Car seems to start normally when warm

When cold (40 degrees or below) I can get car to start hesitantly after numerous pedal pumps to prime. It begins to run when motoring starter but as soon as I release key to run position the engine suddenly dies abruptly as if being switched off. I can eventually get it to run after very persistent motoring on the starter until it begins to clear and will finally run in the run position .

It just seems that the run/ignition circuit is significantly weaker in the run position than in the start position, like maybe the run contacts are high resistance or bad ground??

Are there two separate contacts in the ignition switch?? One for run and one for run/start??

Can the switch be opened and checked/cleaned??

Thanks.

If the engine has Weber or Zenith carbs, there's no choke. When cold, you need to pump the throttle multiple times to get it to go. And let it warm up for a couple minutes before setting off. Otherwise, you'll be heel and toeing the thing to keep it running. I'd also look at the carb acceleration plungers to make sure they aren't clogged.

Thanks. Webers. I am completely familiar with how the carbs work and using accelerator circuit to “prime” the engine on cold starts. It is the way the engine completely dies when releasing out of the starter engaged mode that has me baffled.

It looks like the best alternative is to just replace the electrical side of the ignition switch. Thanks again.

There is a good chance it's the ignition switch. Is there a way for you to hot wire the ignition in the engine compartment and use the key to activate the starter?

That’s a good idea. Might be able to jumper 12v to the ignition items directly or back at the relay board and run them hot while I engage the starter with the key.

Might just use the old R&R troubleshooting method and replace the electrical side of the ignition switch.

Anybody have any tips on the best ignition switch of the various ones available? Would like to avoid the worst of the cheap repop junk if possible

Certainly sounds like the switch,you can take them apart (tricky) but worth doing if just dirty inside.

The grease inside them gets caked up and rubs off the contacts over time causing them to wear or burn due to poor contact as the springs struggle to apply good contact .

An expensive part so certainly worth trying to fix it,be carefully pulling it apart as the parts can fly out if you remove the cover too quickly,good luck.

This sounds normal for Webers in cold weather. There were cold days at the track (in the 30's) when the first attempt at start-up in the morning had the 911's and 914/6's passing around the starting fluid to get going.

However, if this cold weather behavior is something new then the ignition side may be the culprit.

Thanks Tub, based on the idea they can be disassembled I’ll probably try to autopsy the orginal switch and if it goes bad replace it.

Let you all know what I find

Could you hook up a 12 volt light or voltmeter to see if you have consistent voltage at the ignition or if it drops? However, the lack of chokes can require quite a lot of pumping of the accelerator until the engine warms up. The hand throttle helps, but not enough in cold weather.

I have 40 IDAs and have never had that experience. When sitting for weeks, (empty float bowls) or very cold it might take 3 tries to get it running, but after it does start it holds its idle. Having it start like a Toyota is not realistic with carbs but that doesn’t sound like your issue.

Definitely would try jumping 12v to the ignition before diving into the switch. I'm struggling to understand how there could be a relationship between the switch function and temperature. If the switch works when warm, I don't see why it wouldn't when cold. A jumper would prove / disprove the theory that its the switch.

Sounds about the same as my Weber’s before, now PMO’s.