I have a '97 Heritage FLSTC that I recently purchased. It has the 1340 EVO with stock carb, K&N filter, and new Andrews 220 Cam and lifters/rods.

I didn't bother checking the plugs right away as I've only had it a few weeks and only put about 70 miles on it. I changed the oil, some small bolt on parts like switch housing, adjusted the clutch, replaced timer cover.

The problem:

Went out to fire it up today for a ride, and it sounded awful and backfired. I felt the pipes and engine and only the front cylinder was firing/getting warm. I pulled the plugs and they were both black and a little wet.

I cleaned the plugs off, sanded the contact points with some fine sandpaper, checked the gap ( .040) and reinstalled. Both cylinders were firing now, but it still sputtered a little and popped. After 1 minute of running, the plugs were fouled again and wet.

Did I do something wrong?

Thanks for any help.

 

Do a Compression Check.. That looks good, look for Carb problems..

 

don't have the tools or skill to do that myself, but how could that have happened overnight?

 

I would check switch housing for pinched wire or bare wire ,sounds like a wire is shorting out.

 

The above seems unlikey
A black plug is sign of a rich engine.Often this is caused by the engine starting and the choke being on.
If it persists the most obvious problem is that the plugs or leads are loose. Check the leads at the coil if they are in tight check the plugs are in the caps properly and the tops are screwed on tightly. If this is ok buy some new plugs and replace them. If this does not cure the problem check if the plugs are wet with petrol or oil.If its petrol and the plug is sooty this is most likely a carb problem , could be a faulty choke mechanism. If the black is oil it is most likey valve problems like a leaky valve seal or that a piston ring has gone.When the engine is running check for smoke from the exhaust.If the smoke is coming out at idle it is likely a valve seal. On an EVO these are rubber and can go brittle especially of the bike has been stood for a period of time.If the engine smokes when you are running the bike and have shut the throttle off it is likely piston rings. In answer to your question none of these would be your fault but may (but I don't know) be areason some one would sell it. EVO's are good bikes and repairable. If you are stuck take it to a reliable mechanic, avoid a Harley dealer unless you are rich!!! good luck let us know the problem mwhen fixed.

 

Have same year & model and could write a book on them with all that has gone wrong! I'd watch checking engine operation by hand: could have memorable results! Is this bike stored inside? Had a bit of rain here over the weekend which could have gotten water in somewhere causing a temporary, "only while wet" bug like in the RUN/STOP switch, for example. Check for moisture in the "timer cover", too: my Sportster has same indications after washings I need to seal up with rubber sealant but been working on a '85 of friend. S/P gap is .038 to .040" so W/I spec. I wouldn't be tearing the motor apart looking for leaking valve seals just yet (not without compression & leakdown test at least) or breaking down the carb as these problems "usually" appear gradually not just BANG: it's bad! but myself not knowing or tools to do and looking for quick fix at low cost: buy a new set of plug wires and plugs. At least you know you have new plugs and wires and how old they are. Does it do it still? I go with the electrical side since it came on so suddenly (and wet, unburned gas in cylinders) vice carb (which does cause same issues). Here's a few things to check for easy to do:

*If “engine cranks but does not start”, check module connection under crankcase and perform "Test #5: LED Flash". Check ignition coil hook-ups (Test #2 & 3). Turn ignition on/off to save battery voltage while performing these tests!

1. BATTERY VOLTAGE WITH KEY ON___________VDC ("lights on" BATTERY VOLTAGE)
MULTIMETER LEADS TO BATTERY TERMINALS RECORD VALUE {13-14.7 VDC usual}
Verifies battery voltage

2. POWER TO COIL________VDC (BATTERY VOLTAGE)
REMOVE W/BLK WIRE TO RIGHT-SIDE OF COIL RED LEAD TO W/BLK WIRE BLK LEAD TO GROUND RECORD VALUE
Checks power to primary coil side.

3. POWER FROM COIL_______VDC (BATTERY VOLTAGE)
RED LEAD TO PINK WIRE TO LEFT-SIDE OF COIL BLK LEAD TO GROUND RECORD VALUE
Checks secondary coil power out.

3A. COIL/WIRE RESISTANCE: PRIMARY 2.5-3.1 OHMS
SECONDARY 10,000-12,500 OHMS
SPARK WIRES=250-583 OHMS per inch
Checks coil & wire condition.

4. FLASH TEST: SPARK? YES NO (Need tester as in Chapter 8-4 of service manual!)
USING COIL TESTER BLK ALIGATOR TO PINK COIL WIRE O/W ALLIGATOR TO GROUND TOUCH ORANGE PROBE TO BLACK ALLIGATOR OBSERVE SPARK
Checks for active, timed spark to cylinder from coil.

5. LED FLASH TEST: FLASHING? YES NO
WITH RUNNING BIKE, OBSERVE RED LED FLASHING ON MODULE
If the module is NOT flashing, there is no power going to the module itself or bad module.

These are not "end all, be all, tests but will eliminate certain problems you describe. Probably just need the new wires and/or plugs though!

 

Sorry, #5 is at the cam position sensor in the right side (or "timing cover"). Manual would help but remove plates only (do not loosen screws holding module as this sets the timing! F this up = bad ju-ju!) and observe LED on module with engine running {brightly flashing} or cranking {flickering somewhat dully but illuminating}.

 

great stuff! Looks like I better get intimate with my multimeter! Thanks! I'll let you know what I find.

 

Ok, couldn't make it down to buy new plugs and wires today, but here is what I did and what happened.

1. Loosened throttle housing and made sure no wires were pinched, retightend.
2. Cleaned spark plugs and wires and reconnected.
3. Removed timing cover to observe.
4. Started with choke pulled out for about 10 seconds then kept it running with throttle until it would idle by iteself. Popping/backfiring with occasional flame out the back of the pipe.
5. Adjusted idle till it sounded "right". Not too low/loping sound, but not racing either.
6. Checked the timing hole, but could not see any light, just the turning wheel in the window. Put the timing cover back on and let idle for about 4 min with occasional throttle bursts.
7. Took for a short ride, about 5 miles. It would backfire under hard throttle, but engine seemed pretty smooth. After a couple stop signs, I had to give it some "extra" throttle from full stop. It sound like it was bogging down if I tried to smooth throttle off the line.
8. Got home, shut it off, and after about 3 min, fired it up again and it started with no choke and smooth idle.

??????????????????????

 

Throw the old plugs away, then install new plugs.
and fix the carb