New member - F650 warm starting issue

Page 1 of 3 123 LastLast
Results 1 to 10 of 25

Thread: New member - F650 warm starting issue

  1. #1
    Bike
    F650 1997
    Join Date
    Apr 2020
    Location
    Bregenz, Austria
    Posts
    14
    Post Thanks / Like

    Default New member - F650 warm starting issue

    Hi All

    my name is Martin. I originally come from Devon however have been living in the Vorarlberg region of Austria since 2001. Living at the foot of the Alps I consider myself very lucky to
    have such fantastic biking roads right on my front doorstep. I have gone through a number of bike styles over the years, chopper, tourer, oldtimer, enduro, vespa, my garage currently
    consists of a GTS300 Vespa which i love to scoot about on, taxi the kids etc., last year however I had the opportunity to buy a 1997 BMW F650 Funduro (not ST version), with just
    13000Km on the clock.

    What needed fixing:

    - it had suffered a fall at some point, the handlebar was bent. Rather than risking straightening out the existing bars I just put a new TRW on.
    - The jolting under 3000rpm drove me nuts. I put a 15 toothsprocket on the front and now it runs much better.
    - Fork seals

    I now have one more problem. I have searched throughout the forums, both english and german, but still cant seem to find a fix for the issue.
    The bike is difficult to start when warm. Starting from cold, the bike requires almost no choke whatsoever, in fact any more than a few degrees of choke makes cold starting difficult.
    Better is to start without choke at all, hold the gas open a little once started, after a couple of KM the motor runs just fine. When fully warmed up the motor seems to run like
    clockwork. Very steady idle, responsive, no backfiring when driving downhill, consumption good etc. etc. Absolutely perfect running. The problem is, that when the motor is hot and I switch off, it is difficult to start again. The motor turns over fine but does not seem to fire.

    I have changed the plugs, plugcaps and leads. This has not helped. I know that the carbs were completely stripped down and professionally cleaned before I got the bike, and as I
    say, the bike runs like clockwork otherwise. While the bike was at the BMW workshop getting the forkseals done, i mentioned this issue and asked the mechanic to check the carb
    settings. He did this and measured the CO2 emmissions, all seemed to be fine. Any ideas what the cause of this warm starting issue could be? I remember reading somewhere about
    a possible compression/decompression issue, but cant find the information again.

    Any help would be greatly appreciated. If you need any further information please let me know.

    Kind regard
    Martin

  2. #2
    Join Date
    Apr 2019
    Posts
    471
    Post Thanks / Like

    Default

    It sounds like the decompressor problem but I believe this was only suffered by the Chinese made G650GS - essentially a design/manufacturing issue meant that the decompressor did not open the exhaust cam sufficiently to allow the starter to spin the motor fast enough for the ECU/BMS to trigger a spark.

    In your case, it's possible that if the decompressor cam is badly worn then then, when the motor is hot, it doesn't open the exhaust valve enough to reduce the compression sufficiently for the motor to spin fast enough to start. However, with a carb based engine, I would have thought the effect would have to be very pronounced to stop the engine starting and you would be able hear the difference in engine speed on the starter when the engine was hot compared with it being cold. I would be tempted to do a hot versus cold compression test on the engine to see whether you can see a large difference.

    The other thing to check is that the battery is in very good condition and, if necessary, try a new battery to ensure that the engine is being turned over fast enough on the starter. Normally, you shouldn't need any choke (actually an enricher cold starting device) to start the engine when hot and it sounds as though the carbs should be in good condition making it unlikely that they are the cause of the hot starting problem. The only other possibility may be an electrical problem and it is not unknown for coils to play up when hot. I would definitely check for a spark when the engine is hot and refuses to start to rule this out as the cause of the problem.
    2006 F650GS in Black
    9,300 Miles

  3. #3
    Bike
    F650 1997
    Join Date
    Apr 2020
    Location
    Bregenz, Austria
    Posts
    14
    Post Thanks / Like

    Default

    Quote Originally Posted by AWJDThumper View Post
    It sounds like the decompressor problem but I believe this was only suffered by the Chinese made G650GS - essentially a design/manufacturing issue meant that the decompressor did not open the exhaust cam sufficiently to allow the starter to spin the motor fast enough for the ECU/BMS to trigger a spark.

    In your case, it's possible that if the decompressor cam is badly worn then then, when the motor is hot, it doesn't open the exhaust valve enough to reduce the compression sufficiently for the motor to spin fast enough to start. However, with a carb based engine, I would have thought the effect would have to be very pronounced to stop the engine starting and you would be able hear the difference in engine speed on the starter when the engine was hot compared with it being cold. I would be tempted to do a hot versus cold compression test on the engine to see whether you can see a large difference.

    The other thing to check is that the battery is in very good condition and, if necessary, try a new battery to ensure that the engine is being turned over fast enough on the starter. Normally, you shouldn't need any choke (actually an enricher cold starting device) to start the engine when hot and it sounds as though the carbs should be in good condition making it unlikely that they are the cause of the hot starting problem. The only other possibility may be an electrical problem and it is not unknown for coils to play up when hot. I would definitely check for a spark when the engine is hot and refuses to start to rule this out as the cause of the problem.
    Thank you very much for your response. Here my feedback to the points you mentioned:

    - Is it realistic that the decompressor cam is badly worn? The bike only has 14000km on the clock now (nothing for a rotax). Hot or cold, I cannot hear or feel any difference in motor speed when the engine is turning over. Is there an easy method for carrying out the compression check between hot and cold?

    - The battery is a new Lithium (installed by the previous owner). For a bike like this an overkill in my opinion. The battery is fine.

    - the bike does not require choke when hot, but also not when COLD. With the other carb bikes I have owned in the past, choke was generally needed when the bike was cold. Seems strange that this is not the case with the F650. All it requires is to hold the gas open a little, within a couple of minutes she ticks along on her own just nicely.

    - Could you please explain the easy way to check for a spark when the engine is hot: remove BOTH plugs and hold the plug end against the engine block while cranking the engine? Do both plugs need to be checked? Is it possible that a spark can be too weak to start combustion? Is it worth trying Iridium plugs in your opinion?

    Many thanks once again for the tips.
    Kind regards
    Martin

  4. Remove Advertisements
    F650.co.uk
    Advertisements
     

  5. #4
    Bike
    F650(1997) & F650GS(2000)
    Join Date
    Aug 2004
    Location
    Bedford.
    Posts
    822
    Post Thanks / Like

    Default

    Vapour lock in petrol tank ? not letting fuel in carbs caused by engine heat or blocked tank vent .

    But re-reading your last post would say over-fueling as you do not need choke when cold.

    Do you turn off fuel tap ?

    Have you tried opening the throttle when warm starting ?

    You possibly need to check choke mech in carbs and float heights.

    Best to try this first turn of fuel tap and run the engine does the rpm pick up after a while if so could back up - wrong float heights or poor o ring around float valve seat.

    If it does this --- short term you could turn fuel tap off before you stop engine let it run for a minute to lower fuel height in carbs.

    Does not cost anything to try the last 2 above ideas. Let us know results.
    Last edited by anthony; 20-04-2020 at 07:39 AM.

  6. #5
    Join Date
    Apr 2019
    Posts
    471
    Post Thanks / Like

    Default

    If the bike only has 14k km on it then it's highly unlikely that there is a decompressor problem.

    I don't have a carb version F650 but I do have a CCM bike with large air cooled Rotax engine fitted with Mikuni carb (though not a CV version). My experience with the CCM is that the cold start device is only needed very briefly to start the engine but has to be backed off straightaway. It sounds as though your F650 is similar. Please note that the carb is not fitted with a choke as such but an enricher which is either on or off and, unlike a conventional choke, can't be gradually backed off.

    My CCM Rotax engine is not fitted with a decompressor and therefore the starter motor struggles to turn the motor over at any real speed. Despite that it always starts easily.

    You mention two spark plugs but, as far as I understand it, all pre-2004 F650 engines were only single spark and single plug? In order to check for a spark, just take our a single plug and with it still connected to its lead, earth the outside on a bare metal part of the engine or, alternatively, wrap a length of wire around the thread and earth the other end. Unless the spark produced is very weak and can only just be seen, it should be ok. You can compare the spark with the engine cold and engine hot to see if there is a significant difference.

    One of the issues with a large Rotax engine is that, especially when starting, it is very sensitive to the carb mixture especially if this is rich. If possible, I would check the colour of the plug after the engine has been allowed to idle for some minutes. If it is too rich, the spark plug will probably be very black with soot. The carb has a mixture screw to control idling and it might be necessary to check that is adjusted properly.
    2006 F650GS in Black
    9,300 Miles

  7. #6
    Bike
    F650 1997
    Join Date
    Apr 2020
    Location
    Bregenz, Austria
    Posts
    14
    Post Thanks / Like

    Default

    Quote Originally Posted by anthony View Post
    Vapour lock in petrol tank ? not letting fuel in carbs caused by engine heat or blocked tank vent .

    But re-reading your last post would say over-fueling as you do not need choke when cold.

    Do you turn off fuel tap ?

    Have you tried opening the throttle when warm starting ?

    You possibly need to check choke mech in carbs and float heights.

    Best to try this first turn of fuel tap and run the engine does the rpm pick up after a while if so could back up - wrong float heights or poor o ring around float valve seat.

    If it does this --- short term you could turn fuel tap off before you stop engine let it run for a minute to lower fuel height in carbs.

    Does not cost anything to try the last 2 above ideas. Let us know results.
    Thank you very much Anthony.

    - i do not suspect a fuel lock as the engine runs absolutely fine when warm, no variation whatsoever in idle speed, mixture seems to be good.
    - i always turn off the fuel tap when the bike is not in use. I always do this after switching off the bike.
    - The choke issue has been bugging me since I had the bike. With all my other carb bikes in the past choke was required when cold and would be used to hold the revs higher for a short time. This does not seem to be possible with the bmw. I cant seem to find a choke position which holds steady high revs enough to let go of the throttle. I am wondering if this could be a choke issue.
    - I have not tried applying throttle whhen starting for fear of flooding the thing.
    - When the engine is running and I turn off the fuel tap, the rpm should increase as the mixture will become leaner correct? So how would this indicate poor o-ring or float heights?

    On the next run I will try the following as you indicate and post my results:

    - turn fuel valve off while engine is running to check if the engine speed changes
    - turn fuel valve off and wait until the engine speed changes before switching off the bike.

  8. #7
    Bike
    F650 1997
    Join Date
    Apr 2020
    Location
    Bregenz, Austria
    Posts
    14
    Post Thanks / Like

    Default

    Quote Originally Posted by AWJDThumper View Post
    If the bike only has 14k km on it then it's highly unlikely that there is a decompressor problem.

    I don't have a carb version F650 but I do have a CCM bike with large air cooled Rotax engine fitted with Mikuni carb (though not a CV version). My experience with the CCM is that the cold start device is only needed very briefly to start the engine but has to be backed off straightaway. It sounds as though your F650 is similar. Please note that the carb is not fitted with a choke as such but an enricher which is either on or off and, unlike a conventional choke, can't be gradually backed off.

    My CCM Rotax engine is not fitted with a decompressor and therefore the starter motor struggles to turn the motor over at any real speed. Despite that it always starts easily.

    You mention two spark plugs but, as far as I understand it, all pre-2004 F650 engines were only single spark and single plug? In order to check for a spark, just take our a single plug and with it still connected to its lead, earth the outside on a bare metal part of the engine or, alternatively, wrap a length of wire around the thread and earth the other end. Unless the spark produced is very weak and can only just be seen, it should be ok. You can compare the spark with the engine cold and engine hot to see if there is a significant difference.

    One of the issues with a large Rotax engine is that, especially when starting, it is very sensitive to the carb mixture especially if this is rich. If possible, I would check the colour of the plug after the engine has been allowed to idle for some minutes. If it is too rich, the spark plug will probably be very black with soot. The carb has a mixture screw to control idling and it might be necessary to check that is adjusted properly.
    Thank you for the feedback. The bike is a 1997 model which has two plugs. i will remove the plugs today and see how they look.

  9. #8
    Join Date
    Apr 2019
    Posts
    471
    Post Thanks / Like

    Default

    I can now see it was designed for twin plugs! It is slightly surprising that they went to single plug for the early F650GS's (2000+) before changing back to twin plugs in 2004

    Let us know how you get on with the plug tests.
    2006 F650GS in Black
    9,300 Miles

  10. #9
    Bike
    F650 1997
    Join Date
    Apr 2020
    Location
    Bregenz, Austria
    Posts
    14
    Post Thanks / Like

    Default

    Quote Originally Posted by AWJDThumper View Post

    You mention two spark plugs but, as far as I understand it, all pre-2004 F650 engines were only single spark and single plug? In order to check for a spark, just take our a single plug and with it still connected to its lead, earth the outside on a bare metal part of the engine or, alternatively, wrap a length of wire around the thread and earth the other end. Unless the spark produced is very weak and can only just be seen, it should be ok. You can compare the spark with the engine cold and engine hot to see if there is a significant difference.

    One of the issues with a large Rotax engine is that, especially when starting, it is very sensitive to the carb mixture especially if this is rich. If possible, I would check the colour of the plug after the engine has been allowed to idle for some minutes. If it is too rich, the spark plug will probably be very black with soot. The carb has a mixture screw to control idling and it might be necessary to check that is adjusted properly.
    When checking the idle mixture by the colour of the plugs, i assume the engine must be hot? How long should i let the bike idle vefore switching off and removing the plugs?

  11. #10
    Bike
    GS/Gd Dakar 2003
    Join Date
    Oct 2008
    Location
    wakefield
    Posts
    1,633
    Post Thanks / Like

    Default

    Quote Originally Posted by Englischdude View Post
    Thank you very much Anthony.

    - i do not suspect a fuel lock as the engine runs absolutely fine when warm, no variation whatsoever in idle speed, mixture seems to be good.
    - i always turn off the fuel tap when the bike is not in use. I always do this after switching off the bike.
    - The choke issue has been bugging me since I had the bike. With all my other carb bikes in the past choke was required when cold and would be used to hold the revs higher for a short time. This does not seem to be possible with the bmw. I cant seem to find a choke position which holds steady high revs enough to let go of the throttle. I am wondering if this could be a choke issue.
    - I have not tried applying throttle whhen starting for fear of flooding the thing.
    - When the engine is running and I turn off the fuel tap, the rpm should increase as the mixture will become leaner correct? So how would this indicate poor o-ring or float heights?

    On the next run I will try the following as you indicate and post my results:

    - turn fuel valve off while engine is running to check if the engine speed changes
    - turn fuel valve off and wait until the engine speed changes before switching off the bike.
    my initial thoughts are fuelling or ignition
    Decompression lever issue was on Chinese made/assembled singles, manufacturing/wear issue with decompression lever. Compression drop when hot Unlikely with KM 13000 mileage on yours , unless valve clearance minimal , closing further when hot, even at KM 20-25k rarely need reshimming .

    float levels/needles, choke mechanism- been mentioned, sounds like rich mixture to start ok with no or minimal choke, may need adjusting, see FAQ's for full info ,
    you say; " I know that the carbs were completely stripped down and professionally cleaned before I got the bike,"
    I am wary of verbal or service history , would not be first time in my experience of cars & bikes what was said to have done hasn't . maybe worth a check float levels, crud in bowls, main jets, needle jets blocked or worn? If runs / starts better after fuel tap closed bit of a pointer.
    Coil issue or plug lead corrosion Issues common with this model, especially when hot. Whilst you have a new battery (check terminals tight, vibrations loosens them, can cause this issue ) , suggest voltage check static & running, VR major issue with this model, causes all sorts of symptoms, should get about 13.6v max running, may exceed this briefly on start up. Again see FAQ's for detailed info.


    2003 GS Dakar
    BMW Panniers, top box, tank bag
    + loads TT stuff that came with it!


Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •