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Discussion Starter #1
ok, new to me 1994 fatboy with thunderheader (91 ci), screaming eagle ignition, hi perf cam and S&S carb and certified 13900 mi. sounds like a howitzer every half second at idle. problem is a blip at 65 to 70 mph. the engine seems to misfire on one or the other cylinders, just once or twice and only at those speeds. previous owner thought it may be fuel contamination so it was all replaced, even the fatbob tank for a new OEM. problem still exists. wondering if it is an ignition issue or a mixture issue? thoughts anyone? Thanks.
 

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Discussion Starter #2
hdmd88 said:
If its spitting out the carb its a lean fuel condition. The S&S carb is a two circuit fueling system, the intermediate jet fuels from off idle to 3500 rpms and the main comes on at 3000rpm. You can see by this circuit that both jets are fuelling at the same time in the 3000 to 3500 rpms, this is a porblem with the smaller displacment motors because the plug wants to gas foul in this area, so most people will lean out the main jet or intermenate jet to lean out the overlap fuel area which makes a lean condition in one or the other circuits. The carb can be made to work on small displacment motors with altering the air bleed in the main jet circuit.
If you have stock gearing in your build your tacking 3000 rpm at 70 mph, so you see your right in the problem area.
Timing can also be a factor here but in my experience its the S&S carb.
Thanks for the tip.
 
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