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points by AngryData 1 day ago | 0 comments
Unless you are trying to race your car at the drag strip with charged air and hit your best times, that isn't true at all and I don't know why people keep saying it. You think everybody empties their lawn mowers, snow blowers, snowmobiles, generators, etc. every year of gas or before trying to start it up again the next year? No way.

Simpler gas equipment like mowers and generators don't have enough compression to really care about anything but ancient gas, and if you run any vehicle that is multi-fuel capable it can detect and adjust compression based on a fuel's capabilities.

Ive been repairing and fixing junkers of cars, mowers, ATVs, generators, and more for 30 years and not once has bad gas stopped something from running. I only remove it if it was clearly having water raining into the tank. In every other case where I couldn't start something after sitting around for 5+ years, it was from the gas gumming up in the carb or the shitty diaphragm pump, which generally means there is little to no gas left to start with.

I wouldn't even suspect gas of ever being bad unless it was atleast a few years old. If the tank was open it could have evaporated, if the tank was closed it probably ain't great gas but I bet it would still run in anything but a high compression application.

[–] dotancohen 1 day ago
> detect and adjust compression based on a fuel's capabilities.

Spark, not compression.

[–] JshWright 15 hours ago
The spark timing determines how much compression is in the cylinder at the moment the fuel/air mixture is ignited. So, while it's technically true that it's the spark timing that's being adjusted, the thing that is being controlled for is the compression.
[–] dotancohen 2 hours ago
This explanation is an excuse, and does not pass muster. I remember adjusting spark timing with a timing light flashing on the harmonic balancer and turning the distributor by hand. Cars two decades before that, which I never personally serviced but have seen, had spark adjustment controls on the steering wheel.

The term was always called spark adjustment, never compression. Compression is the thing you worry about when milling the heads or exchanging oscillating components (rods, pistons) due to changing the physical geometry of the combustion chamber.

So yes, adjusting the spark timing does technically adjust how compressed the air/fuel mixture is at the moment of ignition. But the term used to describe it has always been "adjusting spark" or "adjusting spark timing" or "adjusting timing". Nobody ever refers to that as "adjusting compression" because the term compression is used to refer to something else.