1991 Gen3 Running problem

Discussion in 'Mechanics Garage' started by YorkshireVFR, Sep 11, 2021.

  1. YorkshireVFR

    YorkshireVFR New Member

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    Really need some advice on this, my bikes a Gen 3 1991 FM. The bike starts first time and idles well while on the full stand but can make the occasional small backfire. When I take it on to the road it hesitates when I accelerate out of 2nd and 3rd gear, then the power comes on. While on the stand I can take the revs upto 11k without a problem but it struggles to get above 5k on the road. When braking and dropping down the gears it has a tendency to cut out particularly while in neutral and when stopping at a junction also cuts out. There's a horrid kinda clunking noise around the rear left hand side cylinder area when it's about to cut out. I thought it maybe a faulty coil so I sourced a replacement coil for number 1 cylinder, but the problem still present. Any advice greatly appreciated
     
  2. squirrelman

    squirrelman Member

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    was the bike in storage and not used for months or years? in any case, it's most likely in need of carb cleaning work, fuel filter replacement, and a proper petrol tank flush and cleaning.
     
    Last edited: Sep 11, 2021
  3. jethro

    jethro New Member

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    Since it is running you could try a strong dose of Chevron Techron fuel system cleaner. It has done some amazing work for me over the years. Another thing to do is keep the ethanol gas out of it if you can find fuel without it.
     
  4. ridervfr

    ridervfr Member

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    If bike was in storage and not used for any serious length of time, your going to have to pull the tank off and do a full carburetor service. Read: each carburetor needs two OEM Honda rebuild kits. It adds up in money but the smiles you get from a properly running Gen3 bike are priceless. Condition of the inside of your gas tank is critical as it will ruin a fresh over haul. Consider getting new insulator bands for the carburetors as well as doing a thermostat replacement along with o-ring, while your in there. Could also consider replacing fuel rail o-rings which could be a difficult job depending on your mechanical expertise. If you do all this stuff, you will have a larger hole in your wallet but will have a 100% dead reliable bike that you could ride anywhere. Don't ask me how I know this :mech:
     
  5. squirrelman

    squirrelman Member

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    something i learned very recently, honda changed the length of the "air funnels" (velocity stacks) somewhere in the 1991-1993 production run.

    sept 5, 2021 017.JPG
    sept 5, 2021 019.JPG
     
  6. squirrelman

    squirrelman Member

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    2 each ?? :confused: i'm wondering why you think that ? it would add up to about $ 160-$200 just for parts for a rebuild.

    if i'm redoing carbs for myself i replace only the parts that are damaged or worn out and almost never need a rebuild kit. i usually use $2 viton -041 o-rings for float bowl gaskets, no problems yet. jets and other parts can be cleaned as good as new, replacements not really needed.

    12-1-17_176.JPG.855a0e6828772e377747193f47761e4d.JPG
     
    Last edited: Sep 11, 2021
  7. ridervfr

    ridervfr Member

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    So, which "stacks" did you end up using? When use the Viton o-rings, do they come formed to the shape of the bowl? Or, do you need to form them yourself? My set of carbs that sit on the shelf measure have 2 inch velocity stacks. Peace
     
  8. squirrelman

    squirrelman Member

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    i'm doing 2 sets of gen 3 carbs now (one is a '92, the other an unknown year) , and i put the same stacks back on that came on each, one long and the other has the 2" stacks like yours.

    sept 5, 2021 008.JPG

    the viton O-rings are round but fit easily into the bowl grooves. try it.
     
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  9. jethro

    jethro New Member

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    The 90 and 91 models have the longer stacks while the 92 and 93 have the shorter stacks. This was part of what gave them the hp increase on the later models.
     
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  10. ridervfr

    ridervfr Member

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    Interesting, I have a 91 that is titled as a 91 but has the 92 granite blue body colour. I have a 93 that I got a used set of carburetors for and quite frankly, I don't know if they are the 2 inch or longer ones. I can tell you that the 91 gets up to top speed faster than the 93, but the 93 sounds better than the 91 due to the Yoshimura slip on I have. Now, whose on first? I don't know whose on first, Whats on second. see yahz
     
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