95 GS Carb Issue?

Discussion in 'Airheads' started by Ray R, Jul 4, 2013.

  1. Ray R

    Ray R Long timer

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    I took my new-to-me 95 GS out for its maiden voyage, and I think I may have a carb jetting issue. The bike came from Denver (mile high), and I live in Oregon (162ft). I was thinking maybe old gas, but it was from November...a while ago...but not THAT long. The symptom is the bike stutters badly when I twist the throttle more than about 1/2 turn at @ 3300 rpm or above. It starts fine, idles fine. I asked the previous owner if the bike had been rejetted for his altitude, and he hadn't had any carb work done. It ran fine for him. It only has 34k miles on it. Maybe a dumb question, but do CV carbs need rejetting for altitude changes? Or should I be looking at some other cause?
    #1
  2. Airhead Wrangler

    Airhead Wrangler Long timer

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    Torn diaphragm(s). If not, remove your main jet 'carrier' along with the atomizer bits and make sure everything is nice and clean and not plugged up in any way. Verify that you have the stock mains in there which should be 135s for your bike.
    #2
  3. disston

    disston ShadeTreeExpert

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    You have not ridden far enough to use a full tank of gas and think there may be jetting problems?

    Add some fresh gas to that old gas. Use high test for awhile (high test cleans better) Consider that these machines get regular maintenance. That includes changing all the fluids on a schedule much shorter than modern machines. These machines do seem to do best when using the fluids they were designed for.

    Tune ups need to be performed on a regular schedule. Plugs, wire, air filters and assorted items may be due for change. New fuel line is an often neglected expense because we don't use the 79 cents a foot variety. Filters may help but I use only the stock screens in the tank.

    Then there is carburetor tuning and rebuilding. You have to learn to take the carburetors off the bike and replace them with out breaking them. The act of removing and replacing all the jets after cleaning will lead to the discovery of broken O-rings. The large rubber diaphragms can have holes causing problems. Careful when you venture into this that you don't mix up the parts side to side. Usually best to do one carb at a time. Fot a beginner carb rebuild do not take the throttles or the enrichners apart. Do replace the enrichner gasket and use Blue Loctight on the 4 enrichner screws.

    Beings as this bike came from mile high Denver and the '95's were probably lean jetted somebody may have changed jets. See what jets there are and make sure the jet needle is in the correct position. The jet needle for this model is 3 clicks. That is 3 slots in from the top.

    There are also model numbers for these carbs. See if the right ones are there. For 1995 R100GS the carb numbers are 64/32/357 & 358

    Have many miles on this bike?
    #3
  4. Rob Farmer

    Rob Farmer Long timer

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    I had a richness and stutter issue on my 93 100PD. Turned out to be the o rings under the slides had swelled up to almost twice their normal size due to ethanol in the fuel. The previous owner had bought a rebuild kit from Motorworks so the chances are their kit came with a pair of O rings that weren't ethanol friendly.

    I'm not saying this is definitely the issue but it's worth checking

    Part 22

    [​IMG]
    #4
  5. Ray R

    Ray R Long timer

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    Thanks, guys. If I'm cruising along at 50 mph and @3k rpm and crank the throttle, it simply won't pull. It's like it's starving for air or fuel or both. I also tried it with the choke closed, and it was worse. From your responses so far, it sounds like it's more likely a carb maintenance issue rather than jetting. And it sounds like I'll need to tear into the carbs to find out. That'll have to happen another day when time allows. Thanks again for the responses.
    #5
  6. bajaburro

    bajaburro Ancient Adventurer

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    if you going to own an air/head your going to have to get familiar with those carbs as is taking them apart for a look see.
    #6
  7. disston

    disston ShadeTreeExpert

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    I do not understand the comment, "also tried it with the choke closed"???

    The choke or more correctly the enrichners are used for starting and cool weather warm up. Then they are off. They have no function or reason to be on after the engine is close to warmed up.

    The chokes are closed when the bike is warm so they should be closed already? Or you tried to drive with the chokes on as a test of sorts?

    I think what may be going on is that you expect this bike to run like your 2010 Nissan, or what ever is the current set of wheels. The modern fuel injected computer controlled variable valve timing multi fuel machine has nothing to do with how an Airhead works. #1...warm the engine up. If it's not cold out you may drive off with the chokes, enrichners, partially engaged. But you will not be investigating how the carbs work till the bike is warmed up. Usually about 10 mins of ridding brings the engine to operating temp.

    Carbs are suspect #1 but the timing and the valve lash settings are also going to have to be checked. The on board tool kit has enough tools to set the valves if the tool kit is complete enough. Check a Clymer's or Hayne's manual for the valve lash procedure.

    Ignition timing should be checked at full advance and you need a timing light for this.

    After everything is checked and put into standard adjustment then it may be time to rebuild the carbs.

    Do you have a Clymer's or Hayne's manual? How many miles on this bike?

    Give us some history of this bike if you can. History if known before you got it and history of your ownership, use.
    #7
  8. Ray R

    Ray R Long timer

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    It's all in the first post. I took a 30 mile ride and discovered the issue. The previous owner in Denver owned it since 2000, and the only issue he ever had was a diode board that needed replacement.

    I know the fueling is not computer controlled. I don't own a Nissan.
    #8
  9. Stagehand

    Stagehand Imperfectionist

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    I'd also just pull the carb tops for a look see at the diaphrams. Def sounds like a torn one.
    #9
  10. squish

    squish Out of the office.

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    First, I would drain all the gas from the fuel tank,
    Fill with normal regular
    Before starting the bike again pull the tops of the carbs and check the diaphragms and pull the float bowls and check for nastyness. Clean fix or repair anything you found.

    When you say closed choke, do you mean with the choke lever in the "on" or cold start position?
    Or do you mean in the off position, as in normal running position?

    Winter gas is nasty, and at least here I. Ca gas goes off quick especially if you mix it with a bike that is parked in a humid environment. Because the good flammable stuff kicks off out of the gas and water gets into the gas.
    If the gets run though the carbs they get clogged up right quick and run like crap down low in the rpm range.
    #10
  11. Ray R

    Ray R Long timer

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    I'm starting to do some digging. Diaphragms look fine. Going to check the needle position later. Clymer says the needle should just gently pull out. Mine doesn't. But I have a screw in the center of the piston (looking from the top) that I believe holds the needle in place.

    On the parts diagram above, I don't have o-ring #22. Max parts fiche shows it on the diagram, but doesn't list a part number or price for it. Maybe that's an earlier model?
    #11
  12. Solo Lobo

    Solo Lobo airhead or nothing

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    With the fuel lines disconnected from the carbs, open the taps and blow through the lines into the tank.

    If it seems like there may be some resistance, it is possible that the filter screens on the petcocks are clogged.

    Alternately you can pull the petcocks and check the screens.
    #12
  13. darklight79

    darklight79 drink it , ride it , nail it

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    Also get some starbrite ethanol smurf piss enzyme works to combat ethanolazation
    #13
  14. _cy_

    _cy_ Long timer

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    lots of great info has already been give above ... have you resolved this issue yet?

    symptoms you are describing can be caused by a variety of reasons. don't assume they are not mechanical and/or electrical issues.

    fuel mixture on Bings are controlled by a combination of needle/jet holder, max fuel flow controlled by main jet and low speed circuit screw.

    notches on needle determines how fast fuel is dispensed as piston goes up. fuel profile is leaner as needle is dropped downwards. so normally needle is dropped a few notches to lean down for altitude.

    A CV carb will compensate a limited amount for altitude as air gets thinner. but cannot effect max fuel flow rate. which is controlled by main jet.

    best to return all settings, including main jets to factory setting for your bike as the best starting point.
    #14
  15. supershaft

    supershaft because I can

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    CV carbs compensate nothing but the throttle at altitude but they do that at sea level too. Crack the throttle wide open from idle at seal level and the slide (the actual throttle) will lift only so high until the engine can actually use full throttle (the slide all the way up). Do the same thing at altitude and the same thing will happen only this time the slide won't lift as high because there isn't as much air to suck in. You can do the same thing with your wrist with a slide carb. All it takes is paying attention to your engine's needs and refraining from giving the engine too much throttle. All that does is bog it down. Jetting? CV's do not compensate jetting. What they compensate is throttle input.
    #15
  16. _cy_

    _cy_ Long timer

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    sorry but you are dead wrong .. Bing CV carbs compensate to a limited amount for altitude. thickness of air changes speed piston raises, which changes fuel release profile. compensating a limited amount for altitude. this is why folks will drop Bing needles a couple of notches to lean out mixture profile for altitude.

    piston going up or down controls fuel mixture on the fly, until piston reaches max opening. once full throttle has been reached, main jets takes over. diafram controlled piston then has no further effect until air velocity decreases.. allowing piston to travel downward.

    above is old news and well established ..... why are you still denying this?
    #16
  17. boxermoose

    boxermoose Regressive airhead

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    If the PO never touched the Carbs then after 18 years it's worthwhile going thru them with the basic Bing rebuild kit and diaphragms

    Doesn't take long, isn't hard and is well worth it. While you are at it get a new set of jets

    Take the model # direct off of the carbs as you'll need it to make sure the right kit is ordered

    http://www.bingcarburetor.com/service.html
    #17
  18. supershaft

    supershaft because I can

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    What folks drop jet needles a couple of notches for altitude?

    Why am I still denying what? A slide carb does exactly what you are describing and it isn't a CV carb. The only difference is a slide carb takes some brains to use correctly and a CV not so much. All the while the jetting remains the same in BOTH type carbs. Or put another way: OK, a CV compensates jetting at altitude but so does a slide carb if you just apply less throttle. It is the same difference.
    #18
  19. Ray R

    Ray R Long timer

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    Diaphragms check out ok.
    Needle position....3 from top....check.
    Main jet is 135...check.
    Float bowls are clean...check.

    Draining gas now.......
    #19
  20. supershaft

    supershaft because I can

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    When do the floats shut off the fuel flow?
    #20