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Sportster Motorcycle Air intake, Carburetor, EFI, Fuel, and Exhaust Problems, advice and/or how tos for Sporster and Buell motorcycle carburators, Electronic Fuel Injection (EFI), Air Intake, Fuel and Exhaust.

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Old 4th December 2021
CaptainZoop CaptainZoop is offline
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Default Tuning a keihin butterfly

Hey guys, I'm trying to tune this keihin butterfly style carburetor on my 77 ironhead running open drag pipes and an air cleaner with a mesh insert with a 165 main jet but I am stumped at WOT. It starts fine, idle to 1/4 turn is fine, 1/4 to 3/4 turn is fine with hardly any flat spots, 3/4 to WOT pulls fine but then once I stay at WOT the bike stops accelerating and feels like it's hitting a wall then when I back off to 7/8 it slightly pulls again. I believe I'm running lean but do not have any jets at the moment as I cannot find a dealer locally. Can somebody link me to an online dealer where I can buy keihin "butterly" style main jets and NOT keihin "CV" style main jets? Please and thank you
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Old 5th December 2021
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Default

If it pulls fine until sustained high RPM, it may not be the carb.
You may be wrapping excess oil around the flywheels.
Here is some info on wet sumping at high revs.
See if any of that sounds familiar.
http://sportsterpedia.com/doku.php/t...e_to_high_revs
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Old 5th December 2021
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jets-r-us
you may be out flowing the needle and seat on the inlet or maybe the float is not set right.
i think you are lean also as too rich will cause it to blubber.
have you tried the plug chop method to see what the plugs look like?
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"When I back off to 7/8 it slightly pulls again"... you are lean.

Do a keihin butterfly search here http://www.v-twinforum.com/forums/se...archid=1442573

Last edited by Fivecats; 5th December 2021 at 21:22..
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I’m running a 170 main in my ‘83 with the Keihin carb, and it’s dialed in really well. Screaming Eagle air cleaner with a K&N filter, stock headers with Dyno-Power slip on mufflers. I’ve also removed the choke plate and shaft, and installed an Andrews high-flow accelerator pump kit in it.
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Old 12th December 2021
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So I got my hands on a 170 main jet finally and problem solved. I can now WOT on the freeway without losing power. Also worth noting, a couple of times my choke plate would close after backfiring because I removed the choke lever to use it’s slot next to the ignition for a kill-switch. This caused a lean condition and made it impossible to go above 1/2 throttle. I wired the choke closed so that it will not happen anymore (but can still use it to warm up bike). Thanks everyone for tour help/input.
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