airhead noob

Discussion in 'Airheads' started by scout18, Aug 24, 2012.

  1. scout18

    scout18 Been here awhile

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    Hey there folks I got this cool 1974 r75/6. It has dual plug heads and 900 jugs with high compression pistons and runs great, rides great. It just doesn't like to idle smoothly I know that there is a ton of information here covering this. BUT. Are there any inmates in the Portland Oregon area that wouldn't mind meeting up and showing me just what I need to do to sort this out? please pm me or email me jaredscout18@gmail.com. Thanks.
    #1
  2. craydds

    craydds Long timer

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    What carbs do you have? Bings? Yes, many inmates can help you. Bings (if that's what you are running) are easy to sort out.
    #2
  3. scout18

    scout18 Been here awhile

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    Yes Bings. I'm pretty handy. I have the Bings one turn out on the idle air screw and it starts easy but it's very lumpy at idle hot or cold. While I'm riding it runs well and pulls hard from all gears. Between 4000 and 6000 rpms it's smooth as glass.
    #3
  4. elite-less

    elite-less Been here awhile

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    You running points or an electronic ignition with the dual plug setup?


    .
    #4
  5. ignatz72

    ignatz72 call me iggy

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    Sounds like a balance and fine tune is in order.

    Plenty here can help with that; Portland? Dunno.

    Do you have a carb balancer of some sort or access to one (buying one wouldn't hurt).
    #5
  6. Rob Farmer

    Rob Farmer Long timer

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    Sounds like your points need looking at, they are a pain in the arse to do and end up being neglected as well as badly adjusted. Fitting a boyer is a good move, just don't buy the cheaper Boyer black box, buy a Microdigital. The cheaper unit has an analogue curve that doesn't match the engine.

    If you don't want the expense of an electronic ignition then theres a tool available cheaply to take the pain out of adjusting them --> Linky
    #6
  7. disston

    disston ShadeTreeExpert

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    I prefer the booster box instead of an electronic advance. You keep the mechanical advance OEM unit and you keep the points. If stuck somewhere because of box failure the stock points can be rewired in a mater of minutes. This is the one I have;

    http://www.dynaonline.com/skins/products/sportbikes/boosters/

    As long as the stock ignition works fine and fires evenly this unit will take the higher voltage off the points so they last a long, long time.
    #7
  8. craydds

    craydds Long timer

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    Do all the tuning things as recommended by these fabulous inmates. Old gas, water, and corrosion can easily mess up the idle circuit. I would take the Bings off, disassemble and thoroughly clean 'em. After installing and adjusting, check for vacuum leaks - that will affect idle. Points work fine; they are simple. I have the Boyer system and it has been reliable for many years.
    #8
  9. wirewrkr

    wirewrkr the thread-killer

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    I second Disston the dyna booster. It's just the best Bang for the Buck as far as ignition systems on the points style engines (especially the 70-78 models)
    If you're running Dyna Red coils because of the dual plugging you shouls already have some kind of boosting system, if not that may be the problem.
    #9
  10. Bill Harris

    Bill Harris Confirmed Curmudgeon

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    And if it is an R75/6 with "900 jugs with high compression pistons" lordy knows what has been done to it. Start out with a complete major service, check everything including the carbs and jetting. That will be a starting point unless you can get feedback from the PO.
    #10
  11. supershaft

    supershaft because I can

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    Dual plugged points HAVE to have a Dyna booster. They cook otherwise. The advance needs to be modified in order to time dual points correctly. Where is the timing at idle? OT? That could be your problem right there.

    One turn out? That is NOT the way to adjust mixture screws. Find the lean stumble point and the rich stumble point and adjust half way between. The screws are very often adjusted differently.

    Mixture screws adjusted thusly and still stumbles? Leak down test and listen for leaking valves. They will not idle right with leaking valves and I find them leaking often.

    Good luck!
    #11
  12. scout18

    scout18 Been here awhile

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    So I still need to short out one side then the other to find the stumble points then tune the idle screws for air flow I guess.
    #12
  13. scout18

    scout18 Been here awhile

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    Is there a special tool for snorting the plugs other than a spoke nipple adaptor.
    #13
  14. craydds

    craydds Long timer

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    Jeff Trapp makes a plug-shorting tool for carb balancing, and includes instructions; http://www.northwoodsairheads.com/Tools.html
    #14
  15. supershaft

    supershaft because I can

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    There is no need whatsoever to short out the plugs while adjusting the mixture screws. Just do one at a time while they are both idling. It is as simple as that. If the engine dies at the lean point, keep track of where it was and start the engine back up. Keep track of your turns as if the screw slot was a clock hour hand and set it half way between the stumble points while both cylinders are running. It could be 12 hours from stumble point to stumble point on one cylinder and and six hours on the other, for instance. It varies.

    Personally, I wouldn't short a cylinder out for any carb adjustment. There is absolutely no need to be chasing a setting while the bike is constantly getting over a flooded and fowled cylinder. That is what is happening to the cylinder that is shorted out. It takes our engines quite some time to completely get over being on the side stand. Same story with shorting out a plug. Oil and gas build up. Go figure. Good luck!
    #15
  16. disston

    disston ShadeTreeExpert

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    The shorting out the plugs has nothing to do with mixture. It is to balance the two sides by seeing that they fire evenly. It is for adjusting the idle speed. You now have dual plugged heads and would need some elaborate set up to use this method of balancing the carbs. That has been done but I think with limited results. You can also balance the carbs on just the top plugs which might work. Your best bet is finding or making a carb balancing tool. The Harmonizer has been popular lately but is out of production, it might be back, someday.

    After you have changed all the oils, and adjusted the valves, and put in new plugs, what kind of ignition is this bike running(?) Stock is just points but as SS says you should have a booster.

    I think my Beemer idles better if the mixture is on the rich side.
    #16
  17. scout18

    scout18 Been here awhile

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    I took the front cover off and I find one set of points and I see nothing that could be interpreted as a booster for the dyna coils. The right dyna coil has the spark plug wire for the top left plug coming from it and the bottom sparkplug for the right side. The left of course has the right top plug coming from it and the left bottom plug wire. Does that sound right? I'm going to look up a wiring diagram for Dyna coils.
    #17
  18. wirewrkr

    wirewrkr the thread-killer

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    That is how the plug wires should be, That way if a coil fails, you don't lose a cylinder. There's another reason, but I can't remember it right at the moment.
    Look carefully after taking off the tank for the booster. If you don't have a Booster, get one, they're cheap. I mount mine right in front of the toolbox on the bottom of the backbone.
    I've seen them mounted all over the place. It creates heat, so it needs to be in windpath of sorts.
    #18
  19. Bill Harris

    Bill Harris Confirmed Curmudgeon

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    Yeah, there is some explanation revolving about the voltage to fire under compression vs the voltage to fire NOT under compression. It is a circuitous explanation, and I took it on faith.

    One big plus about a Dyna Booster: if it dies, you can go back to a points-only ignition by swapping a couple of wires. BT,DT.
    #19
  20. scout18

    scout18 Been here awhile

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    Anyone have a picture of a booster? I don't think I have one. I only have one coil getting power from the points. Time to get out the meter.
    #20