Carb problems with my 2nd Gen?

Discussion in '1st & 2nd Generation 1983-1989' started by slowbird, Sep 9, 2010.

  1. malaguchi

    malaguchi New Member

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    It would be a good idea to look over the choke system when the tank is off. To be sure all choke valves are closing and that all 4 are in sinc, opening fully, and that the mechanical system that operates them has nothing loose, or binding , etc. With the bike not running operate the choke and study its elements.
     
  2. rustedroot

    rustedroot New Member

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    That's my first guess due to both 1 and 4 cylinders running rich. They are only connected through the choke linkage/circuit.
     
  3. slowbird

    slowbird Member

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    ^^ That would make sense since I could only use the choke for about 10-20seconds before having to stop and switch to holding the throttle open (at around 1500rpm) with my hand.

    After about a minute the bike would be ok to idle on it's own. The choke definitely doesn't do it's job when it's time to start the bike come chilly mornings/evenings.
     
  4. squirrelman

    squirrelman Member

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    IMG_1069.jpg IMG_1072.jpg

    Dedication ?? I rode 22 miles in the rain to the shop and 22 miles back in the rain so i could work on your bike yesterday, Matt.

    Anyway, after checking that the choke cable was working fine and the plungers moved freely in and out, i loosened the clamps and had the easiest time EVER removing the carbs, thanks to the new mounts. Then i noticed that the mounts were not correctly installed with the groove at the 12 o'clock position so that it meets up with a tab on the carbs and locates the clamps for easy access. No big deal; i'll fix it. (Grooves that need to be in the straight up position are outlined in photo with pink paint marks.)

    Next, i found the only difference between US and Canadian carbs: the idle mixture screws (all set between 2 1/4 and 2 1/2 turns) have no limiter caps and a broader screwhead than US models.

    Vaccum slides move easily up and down and give the proper resistance and exactly the right "kawooooosh" sound that shows diaphrams are OK. I won't be going in there unless later testing shows that some needle shims are a benefit.

    Found carbs immaculately clean and tidy with all stock jetting.

    One float ( and maybe that needle and seat set) appeared to have been replaced.

    Inlet valves are marked 2.4, while i believe stock originals were 2.6 or 2.7, and that would indicate that they're replacements. This might need further investigation and research cuz if the needles are any fraction of a mm longer or shorter than originals, then that could effect fuel level in float bowl.

    Float heights measured about 8mm and varied about +/- 1mm.

    Close inspection of float needles showed an unusually large wear ring impressed into the rubber, so they may need replacement.

    A thin wire was poked through the slow jets to be certain the hole was open and all were the same. I have seen cases where jets looked clear but had trouble passing fuel, so i always tickle them with wire.

    Next step will be to remove slow mixture screws--since you said they hadn't been touched--and blow out passages with carb cleaner and compressed air.

    So, no real smoking guns or obvious flaws to report before continuing work to adjust and reassemble carbs before road testing.

    I'll be going over the valves next, as you requested, and will report.
     

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    Last edited: Oct 7, 2010
  5. slowbird

    slowbird Member

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    I never questioned your dedication Squirrel. I know you're committed.
    The weather has been pretty crappy hasn't it.

    Glad to hear the carbs aren't giving you any trouble. Too bad there isn't anything obviously wrong with it so we could narrow down my problem.

    When you removed the Tank did the fuel stop flowing with the fuel switch turned to the off position?
     
  6. squirrelman

    squirrelman Member

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    Petcock seemed to shut fuel off OK, but when open flows very slowly--a problem i've seen many times on my own '86 VFRs and don't understand because sometimes it flows in large volume ! (Flow testing done with filler cap open and tank 1/2 full.)

    I'll be investigating but don't expect much cuz i've been following this problem for 20 years, as long as i've had an '86 !!
     
    Last edited: Oct 7, 2010
  7. rustedroot

    rustedroot New Member

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    Service manual says if the fuel flow is restricted, drain the tank, and clean the "Fuel Strainer".

    Also, check the vent hole of the fuel filler cap for blockage....(not likely an issue since you checked flow with the cap open)
     
  8. slowbird

    slowbird Member

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    I don't think it's something that needs to be looked into at this time.

    Bike is running Rich....poor fuel flow doesn't sound like a possible cause.
     
  9. malaguchi

    malaguchi New Member

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    From my owners manual for my 1986 VFR700f: Automatic Fuel On-OFF," With the fuel valve set to on (or reserve) fuel flows to the carburetors only when the engine is being started or is running. A diaphragm shuts off fuel flow when the engine is turned off."

    In Slowbirds post # 97 he mentions turning the fuel valve to off when not running due to continued leakage. I would think it would quit leaking when the fuel level fell below the leak if the diaphragm was doing its job and not supplying more fuel when not running but in the on position.

    I do not know where the diaphragm is. Does it have an electrical connection that could be corroded, or is the diaphragm within the fuel pump and forced open by the fuel flow of the pump. I had a problem with the output side of my pump being gummed up from the bike sitting with fuel & no use.
     
  10. squirrelman

    squirrelman Member

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    Read carefully and use logic: there is NO diaphram in the petcock of an '87/'87. No vaccum or electrical diaphram.

    Fuel flows to carbs only when fuel pump is operating and when petcock is set to run or reserve.

    As for Slowbird's leak, a float bowl cover was installed poorly, and that leak has been fixed without any new gaskets.
     
  11. squirrelman

    squirrelman Member

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    Ok, Matt, i buttoned up your bike last night after some valve adjustment and carb reassembly and rode the bike home from the shop to check things over. I think you'll be pleased cuz the 4-5000 problem is gone, and the bike runs great !!!! Of course, because it was dark i didn't feel like testing it fully, so i only touched 160 km/hr briefly, but this bike would easily pull to redline in top gear i believe.

    Did a short 3 mile test before i left the shop and made some mixture screw adjustments based upon plug colors after that ride.

    I'll be examining the plugs again after riding your bike today and possibly doing some tweaks until i get all the plugs looking like they should.
     
  12. slowbird

    slowbird Member

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    That sounds great! Definitely good news! With all the nice weather happening I'm eager to ride again, but I'm more than willing to give you all the time you need to get it as good as you can get it. :smile:

    Was it the float bowls that were leaking?
    I'm guessing you got the float bowl gaskets in that you ordered? Did you get any part #'s for them for Dookie's thread?
    http://vfrworld.com/forums/1st-2nd-generation-1983-1989/32577-problem-86-vfr750fg-float-bowl-gaskets.html
     
  13. invisible cities

    invisible cities New Member

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    A good mantra for sure!
     
  14. Bernieswanson

    Bernieswanson New Member

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    Fuel leak

    Restoring my 86 VFR, I had a fuel leak also. Turns out it was from the top of the carb. Bad O-rings on the plastic T-s that feed both sides. It ran down the carb which made it seem like it was the bowls. You can't ID the leak without taking them off and by the time they were off, the gas was gone. Cost me $4 to fix. Also replaced the float needles and still had problems. Turned out to be the little filters fell off in the carb. So I put the old ones back it and it worked fine. My petcock also had to be replaced. It was really the 3 connected o-rings, but you cannot purchase just them so I had to buy the whole assembly. About $40.
    I bought a new one of these bikes back in 1986 and recall that I did my own valve adjustments and it was not that difficult. I just followed the instruction in the manual. I did buy the special tools for it though. The wrench, the holder and the screwdriver, but you could do them without the special tools. I do hope you get it all worked out. I got pretty intimate restoring this bike to pristine shape. It was worth it.
     
    Last edited: Oct 8, 2010
  15. squirrelman

    squirrelman Member

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    After riding about 45 miles round trip, i checked plugs again and found obvious improvements.

    But i guessed that the darkest plug needed further improvement, so the carbs came off again, and since i wasn't getting what i needed from the idle speed mixture screw, i tried resetting the float on that cylinder just slightly to lean the overall mixture.......and had EXCELLENT results, with increased throttle response and better power in the 4-5000 range.

    The fuel tank has been off about 6 times, the carbs off and apart 3 times, and plugs out at least 6 times, and sometimes that's the only way to tune if you don't have a dyno.
     

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  16. slowbird

    slowbird Member

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    That's amazing Jerry. You've definitely out did yourself.

    The work you've done to get these carbs running right is something I never could have done myself. (having no carb experience)

    I look forward to seeing the "Come get your bike" e-mail from you.
    Again....no rush. You just e-mail me when you're ready.
     
  17. squirrelman

    squirrelman Member

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    .........................

    After hours of tuning and experiment i've got the plugs all looking about the same, but one is still darker than the rest, so i'm not yet finished !

    The bike is running better every day, and being able to ride it and study tuning results has been key to refining it.

    Synch photos are BEFORE (bottom) and AFTER (top).
     

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    Last edited: Oct 11, 2010
  18. tinkerinWstuff

    tinkerinWstuff Administrator Staff Member

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    what's the compression readings and crankcase pressure like? seems on a 30yr old bike, there's ample opportunity for the discoloration to be due to slightly worn rings?
     
  19. slowbird

    slowbird Member

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    The guy who worked on the bike before said they were all around 170
     
  20. squirrelman

    squirrelman Member

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    Your bike is ready for pick up on Monday or anytime after.

    As a test of the work i allowed my neighbor Mark,, "rusted root, " to ride your bike on a short ride, mostly because he's a mature, responsible adult, hadn't been drinkin, i'm willing to assume moral and financial responsibility for the health of your bike, and cuz he has lots of current miles riding his '86 750 and thinks it's running great.

    He was nearly speechless when he returned and said your bike was far more "crisp and powerful" than his own, and that's the endorsement i hoped for.

    (For reasons mysterious i'm having trouble posting photos here.)
     
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