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Thread: Is this normal with cold weather? Cold start idle problem

  1. #1
    Registered User helmut_head's Avatar
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    Is this normal with cold weather? Cold start idle problem

    Question for perennial owners.

    My '83 R80RT has suddenly decided to have cold start issues, where I need to dial back the cold start choke from 100% to about 75%. Normal? Synch issue? Or just a cold weather thing?

    Happy to say I got to ride about 175 miles this weekend, regardless...in Michigan.

    Thanks!

    HH
    Helmut always wears a Helmet.

  2. #2
    Registered User toooldtocare's Avatar
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    Sounds like my current and past bikes. In the summer they would be able to come off choke almost immediately, but in 30's I have to leave them on reduced choke for a few minutes. Dyna III helps though to light it off.

  3. #3
    Registered User donbmw's Avatar
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    Sounds normal to me also. Have been riding Airheads since 82 and that is the way mine are. Will need the choke on a little longer in cold weather.

  4. #4
    #4869 DennisDarrow's Avatar
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    Are you saying that to start it, when you first turn it over that you have had to change from 100% engaged to 75% in order for it to start and in the summer you had to be at 100% ........OR............after it starts you move from 100 to 75%???????????????

    If the latter.......it should be this way all the time.......otherwise if you start at 100% in the summer but 75% now....you have a problem......God bless......Dennis

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    Registered User lkchris's Avatar
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    Reason any gasoline engine (probably less for direct fuel injection) needs "choke" is because the fuel in the fuel/air mixture tends to adhere itself to the cold metal of the intake tract and not make it into the cylinder to be combusted. "Choke" simply increases the chances some makes it by making the mixture richer.

    Warm up is obviously slower at cold temperatures and this both because metal is cold and incoming air is cold. Granted the airhead engine has a VERY short intake tract, but there's still some there.

    Concurrent with providing the extra mixture is the need for a little extra throttle to actually keep the motor running in this condition. Airheads have nothing to correspond with the old "fast idle cam" on carb'd cars or the "cold start valve" on FI cars, so the rider needs to turn the throttle a bit to provide this extra air to facilitate starting and intitial running. BTW, the purpose of the "choke" control on the early K-bikes and Oilheads was simply to accomplish this, as it did nothing but activate fast idle--the rich mixture created electronically.

    Me thinks if you could achieve a faster idle (throttle screw?) you could shut off choke probably as quickly as you do in summer. You don't want any vacuum leaks for sure.
    Kent Christensen
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    Quote Originally Posted by lkchris View Post
    Reason any gasoline engine (probably less for direct fuel injection) needs "choke" is because the fuel in the fuel/air mixture tends to adhere itself to the cold metal of the intake tract and not make it into the cylinder to be combusted. "Choke" simply increases the chances some makes it by making the mixture richer.

    Warm up is obviously slower at cold temperatures and this both because metal is cold and incoming air is cold. Granted the airhead engine has a VERY short intake tract, but there's still some there.

    Concurrent with providing the extra mixture is the need for a little extra throttle to actually keep the motor running in this condition. Airheads have nothing to correspond with the old "fast idle cam" on carb'd cars or the "cold start valve" on FI cars, so the rider needs to turn the throttle a bit to provide this extra air to facilitate starting and intitial running. BTW, the purpose of the "choke" control on the early K-bikes and Oilheads was simply to accomplish this, as it did nothing but activate fast idle--the rich mixture created electronically.

    Me thinks if you could achieve a faster idle (throttle screw?) you could shut off choke probably as quickly as you do in summer. You don't want any vacuum leaks for sure.
    really? i always thought you needed choke in cold weather due to cold air being denser, with a resulting higher concentration of O2 molecules per volume of air. the choke then provides a richer mixture to matchup to that denser/leaner air.
    Ride Safe, Ride Lots

  7. #7
    Registered User helmut_head's Avatar
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    Quote Originally Posted by DennisDarrow View Post
    Are you saying that to start it, when you first turn it over that you have had to change from 100% engaged to 75% in order for it to start and in the summer you had to be at 100% ........OR............after it starts you move from 100 to 75%???????????????

    If the latter.......it should be this way all the time.......otherwise if you start at 100% in the summer but 75% now....you have a problem......God bless......Dennis
    Dennis,

    You got it. In summer- 100% choke to start and maintain idle. Certainly I could turn the choke down fairly quickly. Colder weather it can be started at 100% but it sputters until I turn it down to 75%. I will resync after push rod seal replacement anyway. We'll see how it responds.

    Thanks!

    gjh
    Helmut always wears a Helmet.

  8. #8
    keelerb
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    Quote Originally Posted by bikerfish1100 View Post
    really? i always thought you needed choke in cold weather due to cold air being denser, with a resulting higher concentration of O2 molecules per volume of air. the choke then provides a richer mixture to matchup to that denser/leaner air.
    If that were true, you'd keep the choke on constantly while running in that cold dense air, no?

    Too, the fuel's going to be denser when cold, so probably a wash in that regard.

  9. #9
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    Quote Originally Posted by BrianK View Post
    If that were true, you'd keep the choke on constantly while running in that cold dense air, no? As engine heats up, that temp would act to warm the incoming air so that the engine no longer needs the choke to run properly.

    Too, the fuel's going to be denser when cold, so probably a wash in that regard.
    i had a SAAB 96, carb'd, years ago. it had a movable plate that could be used to divert warm air from the exhaust manifold to preheat the air going into the carb to help bring the car off choke earlier, and to maintain a warm intake tract.
    (some of this is scientific conjecture on my part. i even went and spoke to one of our Science teachers here to try to get a better handle on this, but he was unsure as well.)
    Ride Safe, Ride Lots

  10. #10
    Registered User lkchris's Avatar
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    Yes, there have been all kinds of systems devised to speed up heating of the intake manifold. Remember all the hoses to the air cleaner everyone took off of '70s cars? These things turned off after the metal was heated, i.e. it was about heating the metal and after it was heated the system reverted to cold air intake through the snorkle.

    My Dad was a GMC truck dealer in the '70s and lots of our genius customers would turn the top of the (round) air cleaner over, exposing the filter just beneath it, consequently defeating both the initial hot air intake and then the later cold intake, i.e. they were wrong twice.
    Kent Christensen
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    '12 R1200RT, '02 R1100S, '84 R80G/S

  11. #11
    ABC,AMA(LIFE),MOA,RA,IBMW MANICMECHANIC's Avatar
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    Also remember that the engine runs on fuel vapor, and with lower temps there is less vaporization. More raw fuel will enhance the amount of vapor in the intake tract.
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  12. #12
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    Quote Originally Posted by BrianK View Post
    If that were true, you'd keep the choke on constantly while running in that cold dense air, no?

    Too, the fuel's going to be denser when cold, so probably a wash in that regard.
    i got thinking about that this morning. the fuel, being a liquid, is already denser (moelcules closer together, and moving slower) than the air. Given that status, it likely has less room available for more compression, so probably not an equal "washing" going on. tho i could be wrong in that theorization too.
    Ride Safe, Ride Lots

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