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hi all i am new member need help

paul5

Member
not sure where to post this so here it goes . i have a 98 fxds been running fine with ultima single fire setup coil and module standard carberator im pretty savy backyard mechanic ive always fixed my own vehicle for many yrs but this has me stumped about couple weeks ago bike little hard to start then when it did only seem to hit one cylinder so i reved up and at above 2k rpm the other kicked in lowered and it went out again so reved again it kicked in and after few seconds it seemed to stay working but every time i would start had to do this a week went by and then it got worse would only work above 1500 rpm so i pulled plugs looked fine put them in the wires and held against head bolts and cranked bike both had spark so put in and started bike sparayed carb cleaner by intake to head seal area both of them and the carb side also no aparent leak took carb out and changed them anyway had a set of seals cleaned carb and still no difference so i caint understand why its doing what it doing if it were fuel it would be both cylinders so i am thinking it has to be in the sparke but i have spark and compression wouldnot go in and out it would just fail im thinking coil but i dont trust test cause in past ive had test perform good and when i finaly came back to conclusion the problem had to be coil i would remove and find the backside had cracked and ozed out inside stuff so the test i caint trust if anyone has knowledge of this symptom and cause please respond . i just caint figure out how have spart at plugs both but when try to start the front cylinder wont fire and also i put a test ligh to the rear spark plug when engine runningg only one cylinder and it killed but when i put on front it made it fire but then bike kills so weird
 
You post tells me you are in fact competent, so I'm just gonna throw some guesses at you. You say you have compression, but have you put a compression gauge on both cylinders? Did this malfunction start the day after a hard run, or a missed shift (hinting at bent push rod or valve). Are the Ultima coils separate or two/one? Try switching them. Does your Ultima ign. have single and dual fire capability? If yes, try the dual fire setting. That's all I can think of right now.
 
Welcome to HDT from sunny AZ.
You may want to try this too. You may show spark when you tested it but it may be to weak of spark to fire.


If you want to "bench" test a coil, remove wires, attach a hot 12 volt to the battery (batt, +, etc.) terminal. Then attach a wire to the ignition (ign) terminal and touch ground and remove. Should throw a spark from the high tension lead with each application of 12v and removal. The ground wire basically imitates the function of the ignition points/module. If the high tension lead terminal is gapped a reasonable amount from the engine, there should be a bright white spark. Weak or orange spark indicates (low voltage...or) bad coil output.
 
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Welcome to the forum from Scotland
If compression is good and spark is good must be fuel if there is no leak at the intakes to the cylinders not enough fuel may have it run on 1 cylinder till the engine has warmed up as the fuel/air mix can be weaker on a warm engine
another look at the carb ensure float height is correct etc

Brian
 
tks will check coil and as far as carb its vacum slide it is working and it has been fine for yrs caint see it getting lean i had rear cylinder plug foul about yr ago went one plug hotter it stilll has slight soot black and front is kinda tanish which indicates it was recieving good fuel oh i did change plugs about month ago thats how i know colors i checked after a week and still look same now i even did the vacume test on voes it checked out ok just never had a coil fail like this but then never had a single fire coil before either its on unit with two plug in for plug wires and three post for fire i gues it all part of the ultima 2 single fire kit been on bike for yrs and yrs was hope someone had their coil fail like this i mean i looked at spark both plugs looked same but ill test coil in morning tks i dont think it mechanical cause never heard any mechenical failure sound usualy you can tell if bent pushrod it woul always not fire if compression was bad it would not get better as engine warms up but will check compression also tks

also anyone ever have isue with the caint rember what its called but it sense crank position and tell ignition to fire could that be acting up i thought they just quite working
 
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also anyone ever have isue with the caint rember what its called but it sense crank position and tell ignition to fire could that be acting up i thought they just quite working

Crank position sensor, they can get dirty and sometimes need to be removed and cleaned or replaced.
 
Sounds like some good advice from everyone, You're in good hands. When doing a compression test, look the throttle open and hold the slide up with one finger while cranking.
 
well compression test was good 120 even both cylinders which i alrdy knew i listen to bike while riding not just blind.hehe. so i messed around again and i pulled choke and started bike and didnt let off choke bike ran and didnt miss both cylinders but soon as i let off choke couldnt keep bike running so i am prety sure now it has to be carb or maybe tank vent not letting air come in so a friend has a s&s carb he giving me he wants his stock carb back on so he giving me his s& s soon i will know
 
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