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Bob KellyIII · April 23rd, 2023, 01:37 PM

Jim: needle shims means the carbs have to come out.... getting the carbs out on that bike is Not EASY ! it's only easy if the carbs are already OUT.... LOL !!!!!
....
Needle shims have never worked for me... they introduce a flat spot in almost every case
when I have tried to use a shim... you mess with the fuel to air ratio when you Shim it
changing it from 14:1 to 12:1 or some thing like that and that is not a good idea to do.
changing the Main jet is by far better if you want to get more or less fuel in it. because it will increase or decrease the voluum but keep the fuel /air ratio the same. in almost every case a flat spot in the throttle opening is due to something else and not the jet needle. they put alot of time and effort to keep the fuel /air ratio correct throughout the RPM Range so the stock carb is usually spot on.... BUT it may well be spot on in a very lean or Rich way throughout the span of RPM and this is not uncommon at all especially with mods to intake and exhaust systems on the bike. if it comes to the point of shimming a needle I have to think something else is very wrong in the system.... it is designed to put out 14:1 fuel air ratio throughout the RPM range and that is a very hard trick to accomplish.... changing the main jet changes that 14:1 ratio through the entire range.... a larger main jet will lower the ratio from like 14:1 to 12:1 and a smaller main jet will increase it like from 14:1 to 16:1.... so In Most cases there is never a need to change the main jet at all... but when changes are made then adjustments have to be made....
for instance: on my XR650L I have been trying to get the Fuel/air ratio Down because it runs very lean for a air cooled bike
it needs a richer mixture to help cool the air cooled engine... so I have increased the main jet size from 150 to 160 and it only changed it a little I may need to go more to something like 165 this will change the fuel /air ratio to something like 12:1 ( which is my target) this will use alot more gasoline but the bike will run alot cooler in the hot summer !
I had a flat spot on the XR650L just above idle but that was due to a too small of a slow speed jet anything above 3,000 RPM was perfect lean but perfect ,.... no flat spots in acceleration just one coming off idle.. it had a 50 slow speed jet in it and I put a 55 in it's place and re adjusted the fuel air screw.... the hesitation coming off idle is now gone....
....
Yes in some cases shimming works great, but I have never found an instance where it helped me...... EVER !
.....
my opinion, take it for what it's worth ! ....I never shim the needles ! LOL
....

it has been argued that shimming the needle is the same as changing the main jet but I disagree because it changes the fuel air ratio not the volume of fuel going into the engine, there is a Suttle difference. (6 of one half a dozen of another right? ) it still changes the amount of fuel going into the engine so what ever trips your trigger !!!!!

Bob.....

April 23rd, 2023, 01:37 PM	#38
Bob KellyIII Retired motorcycle Mc. Name: Robert Location: Weed, California. Join Date: Jul 2021 Motorcycle(s): 2012 Kawasaki Ninja 250R, 2021 CSC TT250, 1977 Triumph Bonneville 750cc,2001 Honda XR650L. Posts: A lot.	Jim: needle shims means the carbs have to come out.... getting the carbs out on that bike is Not EASY ! it's only easy if the carbs are already OUT.... LOL !!!!! .... Needle shims have never worked for me... they introduce a flat spot in almost every case when I have tried to use a shim... you mess with the fuel to air ratio when you Shim it changing it from 14:1 to 12:1 or some thing like that and that is not a good idea to do. changing the Main jet is by far better if you want to get more or less fuel in it. because it will increase or decrease the voluum but keep the fuel /air ratio the same. in almost every case a flat spot in the throttle opening is due to something else and not the jet needle. they put alot of time and effort to keep the fuel /air ratio correct throughout the RPM Range so the stock carb is usually spot on.... BUT it may well be spot on in a very lean or Rich way throughout the span of RPM and this is not uncommon at all especially with mods to intake and exhaust systems on the bike. if it comes to the point of shimming a needle I have to think something else is very wrong in the system.... it is designed to put out 14:1 fuel air ratio throughout the RPM range and that is a very hard trick to accomplish.... changing the main jet changes that 14:1 ratio through the entire range.... a larger main jet will lower the ratio from like 14:1 to 12:1 and a smaller main jet will increase it like from 14:1 to 16:1.... so In Most cases there is never a need to change the main jet at all... but when changes are made then adjustments have to be made.... for instance: on my XR650L I have been trying to get the Fuel/air ratio Down because it runs very lean for a air cooled bike it needs a richer mixture to help cool the air cooled engine... so I have increased the main jet size from 150 to 160 and it only changed it a little I may need to go more to something like 165 this will change the fuel /air ratio to something like 12:1 ( which is my target) this will use alot more gasoline but the bike will run alot cooler in the hot summer ! I had a flat spot on the XR650L just above idle but that was due to a too small of a slow speed jet anything above 3,000 RPM was perfect lean but perfect ,.... no flat spots in acceleration just one coming off idle.. it had a 50 slow speed jet in it and I put a 55 in it's place and re adjusted the fuel air screw.... the hesitation coming off idle is now gone.... .... Yes in some cases shimming works great, but I have never found an instance where it helped me...... EVER ! ..... my opinion, take it for what it's worth ! ....I never shim the needles ! LOL .... it has been argued that shimming the needle is the same as changing the main jet but I disagree because it changes the fuel air ratio not the volume of fuel going into the engine, there is a Suttle difference. (6 of one half a dozen of another right? ) it still changes the amount of fuel going into the engine so what ever trips your trigger !!!!! Bob..... __________________________________________________ Its too late when you've gone too far ! Last futzed with by Bob KellyIII; April 23rd, 2023 at 04:05 PM.