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losing top end power

softail 88

softail 88

Member
i am a person that runs my bike hard.i have older fxstc with good hp. it has been back firing on top end if i dont get on it runs great once i try to race i lose power on top end just had the carb readjusted and cleaned and the bike tuned better ran great for a couple days then the problem started again could it be my coil hitting and missing like that i know for sure its not a fuel delivery prob just went over all that any help or thoughts would be great thanks
 
Why/what performance plugs and what wires, no beating the stock parts on these bikes.

Did this start after replacing these parts?
 
this started before the plugs and wires both are SE from harley i have high performance ignition so i use H.P. plugs and wires
 
What ignition, is the engine stock?

Have you eliminated fuel problems or did this start soon after a fill up?
 
softail 88 said:
it has been back firing on top end
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Back firing on top end, like it was said, Electrics.

I know it is a crude way to test something but can you pull a thick orange spark with a "spark gap" with engine running. (test both sides)
 
100% sure its not a fuel prob went over all that first.the engine is not all stock.the bottom end is the heads bored a little over.mid size cam.i have a twin fire 2 dc6-5 igintion.HOPPIE what do you mean pull the plug and see what color the arc is and what would that tell me
 
softail 88 said:
HOPPIE what do you mean pull the plug and see what color the arc is and what would that tell me
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The color of the arc gives you an idea of how much "spark duration" or millijoules of spark energy you have.
Faint blue sparks are weak. Thick orange sparks are Healthy. This is simple but effective way to see if your ignition has a healthy "reserve" spark. Remove both plugs so the engine will spin easily while cranking. Take an old spark plug you have laying around. Set the gap to .060" or some very wide gap. Install it into one of the plug wires. Place the shell of the plug against the engine and crank the starter. Look at the spark. It should be easy for the coil to jump that wide gap and with a .050" gap it should be a nice thick orange color.

It is only a basic test but it may give you an idea of what is going on.
Of course you have 2 sides to test. When you test one side, it is a good idea to have the other spark plug wire (the one not under test) shorted to frame ground.
Now just mirror image what your doing to test the other side.
 
I just noticed the year of your bike. Does this engine have points or were they solid state in that year?
 
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