I have a 2000 FXDS, 39k miles, no engine or mechanical mods to speak of. It is suddenly running like crap. It starts normally and seems to idle more or less normally, but when I twist the throttle it spits and sputters, and I have no power to speak of. The bike ran fine on Saturday (around 100 miles or so), but Sunday morning full throttle in top gear got me 50 mph and 2500 rpm. I did run Seafoam in the tank on Saturday, used most of that tank up on Sunday morning. That might or might not be unrelated. It continues to run poorly with new gas (91 octane, no Ethanol)

I am fairly new at the wrenching part of this experience, so I am opening it up for suggestions. Cause and troubleshooting suggestions?

 

1) are both cylinders firing? feel if the exhaust coming out of one or the other is cold -change one or both plugs with fresh. Could also be a bad coil in this case.

2) is your MAP sensor working? If not then your ignition isn't advancing as it needs to at different engine loads and throttle... engine will act lame. You would need to check voltage output from the sensor at different vacuum, and compare with a known good one.

3) could also be a bad crank position sensor... not sure about the ones on earlier Dynas, but the rubbermount Sportys ('04 and newer) were notorious for CKP failure

 

+1 on all the above, on my 2002 I found a pinhole on the carb slide diaphragm., in the spring time due to choke use you may have fouled the plugs, try some fresh ones

 

My Road King did the same thing. It was the fuel filter.

 

So, here is what we have learned:
--->Pulstar spark plugs and Seafoam are a bad combination
---> Always try the easy stuff first. It is a constant source of amazement to me how often I have forgotten that over the years.

Anyway, now I twist the throttle and the damn thing almost jumps out from under me. Little bit of smoke in the exhaust, but I will see if that dissipates. After a week of crappy combustion, it might smoke for a few miles.

Thanks to all,