One cylinder not firing right at below 3000 RPM

Discussion in 'Mechanics Garage' started by Jonj75, Jun 24, 2019.

  1. Jonj75

    Jonj75 New Member

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    Hey all, I just joined the forum but i've been a silent reader since I've been eyeing a VFR of my own for a few months now and I finally jumped on one.

    I just picked up a VFR after saving up and finding a great deal on a near mint one with 25k Miles and a lot of paperwork from the dealership for every service interval up til he sold it to me. The bike has been obviously maintained BUT he told me it sat for almost 5-7 months basically unused except for the odd startup.

    I noticed on the ride home that it came off idle very poorly and my brother stalled it a few times on his go around. We both noticed that around 3-4k rpms the power surges really strong and it runs great. So the last couple days I've been pulling things apart for inspection and I took a temp gun to each header and noticed the left front header (from seat of the bike) is 150 degrees cooler than the other 3! I had my brother hold the throttle at 4000 and the heat shot up to match the others within a minute or so but as soon as it went down to idle the temp would start to drop dramatically again.

    I haven't had a chance to check the plugs, but I'm starting to think it may be a partially clogged injector or a starter valve sync but wanted to ask for some other opinions. I don't have a vacuum gauge so I can't check the sync. I'm running a couple of tank with some seafoam in it to hopefully clean some of the gunk out as well. Any help would be apprieciated!
     
  2. Jonj75

    Jonj75 New Member

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    One last thing, I was also thinking it could be the Fuel Pressure Regulator as I've heard they can cause fuel to leak through a vacuum line of some sort into the carb and have it run rich. anyone know how I would test that?
     
  3. Thumbs

    Thumbs Member

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    The year would be very useful
     
  4. Darth Vader

    Darth Vader New Member

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    750s have carbs, 800s injectors. Id start by fitting new plugs ( easy and cheap ) then a starter valve sync. Can you borrow some gauges or post your location to see if someones close by to help ?
     
  5. Allyance

    Allyance Insider

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    If yours is an 6th gen 800 (2002-2013), then it is fuel injected. I had an 2003, and it ran rough below 3000 rpm, which I found out was normal for this generation. An aftermarket fuel controller solved the problem. You may also have a gummed up injector, which the Seafoam may solve the single cylinder problem.
     
  6. Terry Smith

    Terry Smith Member

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    Without knowing exactly which year VFR you have, I'm assuming it is an 800 with FI as you mention the fuel pressure regulator. On the 98-01 bikes the vacuum hose for this is the front right cylinder, and the 02-13 looks to be the same.

    I'd be doing the simple stuff first, and replace the spark plugs. I doubt that a starter synch will assist this as all the butterflies move together in any case so you will have airflow to the offending cylinder through that. The synch really helps the idle and off-idle smoothness.
     
  7. Jonj75

    Jonj75 New Member

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    Sorry I forgot about the year it's a 2002, Woke up and now the battery is dead (drained from 12.5 to 7v overnight). Now i'm thinking it could be electrical or perhaps a 2 part issue. Testing the regulator and other connections and swapping the battery as unsure of how this one was kept/maintain or it's age.

    Edit:
    I swapped in a tested good battery (from my brother CBR1000rr), it started fine but still one cylinder wasn't running right (front left from rider seat). I checked the battery voltage at idle and it read 13.6 and at 5000 RPM it reads around 13.75~13.8. It would seem something isn't right there either. I will be ordering some spark plugs soon as I don't feel the problems are related and the bike could use a new set anyways. Gunna try and find a guide to start checking the charging system and such as ive never done that.
     
    Last edited: Jun 25, 2019
  8. squirrelman

    squirrelman Member

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    in the 13 volt range your charging system is doing fine. i'm guessing bad injector.
     
  9. Jonj75

    Jonj75 New Member

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    Well slowly the injector seems to be clearing up. After starting the bike a few times with sea foam in the gas tank it it gets smoother and smoother now it sorts itself out at about 2000 rpms instead of 3500. I ordered a fuel rail with 4 injectors in it for around 20 bucks (ebay win) so I can keep riding and have less downtime. I did notice the stator wires are pretty hot once the bike has been on a while, too hot to touch for longer than 30 seconds. I read online that could be a bad ground or connector? I'm installing the VFRness today so we'll see if that helps. If not more digging required unless that's how it's supposed to be?
     
  10. Diving Pete

    Diving Pete Member

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    Dead battery, stator wires really hot - I'd start at looking at doing THE DRILL first.
     
  11. Jonj75

    Jonj75 New Member

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    I did that, and detected nothing that indicated something was wrong. Did it twice to make sure nothing appeared while the bike was hot too. I'm digging through wires and parts trying to find something wrong but so far no luck. I will however admit my knowledge of multi-meters and electronics testing is very limited. I'll probably do it a 3rd time and see if anything changed after doing the VFRness or if I can catch anything I missed before.
     
  12. Jonj75

    Jonj75 New Member

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    I found the issue! It was a defective spark plug. Looked totally fine and works at higher RPMs but doesn't spark well down low. Previous owner used IMR9C plug as a replacement instead of IMR9B's. I can see why too, they're almost twice the cost. Swapped the coils over and problem didnt move, swapped the plugs over and the problem followed, guess I didn't wait for the bike to get hot enough last time! I also put in a new injector but it seems that wasn't the issue, guess I have a spare.
     
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  13. Diving Pete

    Diving Pete Member

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    Thats great news..
    'Mental Note to self - Ask Owner if all plugs are the same ! '

    Glad to hear that's the cause.
     
  14. scottbott

    scottbott Member

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    years and years ago I had an 1972 Audi 100 LS and a plug went down so I replaced it with a plug that was in my garage (wrong type) and ran the car but forgot to replace it and went to Friars in Aylesbury to see Motorhead when they were doing the 'Bomber' tour, one of my mates had a Triumph Stag and I raced him home until I heard a 'tinkling' sound, got home and I had done a piston which just happened to be the wrong piston one. I went to the Audi dealer to get a piston and they gave me a price of £98 I said I don't want the set just one and they replied that was the price of one!, got the engine rebuilt but that was a very expensive lesson learnt, what a cockhead
     
  15. Jonj75

    Jonj75 New Member

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    Just to follow up, I replaced the plug and all the misfires went away. It has some other issues but this one is solved.
     
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