RM 125 carb issues. - Motorcycle-Journal Forums

BodaciousNick · 05-09-2007, 08:58 PM

Hey, im the owner of a 1980 RM 125. just recently ate the piston and had to repair a few things. thats all done, and the bike is broken in...but the bike has been running really rich with fuel, always has, but it seems a lil' worse now, and might as well fix it since the engine is all in good order now. the mixture ratio is 32:1, which is even more lean than the 20:1 ratio that the clymer book for my bike suggests. I was wondering. does overboring the engine change the dynamics of the carb? I was snooping around the nature coast power sports website and noticed that there is more than one type of jet sets for my carb. i was thinking, are the other jets for various over bore sizes? I have re-adjusted the floats to cut off fuel sooner and it still loads up it seems. I am using good pre-mix oil and gasoline with a 93 octane rating. not the best...but pretty good. maybe i need to adjust the throat needle? im not the sharpest tool in the shed when it comes to tunning a carb...but i can find my way around. any help you can offer would be great. thanks for your time.

~nick

the_privateer · 05-10-2007, 01:13 AM

over-boring, weather, altitude, riding style, humidity, and any modifications are going to affect your jetting.

first i would set the float to the correct level, and repack the silencer if it needs it
now you need to decide where in the rev range you are rich

the pilot jet concerns 0-1/4 throttle ranges, adjustment is made by switching out different size jets

the jet needle concerns 1/4 to 3/4, adjustments are made by moving the clip on the needle, up to lean

the main controls from 1/2-to full throttle, adjusted by switching out for different size jets

a smaller jet will lean out the mixture, usually you want to make steps one size at a time to prevent going too lean and seizing the motor

if you have a manual it will make this all very easy, if not i would either get one, or go to bike bandit or some other parts site where you can get a parts fiche for the carb

BodaciousNick · 05-10-2007, 06:32 PM

yeah, i have a manual by Clymer. its pretty thourough. Thanks for you input. it seems that the exhaust becomes smokiest at the low rpms. close to idle. I have cleaned EVERYTHING! though i live down in FL and the fires in GA have been making it really smokey and cloudy. its also very humid as well. so maybe that leap in climate change is to blame, at least for some part.

Im pretty sure that the pilot jet will be the one to go. ill consult my manual a little more and see what it says. Thanks for your reply!

Harry Palmer · 07-08-2007, 09:08 PM

Try Reading the spark plug,32-1 is alright,93 octane is great,use your manual to confirm your air,fuel screw settings,set your needle clip at the top,All the
smoke your seeing could be from a weak right side crank seal,Drain your trans
oil and measure what you put back in,Ride it like you stole it,for an hour or two
Then redrain and measure what comes out. NO REFEREES NO TIMEOUTS!

05-09-2007, 08:58 PM	#1 (permalink)
BodaciousNick Newbie Joined: May 2007 Bike: 1980 RM 125 Location: Crystal River, FL. good ol' USA Posts: 16	RM 125 carb issues. Hey, im the owner of a 1980 RM 125. just recently ate the piston and had to repair a few things. thats all done, and the bike is broken in...but the bike has been running really rich with fuel, always has, but it seems a lil' worse now, and might as well fix it since the engine is all in good order now. the mixture ratio is 32:1, which is even more lean than the 20:1 ratio that the clymer book for my bike suggests. I was wondering. does overboring the engine change the dynamics of the carb? I was snooping around the nature coast power sports website and noticed that there is more than one type of jet sets for my carb. i was thinking, are the other jets for various over bore sizes? I have re-adjusted the floats to cut off fuel sooner and it still loads up it seems. I am using good pre-mix oil and gasoline with a 93 octane rating. not the best...but pretty good. maybe i need to adjust the throat needle? im not the sharpest tool in the shed when it comes to tunning a carb...but i can find my way around. any help you can offer would be great. thanks for your time. ~nick

05-10-2007, 06:32 PM	#3 (permalink)
BodaciousNick Newbie Joined: May 2007 Bike: 1980 RM 125 Location: Crystal River, FL. good ol' USA Posts: 16	yeah, i have a manual by Clymer. its pretty thourough. Thanks for you input. it seems that the exhaust becomes smokiest at the low rpms. close to idle. I have cleaned EVERYTHING! though i live down in FL and the fires in GA have been making it really smokey and cloudy. its also very humid as well. so maybe that leap in climate change is to blame, at least for some part. Im pretty sure that the pilot jet will be the one to go. ill consult my manual a little more and see what it says. Thanks for your reply! __________________ *Because football, soccer, and baseball require only one* ball.** http://www.myspace.com/space_nicks_is_this

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05-10-2007, 01:13 AM	#2 (permalink)
the_privateer Clunked into first gear Joined: Jul 2006 Bike: 2000 yz125 race prepped Location: bentonville, arkansas, us Posts: 230	over-boring, weather, altitude, riding style, humidity, and any modifications are going to affect your jetting. first i would set the float to the correct level, and repack the silencer if it needs it now you need to decide where in the rev range you are rich the pilot jet concerns 0-1/4 throttle ranges, adjustment is made by switching out different size jets the jet needle concerns 1/4 to 3/4, adjustments are made by moving the clip on the needle, up to lean the main controls from 1/2-to full throttle, adjusted by switching out for different size jets a smaller jet will lean out the mixture, usually you want to make steps one size at a time to prevent going too lean and seizing the motor if you have a manual it will make this all very easy, if not i would either get one, or go to bike bandit or some other parts site where you can get a parts fiche for the carb

07-08-2007, 09:08 PM	#4 (permalink)
Harry Palmer Newbie Joined: Jul 2007 Posts: 17	Try Reading the spark plug,32-1 is alright,93 octane is great,use your manual to confirm your air,fuel screw settings,set your needle clip at the top,All the smoke your seeing could be from a weak right side crank seal,Drain your trans oil and measure what you put back in,Ride it like you stole it,for an hour or two Then redrain and measure what comes out. NO REFEREES NO TIMEOUTS!

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