bike back fires when letting off

sarw15 · 06-22-2008, 09:59 PM

Ok i spent the weekend doing lots of mods

replace carb jets to 105s

cleand carb smooth for intake and air flow

Cleand ex pipe and took the stuff out from center of pipe looked like bees nest.

changed air cleaner to K&N

check timing

now bike has great power put when I let off it back fires

any one give me a clue??

yurkia · 06-22-2008, 10:22 PM

check for air leaks around your exhaust head.

sarw15 · 06-22-2008, 10:55 PM

clean no leak checked that 1st thing but good thinking

winnipegmike · 06-22-2008, 11:24 PM

I think its running too lean.

TeamCheap · 06-23-2008, 05:47 AM

It may be lean.
Check the spark plug it should tell you how its running.

If you changed the air filter and somewhat gutted the exhuast then you may have to go a bit larger on the main jet still.

When I did my K&N filter and changed the exhaust pipe to a free flowing one I went from a 98 main to a 115 just to get it to run good again.

But you really have to tune it to what YOURS needs to get it right.

sarw15 · 06-23-2008, 07:59 AM

Ok thanks I will check it to night to see how lean it may be.

On the ride to work today ran great hit 90 KMH with easy
one thing I was trying to do was get some of the heat off the pipe and I think it helped.

tonight I will pull the pull hope its no I dont have any more jets I would have to order one :roll:

elroyjetsn · 06-23-2008, 08:22 AM

Maybe check idle mixture and adjust some for the new jet.

katoranger · 06-23-2008, 08:32 AM

I think you will want a larger jet like. The 108 seems to be working good in mine, but I think I could go one step larger.

What elevation are you at. This will make a difference also.

Allen

sarw15 · 06-23-2008, 08:54 AM

not sure of the elevation I'm in San Antonio, Texas about 120 miles from the coast

DesertDog · 06-23-2008, 09:11 AM

yes check the elevation, go to yur local bike dealer, (honda,suzuki,etc....)
ask them what jet size they're runnin in there bikes, mikuni jets are an almost perfect fit to these carbs,

the local dealers carry'em and i use'em, take yur's in to matchup the head and length, the pitch will be off about 1 turn from being tight, you wont strip it out.

i thought at lower elevations you run a much bigger jet and higher elevations a smaller jet,

my sons 250ccPR mx runs a 105 main with a 30mm carb at 5600ft thats what the honda dealer said he runs in his bikes up here .

i run a 122 main in my 300ccPR quad and the plug is medium brown but i also have a 42mm carb needed for for the 300cc.

so it all depends on elevation and what size a carb you run with the main jet

if in texas ?? my guess, buy afew jets from the dealer and test'em out as you step up in sizes, a 115 main sounds about right

i also run a dial-a-jet on my quad so i dont have to mess with jets ever again .

DD

06-22-2008, 09:59 PM	#1
sarw15 Join Date: Apr 2008 Location: Texas, San Antonio Posts: 106	bike back fires when letting off Ok i spent the weekend doing lots of mods replace carb jets to 105s cleand carb smooth for intake and air flow Cleand ex pipe and took the stuff out from center of pipe looked like bees nest. changed air cleaner to K&N check timing now bike has great power put when I let off it back fires any one give me a clue?? __________________ Larry 2008 Roketa RKM-200E5, 200cc
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06-22-2008, 10:22 PM	#2
yurkia Join Date: May 2008 Location: New Franklin, Missouri Posts: 243	check for air leaks around your exhaust head. __________________ '09 Kawasaki KLR 650 '07 Zongshen 200cc Dirt Bike K&N cone filter, FMF Powercore Exhaust, Moose Barkbusters & lotta threadlock.
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06-22-2008, 10:55 PM	#3
sarw15 Join Date: Apr 2008 Location: Texas, San Antonio Posts: 106	clean no leak checked that 1st thing but good thinking __________________ Larry 2008 Roketa RKM-200E5, 200cc
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06-23-2008, 07:59 AM	#6
sarw15 Join Date: Apr 2008 Location: Texas, San Antonio Posts: 106	Ok thanks I will check it to night to see how lean it may be. On the ride to work today ran great hit 90 KMH with easy one thing I was trying to do was get some of the heat off the pipe and I think it helped. tonight I will pull the pull hope its no I dont have any more jets I would have to order one :roll: __________________ Larry 2008 Roketa RKM-200E5, 200cc
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06-23-2008, 08:22 AM	#7
elroyjetsn Join Date: Mar 2008 Location: West Virginia Posts: 629	Maybe check idle mixture and adjust some for the new jet. __________________ Wayne Wildfire WF300-SP
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06-22-2008, 11:24 PM	#4
winnipegmike Join Date: Oct 2007 Location: Winnipeg, Canada Posts: 59	I think its running too lean.
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06-23-2008, 05:47 AM	#5
TeamCheap Join Date: Jun 2006 Location: directly under the earths sun............NOW Posts: 2,302	It may be lean. Check the spark plug it should tell you how its running. If you changed the air filter and somewhat gutted the exhuast then you may have to go a bit larger on the main jet still. When I did my K&N filter and changed the exhaust pipe to a free flowing one I went from a 98 main to a 115 just to get it to run good again. But you really have to tune it to what YOURS needs to get it right.
	0

06-23-2008, 08:32 AM	#8
katoranger Join Date: May 2007 Location: Altamont, Kansas Posts: 15,103	I think you will want a larger jet like. The 108 seems to be working good in mine, but I think I could go one step larger. What elevation are you at. This will make a difference also. Allen __________________ You meet the nicest people on a Honda Clone.
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06-23-2008, 08:54 AM	#9
sarw15 Join Date: Apr 2008 Location: Texas, San Antonio Posts: 106	not sure of the elevation I'm in San Antonio, Texas about 120 miles from the coast __________________ Larry 2008 Roketa RKM-200E5, 200cc
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06-23-2008, 09:11 AM	#10
DesertDog Join Date: Apr 2008 Posts: 782	yes check the elevation, go to yur local bike dealer, (honda,suzuki,etc....) ask them what jet size they're runnin in there bikes, mikuni jets are an almost perfect fit to these carbs, the local dealers carry'em and i use'em, take yur's in to matchup the head and length, the pitch will be off about 1 turn from being tight, you wont strip it out. i thought at lower elevations you run a much bigger jet and higher elevations a smaller jet, my sons 250ccPR mx runs a 105 main with a 30mm carb at 5600ft thats what the honda dealer said he runs in his bikes up here . i run a 122 main in my 300ccPR quad and the plug is medium brown but i also have a 42mm carb needed for for the 300cc. so it all depends on elevation and what size a carb you run with the main jet if in texas ?? my guess, buy afew jets from the dealer and test'em out as you step up in sizes, a 115 main sounds about right i also run a dial-a-jet on my quad so i dont have to mess with jets ever again . DD __________________ DesertDog
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