backfire issue? maybe?

Discussion in '1st & 2nd Generation 1983-1989' started by pokerplayer6989, Nov 11, 2009.

  1. pokerplayer6989

    pokerplayer6989 New Member

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    can you guys help me. i was having a bit of a popping issue that i could here out the exhaust. well i synced number 3 and number 4 to number two. and now ive notice the popping is louder and only coming out of the left exhaust? :confused:any ideas. note i havent been able to do number 1 it got dark out. it also seems to get worse as the bike warms up. also very noticable when im coming up to a stop and engine breaking. its driving me nuts:crazy:. help any one?
     
    Last edited: Nov 12, 2009
  2. tinkerinWstuff

    tinkerinWstuff Administrator Staff Member

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    Has the bike ever ran correctly for you?

    Without hearing it for myself, it sounds like one cylinder isn't firing or is flooding out (too rich) and the fuel is lighting off in the exhaust.

    The fact that it appears to get worse might be due to the fact that the collection pipe gets hotter and lights the fuel off more often.

    Again, it's just a first theory but I go back to my question, "has the bike ever ran correctly for you?" When did the problem start, did it come on gradually or happen all of a sudden, and have you done anything to the bike recently?

    One of the first and easiest places you could start is just to do a header temp check. Start the bike up from a dead cold temp. Put a finger (gingerly) on each header pipe and see if they get hot right away and if you have a cold pipe. You might find a cold pipe on that left side you are hearing the popping from.

    Be carefull, the pipes will burn your finger after only one or two minutes of running.

    If I found a cold cylinder, I'd wait and see if it comes online after a couple minutes of running. Sometimes one cylinder might have a choke circuit that doesn't work as well as the others and after the bike starts to warm up, the cold cylinder will start firing.

    If this theoretical cold header pipe I speak of never gets hot, I'd check for spark next, and then for a stuck float.
     
  3. cebuVFR

    cebuVFR Member

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    my 3rd gen backfires too.
     
  4. fredsncoma

    fredsncoma New Member

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    try plugs

    When this happened on my Gen 2 it turned out to be the plugs. mine the gaps were closed. it is an easy enough check. M<in turn out I was using PR which atre prtector tip plugs and at high RPMs the pistons were coming up high enough to close the gaps on the plugs. swithched to none PR plugs and never had a problem again.
     
  5. tinkerinWstuff

    tinkerinWstuff Administrator Staff Member

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    I guess what I said only applies if you've seen a significant drop in HP associated with your popping. I went back and re-read your post and didn't see any mention of HP loss...
     
  6. pokerplayer6989

    pokerplayer6989 New Member

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    well i cant really say yes or no to that as i bought the bike from a guy in flordia. for 700 bucks. it was way better looking in the pics than when i had it shipped to my house. at that point in time i couldnt just get rid of it so i started fixing it. so to tell you i dont know if it ever really ran (right) because a this is my first bike and b ive never rode a street bike let alone a 86 vfr so i dont know if there is any hp loss.i know since ive had it ive had charging issues but thats most the rr. but hte bike has no problem hit 135 and any were in between no hesitation that ive noticed. so see if you can diagnose from that. also it should be mentioned im running dual yoshmira exhaust.
     
  7. pokerplayer6989

    pokerplayer6989 New Member

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    whar are PR i have nkg plugs r type i believe
     
  8. tinkerinWstuff

    tinkerinWstuff Administrator Staff Member

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    If you are hitting full speed then disregard my ramblings earlier in the thread. You won't hit 135mph with a cylinder that's not firing.

    However, that doesn't mean that you couldn't still have a cylinder that's running rich. How is your mileage? Have you put in a new set of plugs recently and looked at their color after riding a bit to see if its burning consistent across all four?

    It might just be a touch on the rich side and not much to worry about. My 660 Yamaha Grizzly behaves similarly when I ride at altitude. I'm jetted for 4500ft and when I run up over 8000ft I can get a similar behavior because the machine is running rich and unburned fuel is lighting off in the hot pipe - especially during engine braking!

    Running a little rich will sacrifice fuel mileage but will also allow the engine to run cooler.

    I would start by looking at your plugs. If the plugs look consistent and your wires are all in good shape, engine compression all within 10%, you could consider stepping down 1 step in jet size and see how it runs.

    just my opinion...
     
  9. xtravbx

    xtravbx New Member

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    Could be improper fuel mixture settings - just basic carb issues.

    Does it back fire while accelerating? Or when the throttle is closed and your engine braking?
     
  10. fredsncoma

    fredsncoma New Member

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    It has been a looong time, but I am positve they were NGK7PR which makes them a rsistor type plug and they are just a butt hair longer than other plugs. It may just have been R, see if you can get the same plug without the R and compare them. Either way, pull your plugs and check gaps if they are smashed close it could be your problem.
     
  11. steven113

    steven113 New Member

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    Try pinching off your hoses connected to your pair valves with some sort of clamps and then take it for a spin. If one or both of the pair valves are stuck open it could cause similar symptoms.
     
  12. tinkerinWstuff

    tinkerinWstuff Administrator Staff Member

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    :confused: "pair valves"? I can't think of what that is a reference to...
     
  13. GreyVF750F

    GreyVF750F Member

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    If this is a popping/crackling in the mufflers when decelerating/engine braking your pilot circuit may be on the lean side. A lean mixture is easier to light off compared to a rich. When backing down-slowing up, throttle basically off, a lean mixture will enter the hot pipes and go bang. Try turning the pilot screws out another 1/2 turn at a time and see if that doesn't change it. Also it may intensify the noise if your mufflers are burnt out-inside packing is gone. The packing will muffle some of what your hearing also if your running lean.

    My bike does the same. I normally tune my motors towards the lean side for low and mid range power. This is one of the side effects.
     
  14. steven113

    steven113 New Member

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    The older gen vfrs may not have them? At least the 5th and sixth do, it is part of the emmisions system. 1 vaccume line that comes off of each valve cover. It is a somwhat popular modification on the later model bikes to completely remove the pair valves and block them off with plates to reduce weight and unclutter your engine bay as they do nothing for the performance of the bike and are basicly just another system to maintain. I am not familiar with the mid 80s bikes so I do not know if they also have this system but typicaly on the later model bikes symptoms of the valves being stuck open would be poping under decelleration. There are quite a few posts here if you searc pair valves. Hope this helps:biggrin:
     
  15. tinkerinWstuff

    tinkerinWstuff Administrator Staff Member

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    Poker - Before making willy-nilly carb adjustments, just take 10 minutes and pull your plugs. Ensure that all four plugs have similar color and deposits. You can google "spark plug reading" online to get color photos of different burning conditions. This will also give some clue as to whether the motor is running lean or rich.

    The idea is to be methodical and not creat more problems. Check the plugs and report back. If all 4 are consistent, then we can go to the next step which may be carb adjustments. Take a photo of your plugs if can and post it. Make sure the white balance on your camera is set properly or the color may not look right when viewed online.

    While checking your plugs, you can look to see if a previous owner has removed the tamper resistent caps covering the pilot jets. If the caps are removed, someone may have tampered with the jets (duh). If the bike is stock, the jet covers are in place, nothing out of the ordinary with the plugs, and you are running below about 4000ft above sea level, then the carbs likely need a cleaning.

    Step one - check the burn on your plugs and what Fredsncoma said about plug gap/type.

    Here is a photo of the pilot jet location. Just like automobiles of the same era, the factory put a pressed in cap covering the screw.
    [​IMG]
     
    Last edited: Nov 13, 2009
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