Tried to start with Killswitch on - then boom - now seems to have a misfire

Discussion in '3rd & 4th Generation 1990-1997' started by thurst, Jan 31, 2017.

  1. thurst

    thurst New Member

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    Hi all. Well I had a weak moment and just picked up a 1990 Gen 3 in pretty good shape for a fair price. She has about 70K miles on her but is good overall and I know this series can run for quite a while longer if taken care of. I have a soft spot for this bike and felt I wanted another project and would like to bring her back to her former glory sort of speak. I rode her home and she ran great. Now onto the issue

    The next morning I was a dope and tried to start her with the kill switch on. My 09 VFR800 was fuel injected and wouldn't start if I tried this so I was not used to checking the kill switch position before starting the bike. I know what happened, fuel in the exhaust and as soon as I noticed the kill switch, of course I turned it off and started again, really really big boom!

    Now, she starts OK, but at first was throwing a lot of what looked like dissipating steam (unburned fuel?) but after a few minutes starts to run rough like she has a big miss and the rev's won't go any higher than 3-4k before she starts to pop more. Eventually she will quit.

    I was planning on stripping her down doing all the normal stuff, carbs, plugs, filter, valve clearances etc etc. But I am wondering now have I bent a valve or something? Maybe developed an exhaust leak and she is running super lean? Would a kill switch pop from startup cause an issue so large where it won't run any longer? I probably cranked it a good 10-12 times before I realized the switch was on.

    Just looking for suggestions on where I should start.

    Thanks guys!

    Trevor
     
  2. rjgti

    rjgti New Member

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    most likey your float height on two cards are now set incorrectly due to back fire of that magnatude
     
  3. thurst

    thurst New Member

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    Thanks for the reply. So just thinking through your suggestion a bit and I would like to understand the mechanics of it. Since an exhaust pop like this results from unburned fuel in the exhaust system it gets ignited from hot gasses being released on an exhaust cycle of a particular cylinder.This of course means that one (maybe 2) cylinders have their intake valve open at this moment causing a shock wave in through the carbs on those cylinders. This would push the adjustment tab on the floats out of height. Improperly set floats causes more fuel to dump into the cylinders causing the condition? It runs ok when cold and starts up good (with choke) but then when I let the choke down after a few minutes she starts to miss a lot. is that about correct?

    I was going to plan on removing and servicing the carb but was going to stay away from the floats (based on others suggestions) but now I think I will try to adjust them. Would you happen to know the proper float height for my carb? I'll check around in the manual I have and will need to look for the procedure. Any suggestions there would be great.

    I appreciate the response and any replies.
    Thanks

    T
     
  4. rjgti

    rjgti New Member

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    I will try to look it up later
     
  5. rjgti

    rjgti New Member

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    .35 is what the manual calls for
     
  6. kennybobby

    kennybobby New Member

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    This sounds like a classic case of clogged pilot jets which have the smallest orifice and are easily fouled with debris and ethanol jelly.
     
  7. GreyVF750F

    GreyVF750F Member

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    fouled plugs.
     
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