Backfire after exhaust install?

chef · April 2nd, 2011, 03:33 AM

Hi guys,
Am wondering what causes exhaust backfire on start up?
Last month i got a great deal on a used yoshi system.
Had it installed,jet kit installed & was no problem until this week,when it has suddenly developed a huge backfire several times when starting.
Conditions remain the same,no choke ( warm weather here in Bali )
Will be installing the Sportisi hugger next week,great service from them & cant wait !

Cheers,
Matt

chef · April 2nd, 2011, 03:39 AM

Shoulda checked before posting!
Seems its a common problem & nothing too serious to worry about but yeah,it did scare the chocolate outta me too!

wayanlam · April 2nd, 2011, 03:50 AM

plug up the kleen air hose, there are several threads on doing that already

warlord · April 2nd, 2011, 05:29 AM

^^^ +1 on Kleen Air delete

wvninja · April 2nd, 2011, 09:48 AM

remove kleen air system, and snorkle

maybe do a carb shim or new jets. removes a lot of that pop on decel and startup.

kkim · April 2nd, 2011, 09:53 AM

start up backfire will occur with a stock or an aftermarket exhaust. removing the Kleen system doesn't help this at all.
http://www.ninjette.org/forums/showthread.php?t=15025&

learn to live with it and chalk it up to one of the mysteries of the 250R. have you heard the bike whining, yet?

gfloyd2002 · April 2nd, 2011, 09:55 AM

Backfiring often means that you are too lean, though there is some degree of backfire that is just going to happen regarless because that is just the way the bikes are. (Technically not a backfire, but burning mixture remaining in the cylinder until the beginning of the next intake stroke when it can ignite the incomming air/fuel mixture.) This is common when you put a new exhaust on if you haven't adjusted your fuel system properly. What happens is that the exhaust lets air flow more freely through the engine and your air/fuel ratio gets out of whack. Too much air, too little fuel in the mix. So you may need to increase the fuel flow by opening up your carb mix screws or getting bigger jets in.

Also, removing the kleen system or snorkel won't help. That is going to add even more air into the mix and lean you out further. You are going to need to either restrict airflow (a bad idea) or increase fuel flow (the way to go) if this is more than the typical occassional ninjete backfiring.

April 2nd, 2011, 03:33 AM	#1
chef ninjette.org member Name: Matt Location: Bali Join Date: Dec 2010 Motorcycle(s): 1965 Honda S90 , 2010 Ninja 250,2012 Vespa LX 150(Yes,a vespa!) Posts: 177	Backfire after exhaust install? Hi guys, Am wondering what causes exhaust backfire on start up? Last month i got a great deal on a used yoshi system. Had it installed,jet kit installed & was no problem until this week,when it has suddenly developed a huge backfire several times when starting. Conditions remain the same,no choke ( warm weather here in Bali ) Will be installing the Sportisi hugger next week,great service from them & cant wait ! Cheers, Matt

April 2nd, 2011, 03:50 AM	#3
wayanlam ninjette.org certified postwhore Name: Wayan Location: Bali - Indonesia Join Date: Apr 2009 Motorcycle(s): 2014 Z250 Posts: A lot.	plug up the kleen air hose, there are several threads on doing that already __________________________________________________ Kawasaki Z250, Bored up to 300cc with 12.8 CR, 41hp at wheel 27nm torque, Two bros full exhaust with DB killer Dynojet Power Commander V, KnN Open filter, intake and exhaust ported, Puig Windshield

April 2nd, 2011, 09:48 AM	#5
wvninja ninjette.org sage Name: Nate Location: west virginia Join Date: Apr 2010 Motorcycle(s): 2009 Honda CBR600RR Posts: 633	remove kleen air system, and snorkle maybe do a carb shim or new jets. removes a lot of that pop on decel and startup. __________________________________________________ "Riding a motorcycle is like playing sports, not everyone is cut out for it." - WVNinja

April 2nd, 2011, 09:55 AM	#7
gfloyd2002 User Title Free Since '12 Name: Floyd Location: Barbados Join Date: Dec 2010 Motorcycle(s): '10 Ninja 250R Special Edition Green Posts: A lot. Blog Entries: 13 MOTM - Feb '12	Backfiring often means that you are too lean, though there is some degree of backfire that is just going to happen regarless because that is just the way the bikes are. (Technically not a backfire, but burning mixture remaining in the cylinder until the beginning of the next intake stroke when it can ignite the incomming air/fuel mixture.) This is common when you put a new exhaust on if you haven't adjusted your fuel system properly. What happens is that the exhaust lets air flow more freely through the engine and your air/fuel ratio gets out of whack. Too much air, too little fuel in the mix. So you may need to increase the fuel flow by opening up your carb mix screws or getting bigger jets in. Also, removing the kleen system or snorkel won't help. That is going to add even more air into the mix and lean you out further. You are going to need to either restrict airflow (a bad idea) or increase fuel flow (the way to go) if this is more than the typical occassional ninjete backfiring. __________________________________________________ "Improvement makes straight roads, but the crooked roads without improvement, are roads of genius." — William Blake

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April 2nd, 2011, 03:39 AM	#2
chef ninjette.org member Name: Matt Location: Bali Join Date: Dec 2010 Motorcycle(s): 1965 Honda S90 , 2010 Ninja 250,2012 Vespa LX 150(Yes,a vespa!) Posts: 177	Shoulda checked before posting! Seems its a common problem & nothing too serious to worry about but yeah,it did scare the chocolate outta me too!

April 2nd, 2011, 05:29 AM	#4
warlord ninjette.org guru Name: war Location: north chicago burbs Join Date: Jan 2011 Motorcycle(s): 2014 Ducati Panigale 899 Posts: 325	^^^ +1 on Kleen Air delete

April 2nd, 2011, 09:53 AM	#6
kkim Join Date: Nov 2008 Posts: Too much.	start up backfire will occur with a stock or an aftermarket exhaust. removing the Kleen system doesn't help this at all. http://www.ninjette.org/forums/showthread.php?t=15025& learn to live with it and chalk it up to one of the mysteries of the 250R. have you heard the bike whining, yet?