adequately to avoid short circuits.

I might do something similar - the perfume smell of petrol (from evaporation from the carbs after a run) sometimes manages to get into the house, not to universal acclaim I'm sad to say

Jonno

[022Dave]

Sounds a fancied approach - will be interested to hear how you get on. It also gives you an added anti-theft function. Bear in mind that the fuel pump feed is unfused from the battery so recommend that the connectors are insulated adequately to avoid short circuits.

I might do something similar - the perfume smell of petrol (from evaporation from the carbs after a run) sometimes manages to get into the house, not to universal acclaim I'm sad to say

Jonno

Same in mine, Jonno. I keep getting grief from Mrs C after playtime, so I now leave the garage door open for a while to let it purge! Hadn't considered the anti-theft benefit, or the lack of a fuse.

Dave

[Donkey]

As suggested, it is wired via the electronic ignition. Why would someone have done that?
I would assume that at factory fit, a cable would be fed to the I S location and according to my WM it should be a white cable. I have found a pair of grey wires cut off close by, but that's all. Any ideas?
I would like to reinstate the original arrangement or, as others have suggested, have a switch inside the car. Thoughts and ideas always welcome.

Brian

[DJT]

As suggested, it is wired via the electronic ignition. Why would someone have done that?

The electronic ignition has to be supplied from somewhere. The output of the inertia switch is a reasonable choice as it is local and gives the added advantage of stopping the engine instantly in the event of a crash which triggers the switch, rather than the engine continuing to run until the fuel runs out in the carbs. Arguments for and against either way. I’ve been running mine this way for 30 years and never had a spurious trip yet caused by speed humps or potholes.