Misfire

I have a problem.

My 2002 FXDL has an intermittent misfire/carb cough resulting in jerking momentary loss of power under light acceleration through all speed ranges and gears.
Specific conditions:
Reduce throttle a little to coast, then reapply minimal or more throttle to resume speed or accelerate and the engine has a single misfire and falters as a result.

This happens often during the first 20 minutes of riding then, when warmed up happens much less frequently.
Seems to happen more when rpm is reducing around the 2100 mark and throttle is reopened.
Seems to happen more during cool damp weather. Less during 33C(85F) hot weather.
Happens with 87 or 92 octane gas.
Gas tank can be full or on reserve, no difference.
More likely to occur after 10 seconds of coasting rather than 2 secs.
Warm up procedure is:
Fuel enrich full out to start, then idle for 30 secs, fuel enrich to half out to begin driving. Then fuel enrich full in after 10 minutes of driving.

The only thing that prevents the problem is to run with fuel enrich out half or full all the time. It never happens with enrich pulled half or full out.

To my knowledge bike has Stage 1 air cleaner. Unsure of carb jets, but appears to have original undamaged brass phillips head screws holding bowl together, so I assume jets are stock.
Santee 2 into 1 header with a stock FXDL muffler no baffle.
Bike purchased in Florida. Now operating in Vancouver, BC.

Things I have checked:
Idle mixture screw was 2 1/4 out. Changed to as much as 3 3/4 out. Now back to 2 1/2.
Intake leak using propane gas around the manifold.
Spark plugs changed to new correctly gapped. Dealer said they are "burning clean".
Wires appear to be good.
Recently had new stator installed and electrical system checked.
Problem still exists.

The misfire or whatever it is has a snapping/coughing sound unlike a popping from an exhaust pipe. It seems to be near the carburetor and the bike jerks back when it happens like a loss of power when the cylinder doesn't fire.

Again the only way to prevent it is to run with the enricher knob half or full out all the time. After a 6 hour ride with the enricher full in/closed it is less frequent but may still occur as described above. This leads me to believe it is a fuel problem.
I am handy enough to tackle a carb disassembly but only with some certainty it is the source of the problem, ie foreign particles clogging things up or rejetting.

Any ideas on the source of the problem would be appreciated.

FLDL02

Check your accelerator pump nozzle for a good squirt of fuel when you twist the throttle,if no squirt or very little the accel pump diaphragm needs replacing...if you do get fuel through the nozzle,I'd say your needle jet needs to be shimmed or replaced with a different tapered one...good luck,let us know what you find

Thanks Lucifer,

I get a good squirt. Dealer tech suspected a hole in diaphragm or clogged low speed jet.
Would a low speed jet have such a specific effect?
Bike starts and idles good, runs well overall, but just has that occasional misfire after rolling the throttle off slightly then back on. Does not miss any other time and never if the enricher is pulled out to 1/2 or full.
If I start the cold bike and try to ride immediately with the enricher pushed in the engine struggles to accelerate and will missfire and sputter. Just a cold engine, right? So riding 10 minutes with enricher half out until warm and bike runs fine. But after I push the knob back in the misfires come again occasionally even when bike is hot.

Also, just noticed fuel seeping from the bottom of the petcock shut off valve. This is new today. I don't believe they are related.

Thoughts?

Wouldn't hurt to check the pilot jet,possibility there...if you had a hole in the diaphragm, the slide wouldn't open when you hit the throttle...the check for that is to lift the slide and listen for air being pushed out or sucked back in when you let it go(CRS)....another is with the engine running and you goose the throttle it should lift...

They will spit and sputter when they're cold....normal....Those dang vacuum operated petcocks can effect fuel delivery if they start acting up,usually in the reduced/no flow manner....

It's the rubber diaphragm valve. If cracked, it allows additional air to mix in the accel. pump causing intermitent popping, especially when cold.

If you are using fuel with 10+% ethanol, the alchohol becomes a solvent that is very hard on rubber parts, and some metals in the fuel system. We're all stuck having to use it here, but a fuel conditioner(Sea Foam or StarTron) fixes this problem.

It's a carburator problem. Possibly a clogged pilot jet or a vacuum leak at the intake manifold. I have a similar problem and I'm switching from a 46 to a 48 pilot jet as I've not found the problem elsewhere.

So I pulled the jets, 190 and 48. Stock are 190 and 45. Switched to a 195 after discussion with Harley tech. Problem still there after a short ride. I will ride longer tomorrow to double check.
Carb bowl was pretty clean(no varnish or goo or debris).
Both jets appeared to the naked eye clean and undamaged.
Accelerator diaphragm looked intact. Good squirt when throttle opens (with bike not running).
Checked the intake manifold before with propane, will try again tomorrow.

The engine will only missfire when I roll the throttle off while cruising around 2500 rpm then smoothly roll it back on. Then rpm starts a momentary increase then "cough" once and accelerates fine. But only if choke is full in/off.
This tells me that the transition from idle throttle position to 1/4 to 1/3 open throttle after a short coast is where the fuel/air problem happens. Could an intake or other vacuum leak manifest itself this way? The jets don't seem to be clogged or damaged.
If the intake checks out I think my next step is dealership diagnosis as costly as that will be.
Thanks for everyone's input. I will let you know when it's solved.

Replaced the leaky pet-**** today, and checked intake for leaks with propane torch. No leaks detected(doesn't mean there isn't one). Replaced the 190 jet and going to ride tomorrow one last time before I pull the carb for a bath at the dealer. I am starting to think alex the dog may be on the right track with the accelerato pump. The miss only happens when rolling throttle on again after rolling it off. Even though I get a good squirt when I roll it on with the air cleaner and bike off, maybe there are times while riding that it doesn't squirt well. Manual says a hesitation on acceleration may indicate an accelerator pump problem. When cold it does hesitate and miss. When warmed up it just misses. I will have the HD techs check it out when they bench clean the carb.

I wouldn't run with the enrichener open; fuel washes the cylinder walls.

Run the A/F screw all the way in; if the engine doesn't stumble or die, the pilot jet is too large. If running a 48, a 46 might solve the problem. The below chart may help isolate the problem; note the importance of the needle. Don't get hung up on how many turns out for the A/F screw, you have to give the engine what it wants; it might be happy at 1.5 turns out or 3.5 turns out.

I agree,with a 48 pilot,it could be a too fat burp you're experiencing....nice chart djl....

Not meaning to hijack the thread, but I'm having a similar issue with my carb. I have the air/fuel screw turned out 1 1/2 turns with the CV tuners kit (46 pilot). Maybe I should turn it out more . . . ?

All the parts in the carb have about 3000 miles on them and I just recently took it apart for cleaning and inspection and everything looked good. The coughing started several hundred miles ago.

Yep...find where it idles best between 1.5 and 3.5 turns out....2.5 turns out is usually the starting point...

OK, just rode 180 miles today with the 190 and 48 jets. Decided to try to tune the cough out with the idle mixture screw. Had a lot of success.
Started by closing it until the engine stumbled, 1/2 turn open. Opened to 3/4 and adjusted idle to 1100 rpm. Drove a while still coughed. Stopped and open idle mix screw 1/4 turn. Drove some more and repeated steps until idle mixture screw is 1 1/3 open and idle set at 1100 rpm. Cough is almost impossible to induce now. Also no deceleration pop except when coasting down a steep hill that drives the engine. I won't underestimate the fine tuning adjustments of that idle mixture screw again. 1/4 turns matter.
Bike is running very smooth now. Thanks DJL for your posts that got me on the right track to tuning this thing out. I'm not sure it's cured but I will keep checking it the next few rides to be sure. Then my rides can be about pleasure instead of diagnosis.

Glad to hear the situation is improving; sounds like you are getting the process down. You will find that 1/8 turn can make a difference.

Next step is working on mileage; the needle is the main player. The pilot is right so the needle taper and position are now in play. The Yost needles I use can affect mileage 3-4mpg by lowering or raising one notch. You could experiement with a set of OEM needles to find the one that works best, or you could try a set of Yost needles. Once that is sorted out, you can move on to check the main. Time consuming but better than $300 and dyno time.

Once you have things sorted out, put the bike on a dyno and do a couple of pulls watching the AFR. The rear cylinder will always run a bit leaner than the front; a carb is a compromise. However, you can see the AFR and make any adjustments from there. It only takes a couple of pulls, less than 20 minutes, if you want to check your work. Good luck.