Hey folks.

This place is great, I hope to spend allot more time here.

Here’s the problem.
85’ FXSB 1340 shovelhead. Other specs below…
Recently this bike, I’ve only owned it 1 year, has developed an intermittent stumble under acceleration. Sometimes so badly that it felt as if it was going to stall but usually just a stumble. It comes and goes. Some rides it’s great some not.

The rear pipe started to blue really badly and now also the front pipe. It has been very hard to start when hot. Endless cranking with occasional backfires from pipes and occasional pipe fire. Initially thought the bluing pipes indicated lean, but the plugs have been black all along.

Here’s what I’ve done.
Checked out the ignition system per manual. Seems fine.
Replaced coil just for kicks.
I checked and adjust the float height to 3/16 below bowl gasket surface (it was too high) . I thought that the stumble might be bowl overflow when under G’s, Thought bluing, black smoke and fire could be un-burnt fuel in the exhaust. Am I off the mark here?

I would consider a jetting procedure next but jetting doesn't just stop working. Also, I haven't seen any consistency in the weather condidtions under which it stumbles. Should I do it anyway, and if so could you recommend a procedure that would get me in the ball park. I can jet 2 stokes all day, but I'm new to the Harley thing.

Here’s the bike
85 FXSB Shovel 1340
Never torn into, medium miles
Compression dry 140 front, 130 rear
S&S Super E carb, 072 main, 295 pilot, Idle circuit ¾ out, accelerator pump set at ¾ travel,
Stock ignition, aftermarket coil, aftermarket wires (not sure if solid core or not)
Straight pipes
Autolite 4265 plugs
Aftermarket ignition switch, a little touchy, have to have in just the right spot, but once you put some current though it trying to start it the switch works fine.

Please chime in if you can help. Don’t know what to look at next.

Thanks

Ian

 

very hard to do over the net but it sounds as if you may have encountered a vaccum leak. Check that out as you should have the S&S rubber boot intake?? They tend to crack and do what you are describing. Also the switch is not a good thing as power needs to be constant to the coil not intermitant. Check out the basics first and break it down. To 3 items feul, electrical, mechanical. Are you able to get it to stumble on purpose if so try to use choke during that time. Does it effect it ?? If so the problem would be fuel related, no change ok then we check out the electrical system, first are the grounds, and so one. Then on to mechanical, look for a leaking intake seal, loose or missing parts from carb, mis adjusted cables, and so on you have to break it down so you are not chasing your tail. Let me know how it goes for you. Too bad you are not in phoenix, I have finishing up a 103 shov right now, man does it fly but ohhhh does it shake toooooooooooo[:-]

 

heh, I was about to say the same thing - intake. I have replaced them soooooo many times. Don't over tighten.

 

Backfiring through pipes is usually an ignition, or electrics, problem.

First thing I'd do is replace that faulty ignition switch. If it's that finicky, it's going to leave you stranded somewhere.

 

Have you double checked the intake manifold seals on that S&S? Hearing what you said the bike is doing, I have had past history where the seals had not been installed correct, allowing air to enter the system, inconsistantly. This was very apparent when letting off the throttle, and made the bike a bitch to start when it had warmed up. Out here in Arizona, I make it a habit of changing these seals at least once a year as the extended heat creates havoc in their ability to seal effectively.

HwyAP...

 

Exactly.... backfire through the pipes usually is a rich condition or weak ignition . (causing a rich unburned condition.)
Out the carb lean or intake leak.