intermittent lag on acceleration

Discussion in '3rd & 4th Generation 1990-1997' started by professore, Mar 31, 2014.

  1. professore

    professore New Member

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    Hi, I'm getting an intermittent lag on acceleration. The tach just stays the same and nothing happens for maybe 1-2 seconds and then she shoots forward. This only happens sometimes. Bike is a 97 with 63k miles, air filter, plugs and oil and filter all done in the last few months.
     
  2. kennybobby

    kennybobby New Member

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    It sounds like poor transition fueling. Has the bike sat over the winter with fuel in the bowls?

    Dirty or clogged pilot jets?
    Dirty or stuck slide in vacuum chamber, or crack/tear in the rubber diaphragm?
     
  3. professore

    professore New Member

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    Bike used every day pretty much. I have had this problem for a while now, had the carbs off recently and diaphragms looked fine, but didn't dig any further. It seems worse when the bike is cold, once it warms up it seems to be OK.
     
  4. Gator

    Gator Insider

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    A complete carb clean will be a good start to figuring it out. Did you change where you fuel up?
     
  5. professore

    professore New Member

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    quick update i drove to and from work today and no problem whatsoever. It's very odd.i suspect something electrical because it's so intermittent.
     
  6. professore

    professore New Member

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    Was fine for days of riding since until yesterday evening after riding about 4 miles. Idle dropped and it was kind of "farting" on accelerating from a standstill. Down on power. Was the same this morning, I had to turn up the idle again to 1200 rpm (it wad idling below 1000). After 3-4 miles I accelerated, there was the lag again, and then it shot forward. After that the idle was up near 2K RPM, so I had to turn it back down. What I don't get is that if it is carbs, why is it so intermittent?

    It's as if something is blocked, and then it unblocks itself.

    By the way I fuel up in the same place all the time, and have been driving on the same tank for a week now.
     
  7. stoshmonster

    stoshmonster New Member

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    Had this exact same issue on my old CB750F. Bike would be running perfectly fine then suddenly lag under throttle,start spitting and popping,and have no power. The odd thing was the problem would always magically cure itself.

    Turned out that the spark plug wire for the #3 cylinder had pulled away from the little nail spike inside the #3 coil and was intermittently making a connection.

    I slid the plug wire back onto the nail spike in the coil and secured the screw-on coil wire connector cap with a bit of electrical tape. Never had a problem with it after that.
     
  8. professore

    professore New Member

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    That sounds more like it !!! Thanks ! I will check later.
     
  9. professore

    professore New Member

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    Went to visit my mum who lives about two hours away on Friday for the weekend. The bike started lagging again intermittently. I had a look on Saturday and I discovered the problem - a loose connector on one of the coils ! Thanks stoshmonster !!!! See the pics below. I hope this helps someone else. A bike that will accelerate strongly from 100 mph (on a closed road) is unlikely to have any carb problems.

    62 thousand miles, kept outside under a cover, used every day in all weathers and still going like a train -even looks nearly new ! I do keep on top of servcing her .... and she has had a stainless steel exhaust system, essential where it rains 4 days out of 5.

    coil_large.jpg

    coil_zoomed.jpg
     
  10. kennybobby

    kennybobby New Member

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    Good Catch!

    Oh yeah that is the sort of good information to share at the outset when troubleshooting...

    That yellow wire doesn't appear to be OEM and appears to be stretched in place from being too short--it does not have proper length to allow flexibility or strain relief such as the black/white one does.

    Good catch on finding the problem.
     
  11. professore

    professore New Member

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    Thanks kennybobby. I guess I thought saying the lag was intermittent was enough. Anyway, it's quite possible that wire isn't OEM - the guy who owned the bike before me was an electronic engineer, and he fitted an alarm (which drains the battery if bike is left sitting a few days) and made some tweaks to the wiring to prevent reg/rec failure. Apart from the alarm annoying me sometimes there haven't been any electrical problems in three years - so I guess he did something right.
     
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