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1998 1500 vulcan classic fouling plugs on rear cylinder only

5K views 6 replies 4 participants last post by  sfair 
#1 ·
Hi, folks
Ive got a 1998 1500 classic with 2 inch v/h staggered pipes k&n air filter stage 1 dyno-jet kit that keeps fouling rear plugs
suspected ign wires at first so they were changed problem still came back sometimes 1 tank of gas sometimes 10 tanks of gas
suspected hydraulic lifters were failing due to old thin oil still no difference
have the hottest plugs in the bike now
leak-down tests great as well as compression
went over all electrical connections and still nothing
has a single carb feeding both cylinders so i cant blame jetting cause front cylinder plugs are burning perfectly
once i replace fouled plugs it runs like a dream again but unpredictable for how long
checked fuel tank vent was plugged once corrected it still fouled plugs and i mean fouled to the point where it would stop firing and cough and sputter
ive been scratching my head with this normally im pretty good at searching for these kinds of problems but this one has me baffled :confused:
 
#5 ·
heavy black soot like its loosing spark
existing problem
the problem is that it happens so fast and speratically i dont have a window to identify it
once new plugs are inplace it runs like a champ again
when bike was purchased it was missing the jet kit was never installed so ot was gutless
i installed the jet kit with hopes that this would also solve the fouling issue as it only made sense
ive installed tons of jet kits before on several different makes and models but this one has me against the wall
 
#6 ·
I resescenly had a similar problem. Rear cyl was fine, front not firing. Was fouling front plugs. Turned out the power wire to the coil was loose and barely hanging on. The weather cover was completely on but the spade conn inside was loose and would lose contact with the vibration and that was causing the front cyl to cut out.
 
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