Why do engines stop immediately after starting


John’s other point about fuel consumption on startup being high: two main factors there. First, which is still true today, you need a rich fuel/air mixture for a cold start. Fuel-injected engines do that automatically - like pulling the manual choke out in a really old car. Remember doing that? But that doesn’t apply restarting in traffic.

Secondly, when John was told this stuff as an apprentice in the 1980s, cars still had carburettors: Remember those? And carburettors had several imperfections, which is why they’ve been superseded. One of those one of which was when you opened the throttle, manifold vacuum drops, and that’s kind of inconvenient because you’re also using that vacuum to deliver the fuel through the carburettor.

So basically, fuel delivery stalls on the grid - just when you need more fuel. So that’s bad.

So if you don’t deal with that, in an engineering sense, it causes a bit of a flat spot - a hesitation - before the engine starts to pick up again. It’s like the engine has a stutter and then decides to get going. So, the conventional fix, the means of dealing with that, was the accelerator pump piston in the carbie. It’s designed to squirt in a bit of extra fuel to cure the stutter. To take it away.

Quite a bit of extra fuel though, which was somewhat wasteful - through the prism of contemporary engine design and fuel consumption standards.

So, if you’re as old as me - ie., older than Facebook minus 30 - you remember the convoluted ritual dad had to go through to start the family car. You remember fondly, perhaps, the arguments he had with mum, imparting this ‘knowledge’ so she could also operate the family chariot.

You know the drill: choke at three-quarters (not eleven sixteenths or seven eighths), two pumps on the gas, count ‘one potato, two potato’, pray, start - like that, hopefully. That’s all gone now - a fuel injected engine is always ready to go. And it does all that crap automatically. Thankfully.