CB700SC carb cleaning

Discussion in 'The Rockies – It's all downhill from here...' started by Ricardito, Apr 10, 2012.

  1. Ricardito

    Ricardito Been here awhile

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    Gents,
    I just brought home a very very nice 1984 Honda Nighthawk, CB700SC, bought from the original owner with only 6,030 miles. It's not been ridden much for the past few years and as a result it will hardly run unless partially on choke. Carbs need cleaning and, though I suppose I could do it, I'd rather have a pro who does it frequently tackle the job. Who can you recommmed that is experienced, reliable and trustworthy in the Boulder/Longmont area? I'd rather do it myself than have the bike disappear into the backroom of some dealership for several days. If you can personally vouch for a good tech, please let me know.
    thx
    #1
  2. MrBob

    MrBob Certified Geezer

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    Great bike Ric. I had one and loved it. There is a guy who lives in Longmont and advertises on CL, something about Professional Carb work.
    http://fortcollins.craigslist.org/mcd/2943605734.html
    I don't know anything about him but you could check for any reviews on Yelp. Otherwise, Epic Motorsports. They did a good job on my XT carb. Their new home is next to Earth Roamers on I-25.
    #2
  3. Ricardito

    Ricardito Been here awhile

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    Thanks Bob. This is very helpful and gives me some options, but I have a question: What's Yelp and how do I access it?
    #3
  4. gtackett

    gtackett Been here awhile

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    I had the same issue with mine a few years back. A mechanic friend suggested turning the air/fuel(?) Screws on the bottom about 1 turn. You have to take off the metal plate which prevents them from turning.

    Worked for me.... hope that was enough info.

    Sent from my DROID Pro using Tapatalk 2
    #4
  5. r1200gs_chris

    r1200gs_chris Been here awhile

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    I had a 1984 650 Nighthawk. Great bike but the carbs can be a source of great frustration. There are MANY fuel passages on this bike and cleaning them requires patience. Try running a few tanks of fuel with SEAFOAM added. SEAFOAM and Nighthawks go hand in hand. Next culprit would be a vacuum leak. Check your intake boots and petcock vacuum line for leaks. Light a cigar and let the smoke drift up around the intake boots while the bike is running. A vacuum leak will suck up the smoke. NOTE: MAKE SURE THERE ARE NO FUEL LEAKS BEFORE YOU DO THIS OR YOU WILL HAVE A *FIREHAWK* :eek1 PM me if you need anymore help.
    #5
  6. gtackett

    gtackett Been here awhile

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    2nd the Seafoam. Forgot about using that, too.

    Sent from my DROID Pro using Tapatalk 2
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  7. MeterPig

    MeterPig Meh

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    Why not take them off and soak them? You could do the seafoam thing for a while and never get it to run right.
    #7
  8. Blakebird

    Blakebird r-u-n-n-o-f-t

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    If it takes choke to get it to run at low speeds, the low speed circuits in the carb are gummed up.

    An intake leak would make the idle climb.

    +1 on the Seafoam.

    #8
  9. Assfault

    Assfault Exposed Member

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  10. Ricardito

    Ricardito Been here awhile

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    Thanks to all. I'm reasonably sure it's the low speed jets that are gummed up. The right way to do it would be to soak the carbs, clean the jets and blow the passages with compressed air. Since I'm lazy and not fond of carb cleaner fumes I'll give the SEAFOAM treatment a try for starters and see if that cleans out the passages. If not, I'll have to decide whether to do it myself or have it done by one of the places suggested here.
    #10
  11. Blakebird

    Blakebird r-u-n-n-o-f-t

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  12. r1200gs_chris

    r1200gs_chris Been here awhile

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    If the Seafoam doesn't do the trick take them off an get cleaning. I don't recommend splitting them, keep them all together. After a soak flip them over, remove the floats, and then remove the jets. Get a small wire/guitar string and gently clean out all passages, jet holders, jets, and blow carb cleaner thru every opening. Slap it back together and off you go. Less than an hours work to clean them, not including the soak.
    #12
  13. MrBob

    MrBob Certified Geezer

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  14. Cheap Ryder

    Cheap Ryder Ride for enlightenment

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    I have been professionaly (getting paid by others) cleaning carbs since before the nighthawk was made. Do not just soak any old vacum piston carb set in cleaner or use the nastier carb/brake cleaner sprays. You can cause mucho problems. Take the float bowls off and clean the jets and emusifier tubes the main jets screw in to. Clean the float needles and make sure they shut off the gas. Check your diaphrams on the slides to see if they have any tears or holes. I glue up the holes with plastic and "right stuff" silicone type sealer. Check the anti backfire valves on the side of the carbs.....usaly there is one exposed but the others require splitting the carbs apart. If the one you can get to is OK the others should be. These diaphrams can be damaged by soaking in harsh cleaner.
    The shop I am now working at has a ultrasonic cleaner and and a immersion cleaner which get used on the nastier carbs.
    For those really plugged up idle or pilot jets use cheap Ryders trick.....use a metal scrup brush with the long bristles, about two inches long. lightly touch the end of a bristle to a grinder at a 45 degree angle. Then chuck up the plugged jet in your drill and spin the jet while pushing it down on your modified wire brush bristle. I have worked on probably hundreds of honda 90 carbs and other exotica in out of the way shops with no replacement parts and this cleaning method seems to work quite well.
    #14
  15. Boulder Ed

    Boulder Ed Bin Ridin

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    Excellent summary ... Soaking thes carbs intack would most likely damage lots of organic (rubber ) parts as that organic debris is what the solvents are designed to decompose. Sometimes a ittle does not hurt if it comes in contact, but you can literally see and feel the difference in rubber and plastic surfaces like float bowls that carb cleaning fluid comes into contact with.
    One might then need to buy a bunch of costly carb kits/parts and may still never find all the little orings buried deep in the things. Most of the time it is simply the pilot jet, possibly a main jet and air passages cleaning that does the trick. The pilot and air fuel mixture circuit are coupled so both need to be removed to clean all the way through that critical passage is what someone recently advised me on one I was cleaning. It worked great after that, as the carb actually responded to changes in the air/fuel mixture...


    #15
  16. eakins

    eakins Butler Maps

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    pinesol clean is the way to go
    http://www.advrider.com/forums/showthread.php?t=560117

    #16
  17. Ricardito

    Ricardito Been here awhile

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    The Nighthawk is going in to RMK on Tuesday for a carb cleaning and adjust by their tech Marv. It's worth it to me to have it done thoroughly and to have it adjusted/synch properly. If nothing else, I can be riding another one of my bikes, keep from inhaling noxious fumes and having a professional look over a new (to me) bike. Their shop rates seem reasonable enough.
    The advice and warnings from all who chimed in certainly alerted me to some of the pitfalls of doing it myself--either chemically or by dissasembling the 4 carbs.
    #17
  18. Hondo

    Hondo What if it's a Samsquamch?

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  19. Blakebird

    Blakebird r-u-n-n-o-f-t

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