F650GS wont start in cold weather

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Thread: F650GS wont start in cold weather

  1. #1
    Bike
    K1100RS, F650GS
    Join Date
    Mar 2013
    Location
    Parys, South Africa
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    56
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    Default F650GS wont start in cold weather

    Hi Folks,

    It’s been eons since I posted on the forum. My F650 just runs, and runs, it’s been utterly reliable with one exception. It’s had the cold starting problem for a couple of years, when the temperature drops below about 10 deg c it won’t start till the temperature is at least 15 deg c.

    I live in SA, in a small farming town in the Free State, we’re going into winter and the old problem has started. This year I’m determined to figure it out.

    My bikes a 2004 twin spark with close to 100,000kms on the clock and I’ve given the old girl a serious service and hoped to find the cause. But no luck as yet.

    I’ve read a number of posts about the same problem, and checked everything mentioned.
    Hitting the starter button she cranks strongly but doesn’t fire up. If I continue to crank the engine you’ll hear it firing and the cranking speeds up but the sticks don’t seem to catch. Opening the throttle and I get a backfire through the throttle body. Squirting some engine start into the throttle body makes the motor fire up until spray has been burnt, then it stops.

    Hitting the starter at lunchtime when it’s warmer, she’ll fire up in a heartbeat and idle purrrfectly. And ride superbly on the road.

    This what I’ve been through in the last week……….

    Valve Clearance: Checked them, all four are within spec

    Battery: Brand new Motobat, it was replaced last week and has been kept charged whilst I fiddle. Leaving the charger on overnight didn’t help. In fact adding
    jumper leads to the car didn’t help. The terminals are nice and tight.

    Throttle body: Was removed and cleaned, the rubber seal to the head adapter is perfect, no cracks for leaking air. The same goes for the rubber adapter between the head and the throttle body.

    Throttle position sensor: I removed it and checked with the multimeter. It’s just a 3 terminal pot and it checked out OK. The socket side checked out OK, it has 5.00v on the two outside terminals.

    Air Temp sensor: I checked its resistance to a table of ohms / deg c. I checked it at body heat, in the fridge, and the freezer. Its resistance was very close to the table. The socket has 5v when disconnected. This morning I connected a 5.6k ohm resistor in place of the sensor, this would trick the computer into thinking the air is about 26deg c, it had no effect, it just cranked.

    Idle Control Valve: This was removed and cleaned with carb cleaner. It had only a snifter of black deposit on it. When the ignition is switched on the plunger moves in and out. And when the bike runs, the idle is perfect.

    Water Temperature Sensor: I’ve not checked anything here. When the bike runs and is left idling the fan cuts in and out.
    Injector: It puts out uniform spray of fuel when cranked.

    Spark Plugs: They were replaced last winter. They’re like new, the electrodes are clean, with no deposits. The gap is correct and hasn’t been touched since last year.

    Oil: The oil is brand new, it’s regular car 20/50, and we have little choice living in the sticks. I’m aware the oil should be thinner, but the motor does crank strongly and it’s not as though the crank is sloshing around in cold treacle with it being a dry sump. Also I cannot see the oil viscosity changing significantly in 3 hours as the air temperature rises from 5 deg c to 15deg c.


    Edit: Since posting yesterday I've been able to check the compression.

    Valve lifter active = 40psi (275kpa)
    Valve lifter disabled dry cylinder 180-210psi ( 1240-1450kpa)
    Valve lifter disabled wet cylinder 190-210psi (1310-1450kpa)

    The compress seems to be excellent for the age of the bike.


    The bike has plenty of power when running, idles perfectly at 1500rpm, and give me around 3.5l/100km so it seems once it runs everything is spot on.

    One thing I’ve noticed when I keep cranking the motor on cold morning, if I open the throttle it often back fires into the throttle body, I’m sure of this because the air box is still disconnected and I’ve seen the yellow flame. Initially I thought I was onto something as the inlet valves should be closed when it fires. Correct me if I’m wrong, but I believe the ignition sparks every revolution and the backfire is caused by unburnt fuel in the cylinder after exhaust stroke.
    That’s everything I’ve checked and found nothing which might cause the issue.

    Can anyone suggest anything I’ve missed? I’ve totally run out of ideas.
    At the moment I see the only solution is to move nearer to the equator to avoid winter.

    Regards
    MalcolmT
    Last edited by Malcolmt; 16-05-2020 at 10:34 AM. Reason: Added compression test info
    A bike on the road is worth two in the shed, wise words from Ogri

  2. #2
    Bike
    K1100RS, F650GS
    Join Date
    Mar 2013
    Location
    Parys, South Africa
    Posts
    56
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    Default

    After a chat with a buddy, I looked a deeper at the engine temperature sensor. Apart from controlling the fan, this sensor controls fuel mixture when the engine is stone cold. Yesterday afternoon after I’d run the engine for a minute, the sensor measured 2k ohm, the engine could have been around 25-30deg c. This morning it was 5k ohm at maybe 5deg c.

    It didn’t fire when I tried to start it up, but putting a 10k ohm resistor in the sensor connector to simulate a colder engine made it fire a little. Changing it to 33k ohm and the bike started.

    It looks like the engine doesn’t start in cold weather because it’s not getting enough “choke”. This might be the reason so many people have cold stating problems.
    Does anyone know where I can get ohms / temperature data on the sensor ? This will help me decide if the sensor is faulty. I’ve found a lot of equivalent sensors suggested but none of the suppliers give info on the sensor curves.

    Cheers
    Malcolm
    A bike on the road is worth two in the shed, wise words from Ogri

  3. #3
    Bike
    05 Dakar
    Join Date
    Dec 2006
    Location
    Ombersley, Worcs
    Posts
    1,183
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    It sounds like you’re nearly there with it but a GS 911 would probably give you a fault code. Might be easier than just changing parts out.

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  5. #4
    Bike
    K1100RS, F650GS
    Join Date
    Mar 2013
    Location
    Parys, South Africa
    Posts
    56
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    Default

    Hi Dansin,
    Yes, I've definitely made progress in the last day.
    I'm in a small farming town about 130km from the nearest dealer in Jo'burg, and with our lock down I'm unable to get there.
    We've got two bike dealers in town, their mechanics are youngsters who specialise in fixing Chinese scooters, I'll avoid them.

    With the bike not starting from a stone cold engine there's only a short window to work, once its run for a minute it starts perfectly.
    A dealer would need to keep the bike for a few days, leave parked in their yard, and check it before the sun comes up. That won't happen.

    The engine temperature sensor appears to have a problem at low temperatures but works OK when the engine is hot... the fan comes on nicely.
    For this reason I don't have much faith in a diagnostic tool checking the sensor.
    I'd swap the sensor but they're quite pricey over here, I avoid the poke and hope fault finding technique, plus my mom was from Yorkshire, enough said there.

    The same sensor has been used on lots of BMW cars since the mid 90's, and data on the temp/ohms curve will be a great help to verify if the sensor is OK.
    None of the manufacturers include the curves in their specs.

    I'm going to search BMW classic car forums, someone just might have the curves.
    The info will also help other GS owners should they get bitten by the same problem.

    Regards
    Malcolm
    A bike on the road is worth two in the shed, wise words from Ogri

  6. #5
    Bike
    05 Dakar
    Join Date
    Dec 2006
    Location
    Ombersley, Worcs
    Posts
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    Have a look on Wayne’s Crossroadz site, it may have the information you're after - https://f650gs.crossroadz.com.au/

    Or send him a PM - WayneC

  7. #6
    Bike
    K1100RS, F650GS
    Join Date
    Mar 2013
    Location
    Parys, South Africa
    Posts
    56
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    Thanks.
    I had a good browse around his site before my first post.

    I'm putting the bike down for a few weeks, I'm getting behind on chores whilst we're on house arrest, and the ol girl is getting pensive they'll not be done.
    But also in a few weeks our min temperature will have dropped making diagnosis more relevant.

    Cheers
    Malcolm
    A bike on the road is worth two in the shed, wise words from Ogri

  8. #7
    Bike
    dakar 05
    Join Date
    Sep 2013
    Location
    Serbia
    Posts
    16
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    Hi, you may wish to check and clean the injector, too. easy and short job, ticking off another suspect..


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