1974harley with a super B carb it spits two or three times on a ten mile run, some times when you come to stop. it is a 1974 super glide

Running fuel/air too lean or maybe bad spark plug or wire. Just make sure wires are tight. Might be fouled.

Possibly gearbox sensor faulty.

Check the regulator. It sounds as if it has packed in, when the engine is at idle the alternator output is low, but when revved it will be higher, the regulator controls the top end of the voltage range. Also check the battery connections are tight and free from corrosion.

Sounds lean. Check for intake leaks. Is air filter good and clean. Change the plugs. Has the fuel screen been checked or cleaned lately??


PLEASE post a comment with any more information and also if you get an answer and wish to share it.

You need to clean the carbs. and possible the tank.

The Super B carb is not as forgiving of improper jetting as the Super E model carb due to the lack of an accelerator pump. The only adjustment you have on the carb is the idle mixture screw and idle stop screw. The idle stop screw simply adjusts the idle speed of the engine. The idle mixture screw should be adjusted somewhere between 3/4 and 1 1/4 turn out from the bottom. If it is out of this range, the carb is not jetted correctly.

Through experience over the years I've found that the Super B used on a Big Twin Harley should be jetted 29.5 on the slow jet with a 70 or 72 on the main jet. If used on an Ironhead Sportster, slow jet of 26 with either a 66 or 68 main jet.

The way to tune the carb slow speed circuit is to allow the engine to warm up and adjust the idle mixture screw one turn off the bottom. Then try to rev the engine. If the engine does not rev cleanly, try coming out a half turn on the idle mixture. If it seems to help, continue until it revs cleanly. If this is the case, you slow jetting is too lean, install a richer jet and repeat the above procedure. Once you get it tuned to where the engine revs cleanly with the idle mixture screw at one turn out, you low speed jetting is correct.

The high speed jetting is not quite as simple to set as this has to be done on the road. I usually find a long uphill run to test the jetting to keep top speeds reasonable. At about 55-60 miles per hour, roll the throttle on in high gear. Feel the way the engine pulls. If it pulls good, back off on the throttle about 1/8th turn. If it pulls better, it's just slightly lean. If when you roll the throttle on, the engine starts spitting back through the carb and doesn't run well, you are way lean. Either way move upwards on your jet size one step at the time and retest.

If the bike seems sluggish and blows black smoke when you do the "roll-on", you're too rich. Install leaner jet one step at a time.

Now, most people confuse a "mid range stumble" with a carb problem. All efforts to tune this stumble out done on the carb are futile. The problem is in the exhaust system. Most bikes do not like open drag pipes for street use. They will exhibit this mid range stumble. The remedy is to put a bolt with three nuts on it on the inside of the pipe or any other means to create just a bit of backpressure on the exhaust. This usually cures the problem or at least makes it easier to live with.

Full tuning procedures can be downloaded on the S & S site. Go to "Technical" page, then "Installation instructions" to download the full paperwork that came with your Super B.

I hope this helps and Good Luck.

Plus should be set about 0.25 to 0.30 not.025 For the points 0.18 Might have to replace a main jetting in carb it could be clogged. If it continues that maybe readjust Valves.

do u have the correct spark plug the one recommended by the manufacturer

check your fuel filter that is common, they get clogged.