S&S Carb Mods
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Grand HDF Member
Joined: Sep 2022
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From: Florida
S&S Carb Mods
When I Google things like S&S carb modifications or when I try and do a search here surprisingly not much comes up. There are many known modifications for S&S carburetors. Some are worthwhile in certain scenarios and others are just plain stupid and don’t work. I thought I’d start a thread and see what turns up and what people have had success with, and no success with…
For example, personally, I don’t like thunder jets. I’ve just never really seen any advantage at the dragstrip. I do believe you can see an advantage on an AFR grid…. But I’ve not seen that make a hill of beans at the dragstrip. It takes twice as long to tune and complicates the process. But just because it didn’t work for me, doesn’t mean that it hasn’t worked for others who profess that they worked for them. Things like the Yost power tube or the Holley booster just seem kind of dumb to me. But there are lots of worthwhile mods like the air bleed. Boring the Ventura..
What really preempted this thread is I was looking for quantifiable proof that shaving the throttle shaft, does increase CFM flow. I’ve done it on a number of S&S carburetors.
Currently, the S&S, G Carb that is on my 127 has the external air bleed mod, shaved Throttle shaft and is bored out. I have a spare G I’m going to set up for the 127… just wondering what gain really is there with shaving the throttle shaft? May revisit one Thunder jet with the spare.
Anyone ever put one on a flow bench to see before and after cfm?
Anyway, if you like a mod share what and why.
For example, personally, I don’t like thunder jets. I’ve just never really seen any advantage at the dragstrip. I do believe you can see an advantage on an AFR grid…. But I’ve not seen that make a hill of beans at the dragstrip. It takes twice as long to tune and complicates the process. But just because it didn’t work for me, doesn’t mean that it hasn’t worked for others who profess that they worked for them. Things like the Yost power tube or the Holley booster just seem kind of dumb to me. But there are lots of worthwhile mods like the air bleed. Boring the Ventura..
What really preempted this thread is I was looking for quantifiable proof that shaving the throttle shaft, does increase CFM flow. I’ve done it on a number of S&S carburetors.
Currently, the S&S, G Carb that is on my 127 has the external air bleed mod, shaved Throttle shaft and is bored out. I have a spare G I’m going to set up for the 127… just wondering what gain really is there with shaving the throttle shaft? May revisit one Thunder jet with the spare.
Anyone ever put one on a flow bench to see before and after cfm?
Anyway, if you like a mod share what and why.
Last edited by Rains2much; Jun 12, 2024 at 09:11 AM.
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Grand HDF Member
Joined: Sep 2022
Posts: 4,335
Likes: 3,756
From: Florida
Surprised there weren’t any replies?
Is it time marches on and nobody cares about performance with a carburetor? Or, maybe nobody ever looks at the Carb section in the forum?
Is it time marches on and nobody cares about performance with a carburetor? Or, maybe nobody ever looks at the Carb section in the forum?
Grand HDF Member
Joined: May 2014
Posts: 3,822
Likes: 1,170
From: florida
i love my S&S!
i can understand why some people have issues with the ThunderJet mod, but after a while i learned how it worked. It is MUCH easier to dial in on a dyno. the other advantage of the mod is that you can actually dial in the mid good enough to actually get decent fuel mileage!! might not matter to everyone, but when you've got a big inch Sporty with a small fuel tank, mpg counts!
the external air bleed is also great, and also part of the T Jet mod.
most people tried to used the T Jet as a band aid for a bad part combination, and there is some success with that, but when you've got a good combo it can really shine!
As to your question on the shaved throttle shaft,,,,do you know anyone with a flowbench? if so get together with them and actually test your mod and see what you get.
i've tried the other mods mentioned, and none of them really produced any positive results on the real dyno or the but dyno. both the yost tube and that wierd holly thing didn't do squat!!
just my 2 cents.
m
i can understand why some people have issues with the ThunderJet mod, but after a while i learned how it worked. It is MUCH easier to dial in on a dyno. the other advantage of the mod is that you can actually dial in the mid good enough to actually get decent fuel mileage!! might not matter to everyone, but when you've got a big inch Sporty with a small fuel tank, mpg counts!
the external air bleed is also great, and also part of the T Jet mod.
most people tried to used the T Jet as a band aid for a bad part combination, and there is some success with that, but when you've got a good combo it can really shine!
As to your question on the shaved throttle shaft,,,,do you know anyone with a flowbench? if so get together with them and actually test your mod and see what you get.
i've tried the other mods mentioned, and none of them really produced any positive results on the real dyno or the but dyno. both the yost tube and that wierd holly thing didn't do squat!!
just my 2 cents.
m
Thread Starter
|
Grand HDF Member
Joined: Sep 2022
Posts: 4,335
Likes: 3,756
From: Florida
i love my S&S!
i can understand why some people have issues with the ThunderJet mod, but after a while i learned how it worked. It is MUCH easier to dial in on a dyno. the other advantage of the mod is that you can actually dial in the mid good enough to actually get decent fuel mileage!! might not matter to everyone, but when you've got a big inch Sporty with a small fuel tank, mpg counts!
the external air bleed is also great, and also part of the T Jet mod.
most people tried to used the T Jet as a band aid for a bad part combination, and there is some success with that, but when you've got a good combo it can really shine!
As to your question on the shaved throttle shaft,,,,do you know anyone with a flowbench? if so get together with them and actually test your mod and see what you get.
i've tried the other mods mentioned, and none of them really produced any positive results on the real dyno or the but dyno. both the yost tube and that wierd holly thing didn't do squat!!
just my 2 cents.
m
i can understand why some people have issues with the ThunderJet mod, but after a while i learned how it worked. It is MUCH easier to dial in on a dyno. the other advantage of the mod is that you can actually dial in the mid good enough to actually get decent fuel mileage!! might not matter to everyone, but when you've got a big inch Sporty with a small fuel tank, mpg counts!
the external air bleed is also great, and also part of the T Jet mod.
most people tried to used the T Jet as a band aid for a bad part combination, and there is some success with that, but when you've got a good combo it can really shine!
As to your question on the shaved throttle shaft,,,,do you know anyone with a flowbench? if so get together with them and actually test your mod and see what you get.
i've tried the other mods mentioned, and none of them really produced any positive results on the real dyno or the but dyno. both the yost tube and that wierd holly thing didn't do squat!!
just my 2 cents.
m
To get 11s out of a street ridden Shovelhead with pump gas, stock heads and cases, no shift assistance and a 130 tire means your running the right combination of parts. The part that as wrong in that scenario was the thunder jet. So distilled down.. it didnt work for me then.
Some context.. this was late 90s early 2000s and mostly hot street & Vintage Street class, so these bikes were under 98 and pump gas due to rules. Maybe my experience with Thunder jets will be different if I try again with much larger engines.
Currently Im thinking of adding 1 Thunder jet to my bored out spare.. It seems logical that 127 will be harder to consistently feed with just two fuel circuits. Max Headflo shared that you can play with the air bleed thats inside the thunder jet and better tune when it comes in might be worth a try.
Road Warrior
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Road Master
Joined: May 2018
Posts: 778
Likes: 178
From: Bay Area
I had the Ultima version of the G on a 131 and could never get it dialed in right, always had a flat spot or other issues. Changed it up to a real S&S G that I had Scott at hillside work over for me and most of the issues were resolved. While the 131 does run well I will say the Mikuni 45 I have on my 111 is much easier to work with and fine tune. If the Mikuni 48 wasnt such a dam cinder block of a carb I might entertain putting one on the 131 but Its just too big in overall size and ironically probably too small internally lol
The thunderjet was a must for me to smooth out the transition between jets. Maybe its not needed for a drag strip where you are wide open in which case just run a Super B, but for big motors to have nice street manors I dont know of another way..
The thunderjet was a must for me to smooth out the transition between jets. Maybe its not needed for a drag strip where you are wide open in which case just run a Super B, but for big motors to have nice street manors I dont know of another way..
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