Difference between running rich and running lean? - KawiForums - Kawasaki Motorcycle Forums
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post #1 of 15 (permalink) Old 09-10-2005, 05:33 AM Thread Starter
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Difference between running rich and running lean?

can someone explain the difference between running rich versus running lean?

thanks

javier
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post #2 of 15 (permalink) Old 09-10-2005, 06:53 AM
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Rich = too much gas
Lean = too little gas
Engines need an ideal ratio of fuel to air to make best power. Generally bikes come from the factory on the lean side, because leaner runs hotter, and hotter usually means lower emissions. Mods like air filters and exhaust systems allow the engine to move more air, making it run even leaner.
That's why a jet kit\power commander is needed to truly take advantage of most engine mods.
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post #3 of 15 (permalink) Old 09-10-2005, 11:35 AM
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I would have to disagree, bikes come from the factory usualy fairly rich.

Rich is safer than lean as lean DOES run hotter, but heat is the no1 enemy of any engine.
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post #4 of 15 (permalink) Old 09-10-2005, 05:33 PM
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We're both right, actually. Bikes(FI bikes, anyway)tend to run lean at low\mid RPMs for economy and emissions, and rich at high RPMs for that margin of safety at heavy loads.
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post #5 of 15 (permalink) Old 09-10-2005, 05:48 PM
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rat is correct if you look at most maps for power commanders there ramming more fuel in at lower rpms and leaning out at higher rpms

map i mad efor mine

the numbers are % more or less fuel added you can see the graph too at the bottem
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post #6 of 15 (permalink) Old 09-10-2005, 09:06 PM
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Quote:
Originally posted by MaDgamEr
I would have to disagree, bikes come from the factory usualy fairly rich.

Rich is safer than lean as lean DOES run hotter, but heat is the no1 enemy of any engine.
you're absolutely right about lean running hotter. but due to emissions issues here in the USA, most bikes are set at the factory to run lean (running hot assists in burning off the remaining exhaust gases) to pass emissions. most folks either jet the carbs or they have the idle mixture screws (not to be confused with the idle adjustment knob)turned out to the full-rich. being the cheapo that i am i went for the latter, which helps with throttle lag but doesn't increase hp by much.
on FI they usually get a power commander and re-map the FI computer.
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post #7 of 15 (permalink) Old 09-10-2005, 09:56 PM
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It really depends what emissions we're talking about actually, i beleve its NOX (oxides of nit) that go up as running a lean mixture.. Other emissions may go up or down depending on what the mixture is.


But to answer the first question. Stochiometric mixture (14.7 parts air to 1 part fuel) As you know air is only has so much oxygen in it, which supports combustion, if you dont have enough air(oxy) to support the combustion the mixture is considered rich, too much fuel, not enough oxy to burn all the fuel.. Vice versa with the lean condition. Running lean also means running hotter, which has been said.. Just like a torch, you add oxygen and the flame can get 10x hotter then just a standard acetylene flame.



Jetting for carbs is what changes this mixture, different circuits for different throttle ranges.. Talk to people who ride snowmobiles in the mountains, we've gone to higher elevations and had to change jets just to get the sleds running decent, and not burning holes in the pistons..
At least with FI the ecm program can be changed quickly, changing pulse width and controlling fuel like that, all we need now is an 02 sensor to see what, if any oxy gen is coming out fo the exhaust..
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post #8 of 15 (permalink) Old 09-10-2005, 10:45 PM
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thanx spitz. i was trying to avoid getting too scientific here. i'm an aircraft mechanic and have a bit of understanding on the air/fuel and various effects of altitude on that mixture. but you did bring up an interesting point with the snowmobiles at altitude. i rode to deals gap via the skyline dr & brp prior to having the idle mixture adjusted and noticed on the mountains that the bike ran much better/smoother.
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post #9 of 15 (permalink) Old 09-11-2005, 12:25 AM
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Really?? How much of an elevation change is there??

Must be a lot different with aircraft huh?? Doesnt the temp dro quite a bit at altitude???

ps- it doesnt really take that much of a cahnge in elevation to make the mixture change does it? Thats one thing i notice.. We rode up to lake of the clouds in UP of michigan.. My friends race sled was acting up A LOT! 10 minutes of riding and it would be really poochy then the next minute he was flying by me, really weird.
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post #10 of 15 (permalink) Old 09-11-2005, 08:48 PM
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Quote:
Originally posted by spitz04
Really?? How much of an elevation change is there??
at one point we were up ~5k feet on the BRP heading towards asheville.

[/quote]Must be a lot different with aircraft huh?? Doesnt the temp dro quite a bit at altitude???[/quote]well as you probably already realize-- cooled air is more dense, but what i learned in powerplant school is that altitude increase has a greater effect than the temp drop on the air density.

[/quote]ps- it doesnt really take that much of a cahnge in elevation to make the mixture change does it? Thats one thing i notice.. We rode up to lake of the clouds in UP of michigan.. My friends race sled was acting up A LOT! 10 minutes of riding and it would be really poochy then the next minute he was flying by me, really weird. [/quote]back in 99(?) i was in AZ and took a trip from tucson to the grand canyon. we were in a brand new plymouth breeze with a FI 4 cyl. on our way to flagstaff their is a pass that takes you to 9K+ feet. by the time we reached the top, we could barely maintain 55mph with the gas pedal floored. alot of vehicles were puttin out black smoke (overly rich)

now this is getting off topic, but anyway, most non-turbocharged airplanes can only maintain cruise up to ~15k feet. tc airplanes can maintain cruise power up to 20-24K feet.
also, piston airplanes usually have a manually controlled mixture control (carb & FI) that the pilot sets at full-rich for take-off/landing and they lean the mixture as req'd as they gain altitude.
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