Thunder Jet
Seasoned HDF Member
Joined: Aug 2008
Posts: 5,080
Likes: 2,152
From: Ohio
On the bigger picture is a 31 on a 113" will be pig rich, more like a 29.5 intermediate is going to be closer instead of a 31 and if it is running 10.5 afr at wide open throttle you'll need to drop the big jet more, can't see any dyno tuner turning loose a Harley engine at 10.5 back onto the street, it's leaving horsepower on the table unless he didn't want to f*ck with a carb, it's not tuned right
Last edited by 1997bagger; Jan 18, 2020 at 09:41 PM.
Seasoned HDF Member
Joined: Aug 2008
Posts: 5,080
Likes: 2,152
From: Ohio
He adjusted your air/screw lean causing all of the problems, find another dyno tuner, this one isn't doing you justice.
Seasoned HDF Member
Joined: Jul 2014
Posts: 8,590
Likes: 3,361
From: Cental, MI
Just so you understand all a thunder jet does is help correct a lean condition in the higher RPM ranges, not much help under 4500 PRM if the carbs halfway tuned correctly. You a street racer or strip guy go for it other wise average rider sees no gain.
Oh and for what it's worth my 93" HiPo shovel with an " E " only gets 36 to 38 mpg tops if I ride like a newbie, get the happy hand going on that drop's under 30 quick.
Oh and for what it's worth my 93" HiPo shovel with an " E " only gets 36 to 38 mpg tops if I ride like a newbie, get the happy hand going on that drop's under 30 quick.
Note; If you are not adjusting the air bleed... you are Not tuning the Thunderjet-S&S
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Road Master
Joined: Jul 2008
Posts: 859
Likes: 416
From: In the mountains
Use the air/fuel idle screw to remove your problems from idle to 1500 rpms is the answer to the question. Your main problem is in the 1500 rpm and below area controlled by the air/fuel screw, it is lean and causes a intake pop, exhaust gurgle/pop and hard starts. Turn your air/fuel screw out in 1/2 turn increments until the pop goes away and stop.
On the bigger picture is a 31 on a 113" will be pig rich, more like a 29.5 intermediate is going to be closer instead of a 31 and if it is running 10.5 afr at wide open throttle you'll need to drop the big jet more, can't see any dyno tuner turning loose a Harley engine at 10.5 back onto the street, it's leaving horsepower on the table unless he didn't want to f*ck with a carb, it's not tuned right
On the bigger picture is a 31 on a 113" will be pig rich, more like a 29.5 intermediate is going to be closer instead of a 31 and if it is running 10.5 afr at wide open throttle you'll need to drop the big jet more, can't see any dyno tuner turning loose a Harley engine at 10.5 back onto the street, it's leaving horsepower on the table unless he didn't want to f*ck with a carb, it's not tuned right
Last edited by natural gasser; Feb 2, 2020 at 03:13 PM.
Seasoned HDF Member
Joined: Aug 2007
Posts: 8,198
Likes: 3,087
From: NW AR
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Seasoned HDF Member
Joined: Mar 2010
Posts: 21,093
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From: Poolville
Just so you understand all a thunder jet does is help correct a lean condition in the higher RPM ranges, not much help under 4500 PRM if the carbs halfway tuned correctly. You a street racer or strip guy go for it other wise average rider sees no gain.
Oh and for what it's worth my 93" HiPo shovel with an " E " only gets 36 to 38 mpg tops if I ride like a newbie, get the happy hand going on that drop's under 30 quick.
Oh and for what it's worth my 93" HiPo shovel with an " E " only gets 36 to 38 mpg tops if I ride like a newbie, get the happy hand going on that drop's under 30 quick.
As bagger also said, turn out your idle mixture screw and go from there..
Seasoned HDF Member
Joined: Jul 2014
Posts: 8,590
Likes: 3,361
From: Cental, MI
Twisted is absolutely correct, the thunder jet really doesn't become active till around 4200-4300 RPM. Some little sooner some a little later, it depends on the velocity of air going through the Venturi creating the lower pressure to drag the fuel up into the jet. the reason I use one is both for performance and better fuel management I have a very built 96" Evo where I can utilize that. The whole idea is to decrease the overlap of fuel creating a rich condition as the main jet transitions in and now cause a lean condition above 5000 RPM. Another words you can use a smaller main jet where it normally transitions in around 2800 RPM and not cause a rich condition at that RPM because the jet was too big. so now you only need the main jett to carry you from roughly 2800 RPM to 4200 RPM because the thunder jet will take over from there so you would definitely be running a smaller main jet if you're going to run a thunder jet.. It is a pretty good concept but you really need to know how to tune it.. As for the air bleed, its role is to allow what RPM range you want the main jet to come in at. The bigger the air bleed the later the circuit on the main jett will become active..
As bagger also said, turn out your idle mixture screw and go from there..
As bagger also said, turn out your idle mixture screw and go from there..
if you are remiss in utilizing it as a System in order to enhance the midrange with the other jets/airbleed
you have wasted time and effort even fooling with the Thunderjet
Last edited by Racepres; Feb 4, 2020 at 08:30 AM.