TOPIC: Air Temp impact to performance

Does more extreme (hot or cold) air temp play a significant role in running & or idle performance? I wanted to run some tests today but it's 30 degrees out.....

The cold, denser air will make the engine run leaner.

Long time ago I rebuilt a 1350 Merc and ran it out on the bay in November when temps were down in the 30's. I had installed one-size-larger main jets for break-in and it ran pretty good.

Skip to next summer when it's 70+ out, I couldn't even get the boat on plane 'cause the main jets were overly-rich for the air temperature.

I reinstalled the stock .0785 jets and it ran great! Of course, that was back in the days of "real" gas and I'd expect that if you were running on gasohol, the effect would be even worse, since you're already running lean-by-default on Corn Squeezins!

The same motor on gasohol would probably have to have .080" main jets just to keep from frying pistons, in "normal" air temps.

If you were running an older motor with adjustable hi-speed jets, it'd be easy to compensate for any air temp/fuel differences. A "modern" motor with fixed hi-speed jets might not be quite so accomodating.

As for me I think I'll just stick to summer boating!

Cheers.........ed

Thanks! Your comments explain (perhaps) an incident two seasons ago where I went out early in the morning. By afternoon the temps went into the 100's . I've no bimminy top so said 'the heck with this' and on the return trip the motor ran like I was towing a barge. The next day temp were better (80's) and she ran like a champ.

I'm not planning on going out in the water, just some ignition tests in the street on water-muffs as I tinker around with an experimnental ignition.