Thunder Jet
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Road Master
Joined: Jul 2008
Posts: 859
Likes: 416
From: In the mountains
Thunder Jet
Not sure if this belongs here or in the tuning section.
I have a 113" Ultima motor with the R1 carb (S&S G clone). Only time it ran good, start easy, no decel pop, was with AFR in the 10.5-1 range. After dyno tuning with AFR in a acceptable range, starts hard, lean up top, and a lot of annoying decel pop. I'm told the R1 is a POS, and to get a real G. I had a S&S 100" Evo with a G that ran very well, years ago. Should I try a Thunder Jet on the R1, or waste of time with that carb? If I do get a S&S G, should I have a Thunder Jet installed on it?
P. S. Not going with a Mikuni.
I have a 113" Ultima motor with the R1 carb (S&S G clone). Only time it ran good, start easy, no decel pop, was with AFR in the 10.5-1 range. After dyno tuning with AFR in a acceptable range, starts hard, lean up top, and a lot of annoying decel pop. I'm told the R1 is a POS, and to get a real G. I had a S&S 100" Evo with a G that ran very well, years ago. Should I try a Thunder Jet on the R1, or waste of time with that carb? If I do get a S&S G, should I have a Thunder Jet installed on it?
P. S. Not going with a Mikuni.
What's the AFR graph on the dyno chart look like?
If you're getting symptoms that look like a lean condition, but the dyno chart doesn't show it, that's a head scratcher.
Intake and exhaust seals check out?
If you're getting symptoms that look like a lean condition, but the dyno chart doesn't show it, that's a head scratcher.
Intake and exhaust seals check out?
Dirt don't hurt
Joined: Jan 2011
Posts: 21,065
Likes: 4,561
From: Haslet Texas
Not sure if this belongs here or in the tuning section.
I have a 113" Ultima motor with the R1 carb (S&S G clone). Only time it ran good, start easy, no decel pop, was with AFR in the 10.5-1 range. After dyno tuning with AFR in a acceptable range, starts hard, lean up top, and a lot of annoying decel pop. I'm told the R1 is a POS, and to get a real G. I had a S&S 100" Evo with a G that ran very well, years ago. Should I try a Thunder Jet on the R1, or waste of time with that carb? If I do get a S&S G, should I have a Thunder Jet installed on it?
P. S. Not going with a Mikuni.
I have a 113" Ultima motor with the R1 carb (S&S G clone). Only time it ran good, start easy, no decel pop, was with AFR in the 10.5-1 range. After dyno tuning with AFR in a acceptable range, starts hard, lean up top, and a lot of annoying decel pop. I'm told the R1 is a POS, and to get a real G. I had a S&S 100" Evo with a G that ran very well, years ago. Should I try a Thunder Jet on the R1, or waste of time with that carb? If I do get a S&S G, should I have a Thunder Jet installed on it?
P. S. Not going with a Mikuni.
Seasoned HDF Member
Joined: Aug 2008
Posts: 5,079
Likes: 2,151
From: Ohio
Can assure you a R1 isn't a POS, I'm pushing quit a bit more engine than your talking and the R1 runs flawless, it's tuned wrong.
Common AFR's on 90hp to 100hp engine is 13.2 wide open throttle, 13.8-14.0 running down the road(cruise) and 14.0 idle. The bigger cubes like 12.5 -12.8 wot, 13.2 going down the road and these numbers are detonation control because they can eat fuel, slight over fueling doesn't seen to bother them, Idle is afr that works.
If your running 10.5 cruise and 10.5 wot is past the slightly rich mark but shouldn't have anything to do with idle and your area of problem from the post. I mentioned what works at idle and a suggestion coming, the engine does need to run rich at idle like 12.5 because with the bigger open exhausts needed for big cubes pull a lot of air back through exhaust into the cylinders (reversion) when the throttle is shut off slowing down leaning out the fuel mixture and takes a while to recover.
If your wot and cruising runability is good then tune your idle to 1500 rpms with the air mixture screw and not worry about afr's, start turning it until the pop and spits go away while slowing down or taking off, if it's out of turns go a bigger size up on the low jet and start over. A carb has problems in the crossover area on big cubes, what needs to be done is mask lower crossover between low jet and air screw with rich fuel to cover the air (reversion) being pulled backward from big exhaust, large engine bore, it's tendency is going lean - exhaust gurgle - pop out the carb. Run it coming to stops and richen by the needle until the de-accell pop is gone
Common AFR's on 90hp to 100hp engine is 13.2 wide open throttle, 13.8-14.0 running down the road(cruise) and 14.0 idle. The bigger cubes like 12.5 -12.8 wot, 13.2 going down the road and these numbers are detonation control because they can eat fuel, slight over fueling doesn't seen to bother them, Idle is afr that works.
If your running 10.5 cruise and 10.5 wot is past the slightly rich mark but shouldn't have anything to do with idle and your area of problem from the post. I mentioned what works at idle and a suggestion coming, the engine does need to run rich at idle like 12.5 because with the bigger open exhausts needed for big cubes pull a lot of air back through exhaust into the cylinders (reversion) when the throttle is shut off slowing down leaning out the fuel mixture and takes a while to recover.
If your wot and cruising runability is good then tune your idle to 1500 rpms with the air mixture screw and not worry about afr's, start turning it until the pop and spits go away while slowing down or taking off, if it's out of turns go a bigger size up on the low jet and start over. A carb has problems in the crossover area on big cubes, what needs to be done is mask lower crossover between low jet and air screw with rich fuel to cover the air (reversion) being pulled backward from big exhaust, large engine bore, it's tendency is going lean - exhaust gurgle - pop out the carb. Run it coming to stops and richen by the needle until the de-accell pop is gone
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Road Master
Joined: Jul 2008
Posts: 859
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From: In the mountains
Plugs looked a little sooty when it ran good. Mileage was terrible running the 2 lane roads at 55 mph. Lucky to get 29 miles per gallon.
1997 Bagger what do you mean by tuning idle to 1500 rpm's?
1997 Bagger what do you mean by tuning idle to 1500 rpm's?
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Seasoned HDF Member
Joined: Mar 2010
Posts: 21,093
Likes: 7,619
From: Poolville
What AFR Meter do you have and can you down load a data log.. what jets were you running when it ran good and what jets are you currently running that's creating the decel pop? Installing a T-jet is always a good thing on the bigger motors, 3 jets can really help you to smooth out the transition points that can cause a lean or rich condition...
Club Member
Joined: Mar 2009
Posts: 66,114
Likes: 51,401
From: Niles Canyon Ca.
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.