So here are spark plugs, brand new, just letting the bike idle for about 4 minutes total. Then giving 1/2-3/4 throttle for about 5 seconds, and then kill the engine.
I have went from stock pipes with kuryakyn air cleaner that running rich (according to plugs and gas mileage) with a 45 pilot and a 175 main. I put VH shorts and Arlen ness big sucker 2. Found an intake leak so Ive replaced the warped flanges, and pinched intake gaskets. Carb has been rebuilt with the James kit. Heres my jetting progression and results of each

45/175 sneezing
46/175. sneezing still
46/180+shim needle- back fire central
45/180 no shim. Back to sneezing at wide throttle
45/170 no shim. No sneeze, no backfire, no decel pop, just pitch black plugs in 5 mins of idle.


I am at my Wit's End I have no idea where to go now

 

First, your method of running the engine to check plugs is very flawed. Are you really going to more than 1/2 throttle for 5 seconds in neutral?? Don’t do that!!!
Start with new plugs.
Ride the bike until warmed up. Run the engine under load at full throttle (preferably up a long hill) and immediately shut the engine off. Check plugs. Adjust main jet accordingly. Ride the bike normally and stop and adjust idle air screw with the engine at a slow idle. if you have to turn it out more than 3 turns, increase slow jet size. If you can turn it all the way in, decrease the size. Adjust needle for midrange habits.
Of course, there can be no intake leaks and the carb must be assembled properly.
Make sure choke is completely closed.
Do not idle your air cooled engine for 5 minutes at a time!!!
Are you running baffles?
You should end up with 45 slow, stock needle shimmed up .050, and around a 180-190 main with everything healthy.

 

Good advice.
Scott

 

No, I didn't mean holding the throttle steady. I mean blipping from closed to open wide over 5 seconds of time. I did have it idle for that long trying to warm it up so I could make my air/fuel screw and idle speed adjustment.

Float bowl height was too high. Fixed it to spec with calipers.

I had an intake leak on rear cyclinder. Replaced both flanges and new james gaskets. Spray carb cleaner again and hear the RPM drop on both cyclinders when I do. Inspection of the manifold only showed what looks like a knick from a wayward wrench.

still cant solve the cause of the black spark plugs

 

 

 

what year and model?
m

 

97 Wide Glide. Evo and CV carb.

after fixing the intake leak. Put the carb back on with no shim stock needle, 45 pilot and 180 main.
I warm up with 1/2 choke long enough to throw gloves and helmet on and I just took off on the expected 3 min ride to a friends. Pull off my street up a hill and go to shift and I lose acceleration ability. I do a quick U turn and go back towards home and it runs fine. Until I hop off and see a little black smoke out the exhaust for the rear cylinder

Im beginning to think the prob its with the carb itself. Maybe fuel line, tank, vacuum who knows

 

What ignition system are you using? Maybe your issue is not carb related at all, after fixing your intake leaks. Ignition issues are frry often mistakenly overlooked.
m

 

I havent gotten to the ignition yet. I was told by the local HD shop that the symptoms I describe arent related to ignition. I was ready to dump money on a whole new system before I even talked to them. I have found myself inclined to just replace things ***** nilly since its a 20 year old bike that I have no history on except the dealer sold it was an AS-is that passed inspection and had a new tire on the front