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Stumped, Need Help...Sportster Running Rough!

The bike has 15,000 miles. It is ridden regularly and I drained the tank and put fresh fuel in. There is no backfiring and all voltages check out fine. I am an HD mechanic and I've done everything I know of to do and checked everything out down to the grounds. Initially when I start it it runs smooth but within seconds it starts running rough and rich and fouls plugs. It's a nightmare!
 
Welcome to the forum, I'm sure if you went so far as to replace the ICM you've tried fresh fuel & spark plugs, is it rough running just at idle, or under load, any misfires or just rough, a little more info on what it does and when it does it might help? The compression is at the low end, but still in spec, have you checked the coil & plug wires?
 
Yes,vacuum petcock. I've eliminated fuel/carburation as the problem after changing carbs.

It is rough whether idling or under load. No missing or backfiring just rough and rich. Checked the coil and plug wires too.
 
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Would you happen to have access to a 2 gas (HC & CO) Infra-red exhaust analyzer? That would immediately tell you if it is an air/fuel ratio problem or a mechanical/ignition problem.

If not my next move would be a leakdown tester just to see where the compression is going.
 
I would try using a spark gap tester just to see what the di-electric strength of the coil was. It would give you a good idea how much spark duration you have. (available voltage minus ionization voltage=spark duration)

Do you happen to know what you spark advance is at idle. Are you using a complete HD stock ignition and coil set up with stock ignition factory curve.

Chopper said:
The compression is at the low end, but still in spec,
Click to expand...

Chopper, 120 psi is still in spec? That to me is so low. (?) I just can't see much power being developed if it has stock cams. To me a ton of unburned fuel would result. (?)
 
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sure vac petcock isnt leaking and allowing fuel down the vac line into carb..swapping carbs wouldnt matter if this is happening
 
Did you try the Crank Position Sensor? No DTC codes...had intermittant stumbling, after riding a few minutes up to 10 minutes after running fine, engine would sputter, incomplete combustion, rich mixture...that would cause engine to die and not restart. Ended up changing it AND the ignition coil (caused same problem but at high temperature longer running). Bike ran fine after that...troubleshooting this way is not fun or easy, but isn't it always the last part you changed out? :yes
 
1. I had some rough & rich running issues at idle/low speed when my VOES had broken - checked?
2. Carb icing (don't know where you are, but it can happen at above freezing temps) - I've had that too, and that gave a rough running & poor idle condition
3. Partially clogged airfilter?
4. It is of course running on both cylinders?
 
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