midrange performance problem
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Stage III
Joined: Aug 2011
Posts: 3
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From: Rapid City, SD
midrange performance problem
Ok, I am working on an 86 sportster 883 that has been bored and stroked, straight pipes, keihen buterfly carb, 155 main jet, 66 pilot jet. The problem I'm having is that at about 1/3 throtle it starts cuting out, back fire through the carb, uses lots of gas, also fuel spray out of the carb when i'm running during the back fire. It always has been very rich but recently its gotten to the point that mid range is out of the question. ive been through the carb twice, no change. any advice would be awesome. my next move will be cylinder leak down, compression test, I'll post results soon. HELP!!!
Cruiser
Joined: Mar 2014
Posts: 125
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From: michigan
Just realized this was an old thread. So if you are having the problem the original poster had, drop the bowl and make sure there is a rubber plug over the idle jet. If not, you need one. Just get a rebuild kit and it will have one.
Last edited by amasoniii; Apr 15, 2014 at 09:11 PM.
Cruiser
Joined: Mar 2014
Posts: 125
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From: michigan
Most people will tell you to get rid of the butterfly keihin, but i won't. Mine starts and runs better than most factory CV's i've seen.
A couple of tips i got from an old easy rider article to get it tuned are 1) install a screw into the hole of the tab that operates the accelerator pump so you can adjust how much it works (especially needed if you install an andrews accelerator pump and drill the extra feed hole), 2) make sure the rod for the accelerator pump is flush with the carb body when the throttle is completly closed.
An additional thing i did on mine is increase the spring pressure on the choke butterfly to make sure it doesn't vibrate when open. You just have to loop the spring around one more time. Finally, just make sure you have no carb mounting or intake leaks.
Your symptoms point to that plug being left out though.
A couple of tips i got from an old easy rider article to get it tuned are 1) install a screw into the hole of the tab that operates the accelerator pump so you can adjust how much it works (especially needed if you install an andrews accelerator pump and drill the extra feed hole), 2) make sure the rod for the accelerator pump is flush with the carb body when the throttle is completly closed.
An additional thing i did on mine is increase the spring pressure on the choke butterfly to make sure it doesn't vibrate when open. You just have to loop the spring around one more time. Finally, just make sure you have no carb mounting or intake leaks.
Your symptoms point to that plug being left out though.
Cruiser
Joined: Mar 2014
Posts: 125
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From: michigan
Oh, left one tip out, make sure the jet for the accelerator pump shoots the gas directly into the center of the butterfly or manifold. You can turn it with a wrench when you have the bowl off. Usually it comes from the factory shooting more toward the rear cylinder.
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Joined: Dec 2007
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With 1 3/4" straight pipes on an EVO XL, tremendous reversion is occuring.
3" from the end on the pipe, drill a clearence hole for a 1 1/2" long, 5/16" bolt, and simply stack 3-4 3/8" nuts on it, then nut it.
You will IMMEDIATELY notice a large torque increase, and NOW, tuning can begin, now that the pipe is attempting to work.
Scott
3" from the end on the pipe, drill a clearence hole for a 1 1/2" long, 5/16" bolt, and simply stack 3-4 3/8" nuts on it, then nut it.
You will IMMEDIATELY notice a large torque increase, and NOW, tuning can begin, now that the pipe is attempting to work.
Scott
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