87 VFR 700 f2.....dead spot mid range....need help!

Discussion in '1st & 2nd Generation 1983-1989' started by trfdp3, Apr 3, 2012.

  1. trfdp3

    trfdp3 New Member

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    87 VFR 700 f2 dead spot mid range....need help!

    Hey folks I just got this 87 VFR 700 F2 and I've brought the carbs back to stock jets and set the floats at both 7mm and 9mm. Everytime I take it out for a spin it has this massive dead spot in the 3k-6k rpm range, ESPECIALLY, uphill or higher gears. Once it get past the dead spot it flies like a bat outta hell. I've tried almost everything i can think of. Got new carb boots to solve vacuum leak, it has the cali emissions junk. It idles great but cruising is just treacherous. I've tried tuning with the pilot screws and still no help with the dead spot. It runs very rich and its just a nightmare trying to lean it out. Did compression test on each cylinder and passed. I love the bike its just this issue is killing me.:mad: Any suggestions?
     
    Last edited: Apr 3, 2012
  2. Dukiedook

    Dukiedook New Member

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    Recheck the float valves and maybe set them lower. Air filter OK? Carb jest and passages thouroughly cleaned? Spark plugs recently changed? HT wires OK?
     
  3. Captain 80s

    Captain 80s Member

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    Stock exhaust? Air box snorkels still in place? In my experience that bike really doesn't like the snorkels removed (usually)... huge mid range flat spot.
     
  4. orion3814

    orion3814 New Member

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    yeah unless the carbs have been jetted properly to accommodate for changes make sure everything is stock or you will have flat spots, for instance my baby ceptor i tossed a set of super traps on it and when i would pull the disks off for a bit to make it louder it would have a flat spot then when i put the disks back on the flat spot went away.. i was changing the exhaust tuning when i done that caused a very lean flat spot about 5k rpm.. not good because thats where it cruised and if i ran it lean like that would eventually end up detonating the engine into a pile of melted aluminum..
     
  5. trfdp3

    trfdp3 New Member

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    Yea it's got a 4-1 yoshimura and snorkel is removed. Floats are currently set at 9mm. Air box is intact no holes drilled or anything. I do still have the snorkel.
     
  6. Dukiedook

    Dukiedook New Member

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    Something clogged with the CA emissions stuff? Something might of made a nest in there and would limit the air coming in.
     
  7. TOE CUTTER

    TOE CUTTER Mullet Man

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    Are the needles stock? Dynojet needles are the devil and I insist on them being removed when I rebuild carbs for this very reason.
     
  8. trfdp3

    trfdp3 New Member

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    The emissions stuff may indeed have a clog but I haven't really gotten into the emissions crap. And toe the needles are stock to the best of my knowledge but were shimmed with 1 extra washer in each needle. I removed the shim and put it to 1 washer per needle hoping to maybe lean out the richness.
     
  9. squirrelman

    squirrelman Member

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    Problem is likely within Cali emissions stuff, an open line that should be closed or a closed line that should be open.
     
  10. jcarpfishman

    jcarpfishman New Member

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    trfdp3: I will join in as I am having virtually the same issue right now (minus the Cali emissions stuff). '86 VFR700 that was running fantastic before with all stock carb pieces (as best as I can tell)... just installed a Yosh 4-into-1 pipe on it and I now have the same dead spot in the mid-range. Low end sounds and runs extremely well, but as soon as I get beyond 3K, it bogs / gets lumpy and in general runs poorly. I've only managed to get it up to redline once since the exhaust was installed, and it ran ok there, but not fantastic. Before, the application of the power was smooth, consistent, and seemed to continue pulling all the way to redline. Now with the lumpy mid-range, it seems to have difficulty gaining momentum in the upper range once you get there.

    I'm guessing your issue is not with the emissions stuff as I am having the exact same troubles without it. From all of your posts, it seems to me that we're at about the same point in the diagnosis. Spark plugs only have 2,000 miles on them, have been pulled, checked, and re-torqued. Carbs were just cleaned very thoroughly and synced, carb boots are in good shape and not leaking, floats set to 9 mm, stock air filter with stock airbox (snorkel in place).

    The only thing that I am unsure of, and I'm hoping Toe can chime in... my needles are tapered, although they do not have the notches for changing clip position like the DynoJet ones. What exactly does a stock needle look like? I seem to remember a number stamped on the top of mine... 6BP or something like that... does that sound right?

    Hopefully, we will come up with a solution faster with two people troubleshooting!
     
  11. squirrelman

    squirrelman Member

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    I think it's typical for many 4-into-one setups to have a flat spot somewhere, and it's usually something that can be minimized or eliminated by fine tuning on dynamometer or road.
     
  12. trfdp3

    trfdp3 New Member

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    See now when i get to the dead spot and hit the choke which is an enrichener essentially it bogs even more which leads me to believe its too rich cuz of it was too lean it wud have accepted the fuel and stopped bogging.... That's my logic at least I Cud be wrong
     
  13. squirrelman

    squirrelman Member

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    Get a mate to follow you; sometimes the big bog is accompanied with black exhaust smoke....too rich, so you might want to remove washers.
     
  14. Chris71Mach1

    Chris71Mach1 Insider

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    aaaaaaaaaand THERES your explanation! i hate to be the bearer of bad news, but 4-2-1 exhausts are pretty much known for causing this flat spot in the torque curve of these old bikes. the same thing happened to my bike when i installed my 4-2-1 years ago. many have experienced this, some have tried at length to get around it, but the bottom line is that you now have a flat spot in the torque curve (mine is from 6k-7k) thats pretty much there for good.

    as for the airbox, i have my snorkel removed as well, in addition to a K&N air filter and the recommended lid drilling that the Dynojet stage 2 instructions recommend, and lemme tell ya, between the exhaust and the intake, that thing sounds amazing at WOT.

    sorry about that flat spot, but youll learn to enjoy everything else about the old girl, i assure you.
     
  15. trfdp3

    trfdp3 New Member

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    ok folks so i stripped the cali emissions stuff per some of TOE's past posts haha and it runs great. Still a small flat spot not as bad as before. I stripped the carbs AGAIN and cleaned em thoroughly. Just becomes an issue when under a load in higher gear but easier to manage now. Maybe some more fine tuning wud fix er up?? Thanks everyone btw for chiming in and helpin lol
     
  16. rc24rc51

    rc24rc51 New Member

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    You're running a full stage 2 jet kit? You have a full exhaust or slip on? Mine is all stage 2 with slip -on but pulled the stage 2 needles and went back to stage 1's..........flat spot gone. 90 rwhp.
     
  17. jcarpfishman

    jcarpfishman New Member

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    BINGO... this is the kind of information that I've been looking for! I refuse to accept the dip in the mid-range... so it would seem with Stage 2 jets and airbox modifications, but Stage 1 needles, you are able to eliminate the flat spot in the mid-range associated with a 4-into-1 exhaust setup??

    I'm using the stock headers, and a 4-into-1 Yoshimura tail end. Currently have all stock components in the carbs, but I've been wanting to know what to do to keep the exhaust AND maintain the mid-range that I had before the swap. There is not an excessive amount of information about the adjustments required to keep her running well with an aftermarket exhaust setup. Hopefully, we can file away some information so the next person that comes along doesn't have to do too much digging.

    What brand jet kit did you go with? I was going to call Factory Pro this week and see if they have anything filed away in their database...
     
  18. rc24rc51

    rc24rc51 New Member

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    I have a Dyno-jet stage 2 set up in mine. Yosh 4-2-1 slip on, modded air box w/snorkle intact. mains are 128's, stage 1 needles but i can't recall where the clip is set. The stage 2 needles add too much fuel even at their lowest setting. Perhaps with a full exhaust or cams they'd work but not with a slip on. I found this out with the help of a Eddy Current dyno. I could go to a slightly larger main as the O2 readings were boarderline @ WFO. Very happy with how it runs now.......pulls like a bitch (47ft lbs) even with 45K miles on it!
     
  19. Chris71Mach1

    Chris71Mach1 Insider

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    this thread is really making me re-think my carb setup. ever since i had the stage 2 jet kit installed in the old viffer, ive been getting an avg of 26-27 mph out of it, and you can CLEARLY smell how rich it's been running. i never thought that the needles could make such a huge difference. I dont know what most would consider a slip-on (be it just the muffler, or if a 4-2-1 baffle would be considered a slip-on system, as I cant for the life of me find any aftermarket header pipes for this bike). I guess if anybody has a set of stage 1 needles they want to part with, let me know, cause id really like to see how my bike would react to them....

    (and for those with a stage 2 jet kit with stage 1 needles, where do you have the needles set at??)
     
  20. rc24rc51

    rc24rc51 New Member

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    I think my needles are set w/ clips in middle position or recommended base setting. You can buy the stage 1 needles from dyno jet........... part # DNO 108. As for your exhaust if you're running the stock OEM down pipes or (headers) anything after that would be considered a slip on. I get 42-45 mpg W/ yosh 4-2-1 slip on, k/n filter, drilled air box w/ snorkle. Find a LOAD control dyno and spend a couple of dollars. All you'll need is a couple of pulls w/an O2 sensor in your exhaust. My guy did 5 pulls for $50.
     
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