performance on really hot days

greatwhiteninja · July 20th, 2011, 08:43 PM

noticed today my bike was sputtering a little at like 11k+ rpms in like 4th,5th gears.. lower rpms were fine and lower gears i could redline and didnt notice any sputtering. never done that before but it has been EXTREMELY hot and humid the last 2-3 days.. today like low to mid 90's with a heat index of around 100ish.. suppose to have heat index of like 115 come friday! just wandering if this is the cause or should look at a jetting issue with the bike? has full exhaust/110 mains/pod filters.. been fine up until it got really hot out.. at least never sputtered before.

alex.s · July 21st, 2011, 12:30 AM

i first noticed this when my 50cc engines seemed to run better when it was colder out... someone who seemed to know what they're were talking about once explained it to me that it had something to do with jetting but i've never been good with that sort of thing. something about when its hotter the pressure of the air is different expands which changes the amount of oxygen that mixes with the fuel, changing the air/fuel ratio... it was over my head... all i know is, when we would tune our carbs at a certain temperature or altitude, when that temp or alt. changed, things got funky

Cuongism · July 21st, 2011, 01:55 AM

Many environmental factors affect the air portion of your jetting (air/fuel ratio). More oxygen means bike runs leaner while less oxygen means bike runs richer.

Hotter temps means air is less dense so less oxygen (bike runs richer).

Humidity is not as big a factor as temp or altitude, but higher humidity also decreases oxygen levels so bike runs richer.

You didn't mention altitude, but that's the other environmental factor. The higher you go up in elevation, the less dense air gets which causes your bike to run richer.

greatwhiteninja · July 21st, 2011, 05:45 AM

yeah im at sea level.. ill wait for the temps to drop a little and see how it runs before i make any changes.. so sputtering would be a sign of too rich then?

DaBlue1 · July 21st, 2011, 06:21 AM

Quote:

Originally Posted by greatwhiteninja

yeah im at sea level.. ill wait for the temps to drop a little and see how it runs before i make any changes.. so sputtering would be a sign of too rich then?

Is it sputtering or surging? The engine can surge/bog at WOT if it is too rich and sputter if starving for fuel like it is about to cut out. At 11k rpms in 4th & 5th you are approaching max power output anyway. Are you having any power lose?
Look at your plugs and exhaust to see if they are black. From what you describe it sounds like you may be a little rich for conditions.

SPG · July 21st, 2011, 12:42 PM

The clue that it is too rich (instead of lean) is that it ran fine at the cooler temps and is less happy in the warm.

My racebike has a wideband O2 sensor (mixture gauge) so I can stay on top of the jetting. I don't have pod filters, just stock box without snorkel, and a full Leo Vince exhaust. I was running a 98 main (stock) for this spring, and dropped it to a 95 as we ease into summer (70 degrees and sea level). I'm still running at 12.5 to 13:0 air/fuel which is rich and about perfect for max power.

Your bike would likely be happier with a 105 main in the summer (and maybe year round).

-Sean

July 20th, 2011, 08:43 PM	#1
greatwhiteninja Ridin Dirty Name: Ed Location: Delaware Join Date: Jun 2011 Motorcycle(s): 2011 white se 250r , 2008 zx6R Posts: 921	performance on really hot days noticed today my bike was sputtering a little at like 11k+ rpms in like 4th,5th gears.. lower rpms were fine and lower gears i could redline and didnt notice any sputtering. never done that before but it has been EXTREMELY hot and humid the last 2-3 days.. today like low to mid 90's with a heat index of around 100ish.. suppose to have heat index of like 115 come friday! just wandering if this is the cause or should look at a jetting issue with the bike? has full exhaust/110 mains/pod filters.. been fine up until it got really hot out.. at least never sputtered before. __________________________________________________ #1

July 21st, 2011, 12:30 AM	#2
alex.s wat Name: wat Location: tustin/long beach Join Date: Sep 2009 Motorcycle(s): wat Posts: Too much. Blog Entries: 5 MOTM - Oct '12, Feb '14	i first noticed this when my 50cc engines seemed to run better when it was colder out... someone who seemed to know what they're were talking about once explained it to me that it had something to do with jetting but i've never been good with that sort of thing. something about when its hotter the pressure of the air is different expands which changes the amount of oxygen that mixes with the fuel, changing the air/fuel ratio... it was over my head... all i know is, when we would tune our carbs at a certain temperature or altitude, when that temp or alt. changed, things got funky __________________________________________________

July 21st, 2011, 05:45 AM	#4
greatwhiteninja Ridin Dirty Name: Ed Location: Delaware Join Date: Jun 2011 Motorcycle(s): 2011 white se 250r , 2008 zx6R Posts: 921	yeah im at sea level.. ill wait for the temps to drop a little and see how it runs before i make any changes.. so sputtering would be a sign of too rich then? __________________________________________________ #1

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July 21st, 2011, 01:55 AM	#3
Cuongism ninjette.org certified postwhore Name: Cuong Location: San Diego Join Date: Jul 2010 Motorcycle(s): 2008 Ninja 250r, 2007 Daytona 675 Posts: A lot.	Many environmental factors affect the air portion of your jetting (air/fuel ratio). More oxygen means bike runs leaner while less oxygen means bike runs richer. Hotter temps means air is less dense so less oxygen (bike runs richer). Humidity is not as big a factor as temp or altitude, but higher humidity also decreases oxygen levels so bike runs richer. You didn't mention altitude, but that's the other environmental factor. The higher you go up in elevation, the less dense air gets which causes your bike to run richer.

July 21st, 2011, 12:42 PM	#6
SPG ninjette.org member Name: Sean Location: Seattle Join Date: Aug 2010 Motorcycle(s): 250 Ninjette Posts: 94	The clue that it is too rich (instead of lean) is that it ran fine at the cooler temps and is less happy in the warm. My racebike has a wideband O2 sensor (mixture gauge) so I can stay on top of the jetting. I don't have pod filters, just stock box without snorkel, and a full Leo Vince exhaust. I was running a 98 main (stock) for this spring, and dropped it to a 95 as we ease into summer (70 degrees and sea level). I'm still running at 12.5 to 13:0 air/fuel which is rich and about perfect for max power. Your bike would likely be happier with a 105 main in the summer (and maybe year round). -Sean