I have to disagree with this point Shell. If the engine's temp is higher than gas's flashpoint, then it would be flashing over when it enters under normal operating conditions, which is hardly what we what, and we know that doesn't happen.

 

Yeah, that part came out all wrong. We wouldn't need spark plugs if that was case. Would the engine temperature effect the rate of evaporation?

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yup... boiling point certainly would come into play here. A hot engine will definitely increase the rate of evaporation.

 

I just saw this.... what makes you think this?

water temperature adjustments are definitely made to fuel trim but I'm unaware of the trim being subject to RPM.

 

with that mindset, still more fuel would wash into the engine during run down.

easy translation, 3000RPMs = 3000 revolutions to eject vapors and unspent fuel from the engine. 800RPMs = 800(truth being the rotors only are turning at 1/3 that rate. 1000 full rotor rotations at 3k versus 267 rotations at 800rpms) revolutions to eject near the same amount in the intake manifold after injectors are shut off. there may be a few cycles where the fuel is injected that doesn't reach the plugs before they have already shut down.

a full up to temp engine will vaporize the fuel from the rotor housings and iron walls, a cool engine will have a film of fuel on the internals because the engine isn't hot enough to vaporize it before it sticks.

equivalent would be snow hitting the ground when the ambient temp is 40F, it may touch ground but it will soon vaporize. this is how i see a hot engine reacting where a cold engine would be snow hitting the ground in sub 32F climate and staying put until the snow plow comes and sweeps it off, leaving ice. friction may melt some of that ice or at least push it out of the way.

but you're beginning to see why this debate really has no concrete proof either way.

 

nah, I just floundered on flash vs boiling point lol.

You're thinking linearly. There is a rate of decay with the engine spooling down. I do agree that some percentage of fuel will definitely be expelled during spool down.

Whether that percentage is significant remains to be seen.

I like Brett's approach because by holding down the gas pedal on startup you're cutting fuel and allowing any unspent fuel in the chambers to ejected prior to attempting a new combustion event.

 

That's a really good point. By turning it off cold, the next startup has two starts worth of flooding.

Mazda apparently likes that, too. One of the features of the 4206f reflash was to delay starting injection until after the engine had spun a couple of times. No need to manually overthink it.

Of course, the delayed injection is to avoid flooding on the current start, not to fix something left over from the last shutdown.

Ken

 

Thank you all for all of your input