04 FXSTS Carb Jetting Recomendation
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Joined: Jan 2021
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From: Montreal
04 FXSTS Carb Jetting Recomendation
hello folks,
need some advise. I am currently rebuilding my carb and when i pulled out main jet (190 size) and slow jet (48 size). only mods i have are a stage 1 air intake and some V&H short shots. Everything else is pretty much stock.
shouldn't by jets be 185 & 45? Bike, according to me, runs fine with the existing settings, (i am no expert...) but wondering if that's too much for a relatively stock bike.
not sure if there is a correlation here, but the only issue i had as of late is occasionally when i twist the throttle, i would get a skip (or a hesitation) almost like the bike wanted to suffocate... is this a result of letting in too much (or too little) air/fuel mix?
appreciate the help.
need some advise. I am currently rebuilding my carb and when i pulled out main jet (190 size) and slow jet (48 size). only mods i have are a stage 1 air intake and some V&H short shots. Everything else is pretty much stock.
shouldn't by jets be 185 & 45? Bike, according to me, runs fine with the existing settings, (i am no expert...) but wondering if that's too much for a relatively stock bike.
not sure if there is a correlation here, but the only issue i had as of late is occasionally when i twist the throttle, i would get a skip (or a hesitation) almost like the bike wanted to suffocate... is this a result of letting in too much (or too little) air/fuel mix?
appreciate the help.
Seasoned HDF Member
Joined: Sep 2008
Posts: 14,156
Likes: 11,244
From: San Diego, CA
I'm going to assume you still have the OEM CV40 carb. I believe it was a very underrated carb. When they went to the constant velocity Keihin carb (CV40) in 1989, there were many years of bad stories about the previous butterfly valve, Keihin carbs... After many years of replacing the butterfly carbs with Mikuni, S&S, and I even put an SUII carb on my shovel head, I don't think people gave the CV40 a fair shot before jumping on the "Replace that Keihin carb with a (insert your favorite carb here)..!" bandwagon....
The problem you are experiencing could be several things.... since you are rebuilding it, tune it right and get it dialed in...
Has the EPA plug been removed from your mixture screw.....???
Many people, on a stage I would leave the mixture screw plug in place, and just bump up the pilot jet from 45 to 48... it can work, but not optimal...
My '02 FXSTS, is an 88" w/Stage I... SE high flow air filter and V&H Straight Shots dual exhaust.
I'm running the 45/190 jets, CV Performance velocity needle, and about 2 turns on the mixture screw..... mine runs flawlessly, and fires right up when warm, or cold with the enricher pulled out 3/4... but every bike is a little bit different... One thing I learned with playing around with EFI tunes is that same bike, same year, same mods, will have different VE tables that will affect the tune in different areas...
I suggest doing a basic carb tune, starting with the mixture screw, and let how the bike responds tell you what you need in the way of jets/needle...
Go to CV Performance and they have many tutorials about your carb... that is if you still have the OEM CV40 carb...
https://cv-performance.com/instructions-guides
Good luck with your carb tuning...
The problem you are experiencing could be several things.... since you are rebuilding it, tune it right and get it dialed in...
Has the EPA plug been removed from your mixture screw.....???
Many people, on a stage I would leave the mixture screw plug in place, and just bump up the pilot jet from 45 to 48... it can work, but not optimal...
My '02 FXSTS, is an 88" w/Stage I... SE high flow air filter and V&H Straight Shots dual exhaust.
I'm running the 45/190 jets, CV Performance velocity needle, and about 2 turns on the mixture screw..... mine runs flawlessly, and fires right up when warm, or cold with the enricher pulled out 3/4... but every bike is a little bit different... One thing I learned with playing around with EFI tunes is that same bike, same year, same mods, will have different VE tables that will affect the tune in different areas...
I suggest doing a basic carb tune, starting with the mixture screw, and let how the bike responds tell you what you need in the way of jets/needle...
Go to CV Performance and they have many tutorials about your carb... that is if you still have the OEM CV40 carb...
https://cv-performance.com/instructions-guides
Good luck with your carb tuning...
Last edited by hattitude; Jan 31, 2022 at 01:20 PM.
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Joined: Jan 2021
Posts: 93
Likes: 18
From: Montreal
That is correct oem cv Keihin carb.
yes I did drill out the stock fuel mixture screw. I purchased an All ***** carb rebuild kit with a similar adjustment screw like the one from CV.
i was thinking of backing it out 1-3/4 turns and setting it with a 190/45 jet set up and see how it goes.
additionally in removing my top of the carb I realized that the diaphragm was a little chewed up Im going to replace the vaccuum piston assembly.
hopefully will fix my problems.
Keep you posted.
yes I did drill out the stock fuel mixture screw. I purchased an All ***** carb rebuild kit with a similar adjustment screw like the one from CV.
i was thinking of backing it out 1-3/4 turns and setting it with a 190/45 jet set up and see how it goes.
additionally in removing my top of the carb I realized that the diaphragm was a little chewed up Im going to replace the vaccuum piston assembly.
hopefully will fix my problems.
Keep you posted.
Seasoned HDF Member
Joined: May 2005
Posts: 10,232
Likes: 9,320
From: Georgia
I'm going to assume you still have the OEM CV40 carb. I believe it was a very underrated carb. When they went to the constant velocity Keihin carb (CV40) in 1989, there were many years of bad stories about the previous butterfly valve, Keihin carbs... After many years of replacing the butterfly carbs with Mikuni, S&S, and I even put an SUII carb on my shovel head, I don't think people gave the CV40 a fair shot before jumping on the "Replace that Keihin carb with a (insert your favorite carb here)..!" bandwagon....
The problem you are experiencing could be several things.... since you are rebuilding it, tune it right and get it dialed in...
Has the EPA plug been removed from your mixture screw.....???
Many people, on a stage I would leave the mixture screw plug in place, and just bump up the pilot jet from 45 to 48... it can work, but not optimal...
My '02 FXSTS, is an 88" w/Stage I... SE high flow air filter and V&H Straight Shots dual exhaust.
I'm running the 45/190 jets, CV Performance velocity needle, and about 2 turns on the mixture screw..... mine runs flawlessly, and fires right up when warm, or cold with the enricher pulled out 3/4... but every bike is a little bit different... One thing I learned with playing around with EFI tunes is that same bike, same year, same mods, will have different VE tables that will affect the tune in different areas...
I suggest doing a basic carb tune, starting with the mixture screw, and let how the bike responds tell you what you need in the way of jets/needle...
Go to CV Performance and they have many tutorials about your carb... that is if you still have the OEM CV40 carb...
https://cv-performance.com/instructions-guides
Good luck with your carb tuning...
The problem you are experiencing could be several things.... since you are rebuilding it, tune it right and get it dialed in...
Has the EPA plug been removed from your mixture screw.....???
Many people, on a stage I would leave the mixture screw plug in place, and just bump up the pilot jet from 45 to 48... it can work, but not optimal...
My '02 FXSTS, is an 88" w/Stage I... SE high flow air filter and V&H Straight Shots dual exhaust.
I'm running the 45/190 jets, CV Performance velocity needle, and about 2 turns on the mixture screw..... mine runs flawlessly, and fires right up when warm, or cold with the enricher pulled out 3/4... but every bike is a little bit different... One thing I learned with playing around with EFI tunes is that same bike, same year, same mods, will have different VE tables that will affect the tune in different areas...
I suggest doing a basic carb tune, starting with the mixture screw, and let how the bike responds tell you what you need in the way of jets/needle...
Go to CV Performance and they have many tutorials about your carb... that is if you still have the OEM CV40 carb...
https://cv-performance.com/instructions-guides
Good luck with your carb tuning...
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