Fellow Inmates, help a newbie get his bike running good, pleasssee.

Discussion in 'Airheads' started by Yachtie, Nov 1, 2012.

  1. Yachtie

    Yachtie Been here awhile

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    Just to be clear I took a few pics.

    I believe this is te smaller screw you speak of and this is set to one full turn out

    [​IMG]


    This I take it is the larger screw? Idle speed screw? One turn out? If its not and I'm missing a screw, what should this one be set too cause I already fiddled with it.

    [​IMG]




    #81
  2. disston

    disston ShadeTreeExpert

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    Close but no cigar. You named them correctly. The short version, Idle Mix Screw (the little one) is one turn Out, Idle Speed Screw (the big one) is one turn In.

    A longer version. The idle mix screw is regulating the amount of gas the idle circuit carries. The more out the screw is the richer the mixture will be at idle. For an R90/6 the official starting place for the little idle mixture screw is one turn out. You may adjust this some but don't do that at first till you get the speed closer to what it needs to be. Set the idle mix at one turn out. This is the adjustment in the Bing manual for all R90/6es.

    The idle speed screw provides a stop for the butterfly so it doesn't close all the way. It holds the butterfly open a very tiny amount. The two carbs are balanced with the idle speed screws. They need to be even in the sense that the two cylinders are running at the same speed and pulling the same amount. That is why it is called "balanced". Set the idle speed screws in one turn from the moment they first contact the bell crank of the throttle shaft. This is hard to do when the carbs are on the bike, the screw and the part it contacts are on the back side of the carb, so it's just hard to do. You want to try and set the speed screws to ONE TURN IN.

    The Mix Screws ONE TURN OUT.

    You need a method of balancing the carbs to get these settings even between the two sides. I'll ask again, Do you have the shorting rods or a manometer or other tool that compares carb vacuum so you can balance the carbs?
    #82
  3. Yachtie

    Yachtie Been here awhile

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    Thanks for the clarification and no. I do not have those tools at the moment.

    #83
  4. Yachtie

    Yachtie Been here awhile

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    Also, where should this throttle cable "tensioner" screw be set roughly

    [​IMG]
    #84
  5. Airhead Wrangler

    Airhead Wrangler Long timer

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    Such that it has enough free play that it allows your idle adjuster screw to dictate idle speed and not cable tension. You also need to set each side so that your throttle "picks up" both throttle shafts off the idle speed stop exactly in unison. First idle speeds need to be synced with vacuum gauges or shorting sticks, etc. The next thing that needs to be synced is when the throttle picks up both butterfly shafts off the idle stops. That's done with those cable adjusters.
    #85
  6. disston

    disston ShadeTreeExpert

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    Balancing the carbs is a very important part of making the bike run as it should and smoothly. Unbalanced the bike will get poor gas mileage, be hard to start, be ruff and vibrate and even make unnatural noises. This is the key to making an Airhead run. It is some what an Art, maybe more Art than science. That can't really be true because these are machines but it's a fact that some tuners are better at it than others and it's hard to say why.

    This is one method of balancing carbs. It involves shorting out the spark plug leads so the bike tries to run or does run on one side. You need this tool. You can buy it or you can make it yourself;

    [​IMG]

    Sorry the picture is so small. These are for sale at Northwoods Airheads;

    http://imageshack.us/a/img849/6267/thbalancetoolimg1229133.jpg

    To make a pair of these tools use a long 4mm screw from the neighborhood hardware store. The screw is 4 x .7 and should be 60 or 70 mm long. The nipples that came with a new pair of spark plugs go on one end and you will also need a 4 x .7 nut to lock the nipple on the end. Leave enough thread of the nipple open on the end so the rod can be attached to a spark plug. The head of the screw is cut off so the plug wire can be attached to it. Tighten it down a little with a wrench, it will vibrate loose if not tightened. It is important that the plug wires do not become unconnected when the bike is running. They should be firing the plugs or be shorted to ground to not fire the plugs but they should not be just unconnected, that can cause ignition problems.

    Once the bike is warm and the studs are connected with the bike at idle you short out one plug with a screw driver so the bike will run momentarily on one cylinder. Note the sound and speed of the bike on one cylinder. Take the screwdriver away and rev the throttle a little to clear pooled gas in the intake and then short out the plug on the other side. Note the sound and the speed of the bike on the other cylinder. If one cylinder is running faster than the other adjust the speed screws a little, either one side up or the other side down depending on whether you want the bike to run faster or slower over all, repeat. Do this several times back and forth till you have the idle speed you think will work and the carbs are balanced. These adjustments are made with the idle speed screws only.

    After the idle is set the throttle cables are adjusted so the throttles both start pulling at the same time. This is sometimes done with other machines at 1400 rpm or 3000 rpm. Some riders try to set the higher rpm using the shorting rods. I just try to get both butterflys moving at exactly the same moment. Note the amount of slack at the throttle cable barrel on top of the carb where the adjustment is made. In theory both cables should have the same amount of free play. If you pull on the cable sheath at the top of the carb you can see it is free till it pulls the actual cable inside the sheath. You can see the free play by tipping the sheath ends to the side until they start to pull the throttle. Anyway the free play should be even and it should be as small as possible.

    Go for a longer ride. You may have to repeat this process several times. Once the speed is stable and the bike idles you may now adjust the mixture screws a little but they should probably not be far off from the setting in the book. For your bike the book calls for 1 turn out on the mixture screw.

    Do not ride the bike for any distances with the shorting rods attached. They will vibrate loose and cause ignition problems. I think your bike has an after market ignition of some kind? This is a very important warning for these ignition systems.
    #86
  7. Yachtie

    Yachtie Been here awhile

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    thanks for all that info! very greatful.

    i fired up the bike again tonight, with the speed screws and mixture screws roughly set. Idles much better around the 1k mark.

    Went for a short ride around the block, can definitely feel that they are not balance. So need to tackle that. But on a much more gloom side, after about 20 minutes of running and riding pretty good, all things considered, the bike like before starts bogging/coughing back firing and wanting to cut out.

    So with Valves "set" (would rather have a pro make sure to call it properly set), carbs cleaned, intake rubber replaced. All that and the original symptoms still persist.

    Now timing, is my next number one priority.
    #87
  8. disston

    disston ShadeTreeExpert

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    You need to timing light to properly check timing at idle and also at 3000 rpm.

    Th problems you now report are possibly the carb balance or the timing. You can find a cheap timing light at Harbor Freight, if you don't have one, and the shorting rods will help with the carb balance.

    There are also other better methods but they also cost more for carb balance. You can find mention of an Inmates product in Vendors about the Harmonizer. This tool is the latest and greatest solution to the balance problem. It doesn't sound very cheap but actually there are more expensive solutions.

    See how you do with the shorting rods.
    #88
  9. photorider

    photorider Been here awhile

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    Did you check the sensor plate while you had the front cover off? Just try twisting it with your fingers. If it moves, that's your problem!
    #89
  10. Yachtie

    Yachtie Been here awhile

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    #90
  11. photorider

    photorider Been here awhile

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    Hmmmm...no. Different set-up. Disregard.
    #91
  12. headtube

    headtube 6 mesas de invierno!

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    Fuel flow?? When the symptoms you describe begin to occur, stop the bike and drop the float bowls. Check the level of petrol in the bowl. It should be 3/4 full, or there abouts.

    Question: does it bog and cough straight up or in corners?

    Things to look for... (1. Be sure your gas cap is venting (breathing). You can try running the bike with the gas cap not fully closed to see if this betters your situation. (2. When the bike is NOT running - open the taps on the tank without the fuel line attached. Catch the fuel in a vessel... look for bits. Fuel should flow undisturbed. If there is a trickle or bits, you've got some cleaning to do.

    If this doesn't better your problem there is a possibility that you have an electrical short that you need to track down.
    #92
  13. Yachtie

    Yachtie Been here awhile

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    thanks, i'll try that. Symptoms occur roughly 20 minutes after a start up where it sat for a while. The 20 minutes right after start up the bike runs Good. Then any time i give it any kind of throttle is starts all the symptoms and just progressively gets worse and worse to where its trying to cut out just in idle as well.
    #93
  14. Beamer Bum

    Beamer Bum Been here awhile

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    I've been following this with interest and now have to put my 2 cents in. If the bike runs good for 20 minutes before it starts acting up, you either have a heat issue like an overheating coil or, like Headtube suggested, your tank isn't venting to atmosphere. When it starts running crappy, open the fuel cap. If the tank develops a vacuum, you won't get fuel to the carbs. If you can hear the air rush in when you open the cap, it isn't venting. I think I saw you have new coils, so my guess (only a guess since I'm not there) is tank venting.

    Don't worry with the collective wisdom here, you WILL get this sorted.
    #94
  15. disston

    disston ShadeTreeExpert

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    Bike is a 1976 R90/6. The /6 bikes don't have this tank venting issue I think. I have a 1975 one and I don't know how the tanks are vented but have never heard of this issue.

    It has had a lot of modifications including an electronic crank fired ignition.
    #95
  16. Yachtie

    Yachtie Been here awhile

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    Important to note, i have a R100/7 Tank.
    #96
  17. rufusswan

    rufusswan Been here awhile

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    I don't think anyone answered your question about the cable adjuster on top of the carb. In the position shown in the last photo, with the adjuter screwed all the way down into the carb, you have maximum amount of slack in the cable.

    To take slack out of the cable, start screwing the adjuster out ( or up ) to remove slack.
    #97
  18. Yachtie

    Yachtie Been here awhile

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    thanks for that!
    #98
  19. photomd

    photomd Been here awhile

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    If the engine is running properly for 20 minutes, and you have some valve clatter, I don't think think it's the valves. You've got compression and fuel. That's why it'll start and run for awhile. Something is changing as it gets warm that causes it to run rough. I'd concentrate on what can change as the motor gets warm: carbs, carb boots, your new ignition, fuel flow and coils.

    First I'd get it warm and get it back firing and spitting. Then I'd try to figure out if it's running rich or lean: do you smell unburned fuel. If so, pull the air filters and see if it runs better. If you don't smell fuel, turn the choke on. Better with choke on? Pulling the air filter will lean out the mixture and turing on the choke will increase fuel into the engine.

    Also check your diaphragms carefully. Pulling them out and carefully stretch the rubber looking for any pin holes or tears. If you find any or the rubber is hard, replace the diaphragm and recheck. I've had a bike run exactly like this: run fine cold and progressively not be able to take any throttle as it got worm and it turned out to be a hole in an old diaphragm.

    Next I'd test for air leaks at the carbs: take WD-40 and spray it around the junctions at the front and rear of each carb and air box junction. If the idle changes, you've got an air leak. Fix it and recheck. Also spray around the diaphragm top and where the butterfly shaft is located on the carbs. These can leak too.

    To test the ignition, simply remove the new one and put the old one back on. Some electronic ignitions don't work and you need to check the engine with a good one. If this fixes the problem, get a new electronic ignition. Your timing could be off, but it should run a little rough cold as well as hot with incorrect timing. Also I don't know if your new ignition has a mechanical advance or electronic. Again, mechanical one will not change going from cold to hot. An electronic one can fail as it gets hot if there's an intermittant short the opens with heat.

    Test the fuel flow is easy. Ride for 20 minutes and get it running rough, crack the fuel fill and see if it runs better. All these bikes have some sort of fuel vent. You've got to replace the fuel in your tank with air or it won't flow fuel to the carbs.

    As for the coils, replace them with the old ones and see if the problem is corrected. Also make sure your ignition leads are the correct ones for the bike. Some run resistence leads, some don't. I don't keep that in my brain. You need a manual to help get things set up correctly.

    Do these things and let us know what you find. It sounds like a fun project. :1drink
    #99
  20. disston

    disston ShadeTreeExpert

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    All good ideas. I still think that the proper adjustment of the carbs can be at fault. I'm not sure about this. Just think you haven't gotten them right yet. And these bikes always run weird after twenty mins if the carbs aren't properly balanced.

    Do you have the timing light? You said you would move to checking the timing. That's a good one to get out of the way.

    Do /7 tanks have vents? It might say in the manual. Do you have a manual?

    I wanted to add my small bit about the cable adjusters. Throttle cables are manufactured to a certain standard so they match and will fit the application they were made for. Those standards are not an exact measure so some inner cables are a little longer or shorter, some outer cables are not exact also. The cable adjusters are here to make up for this little difference found. There should always be some bit of slack in the cables. Don't confuse with slack in the twist grip, that's there also but the cable should not pull the carb throttle while the bike is at idle. Idle is effected and adjust only by the big screw on the bottom of the carb. When you twist your wrist the cables take over and their balance comes into play.

    In theory the cables should act at the same time, they should have the exact same amount of free play. In practice this can be hard to see, or achieve. Sometimes one cable will show a definite movement when the throttle is twisted and the other cable will seem just soft.

    But check the timing and the tank vent(?) and then you'll be back at carbs again.