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Help Any DRZ400 experts? FCR39 carb

Discussion in 'Maintenance' started by Linkin, May 20, 2020.

  1. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    Have a DRZ400E in the shop, low km's, been sitting, not able to get it to stay running. Backfires through the inlet and stalls. Unable to get idle speed set properly, either too high or too low.

    Owner has had it elsewhere and weren't able to get it running at all

    As its a slide carb the idle adjuster changes the point at which the slide stops, further adjusting done with mixture screw to get correct idle speed.

    Carb has been stripped, cleaned, and had a carb kit put through it. New everything.
    45 pilot, 65 starter, 160 main jet, all standard. All air jets have been replaced, along with all o-rings and seals (except mid body seal). Played with float height as well. Had it in and out so many times we will have to replace the manifold and clamps before it goes out, I can pull the carb out with my eyes closed now.

    Valve timing and clearances are good, decomp as well

    Air filter is good

    No air leaks

    New battery

    Charging system good

    New spark plug

    Symptoms:

    Struggles to start without choke, either idles low and then stalls or backfires through the inlet, or idles too high. If the throttle is blipped it rises cleanly, very responsive, and will either hang or drop to a low idle, then start popping out the exhaust followed by a backfire and/or stall.

    Spark plug is a CR8E and has been replaced, checked it again and it was black and sooty but not wet.

    Adjusting the idle stopper or mixture screw I can get it better but not perfect, can't seem to find a happy medium, have tried 45 pilot (std) and 48 as well. Service manual doesn't list a specification for how high the slide should be at idle, only idle speed of 1800rpm and mixture screw setting of 1.5 turns (won't idle or stay running). Have gone either way to 3+ turns and back in below standard setting with no success.

    The bike gets very hot very quickly.

    Mixture screw has been changed to one that can be reached with the carb in the bike, it was an absolute pig to reach before but now can be done easily.

    The carb is absolutely 100% clean through all passageways and jets, it's spotless.

    The fuel squirter is set and working properly


    This isn't my first DRZ with an FCR39 but I just cannot get this one to stop backfiring and stallling!

    Wondering if I need to start looking at the main jet or needle clip position now.
     
  2. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Have you tried starting it with someone's hand over the intake side of the carby to seal it off ?
    Sometime's it can help to clear passage's inside the carby that were blocked up.
    The palm of your hand will get wet with fuel, and the bike will be harder to start for the first few kick's, but if it fire's up and run's a bit better then you know it's still a problem in the pilot circuit.



    Had a quick look online and people have suggested mixture screw be set at 2.5 turn's out, and the slide sitting low
    A split Coast Enricher hose can also cause similar issue's
    Can be bypassed for testing etc, check the rubber cap on the cylinder if it has been bypassed as they can perish/split
    And if they're bypassed they usually need the pilot circuit adjusted to stop backfiring on decell

    [​IMG]
     
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  3. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    The bike is standard apart from the snorkel on top of the airbox which has been removed.

    I'm aware of the coasting enrichener. I have pulled the cap off and checked the diaphragm/spring and replaced the o-ring, and double checked that I haven't fitted anything backwards.

    I will probably try blocking off the enrichener and seeing if it makes a difference.
     
  4. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    'except mid body seal' that would be the first place I would look, just sayin :)
     
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  5. Murdo

    Murdo The Good Doctor Staff Member Contributing Member Ride and Events Crew

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    Coil is crap?
     
  6. kiffsta

    kiffsta Senior Member

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    Sorry, I am bored

    coil.jpg
     
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    Last edited: May 20, 2020
  7. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    Hahaha :D
     
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  8. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    Good advice!

    Today I pulled the mid body apart and what do you know, the pilot passgeway was full of crumbled o-ring.

    I tried to preach the benefits of litetek seals to my boss :thumb_ups: Maybe in the future I will be able to convert him to the green side.
     
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  9. risky

    risky risky

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    well is it running properly?
     
  10. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    We are waiting on the new mid body seals to arrive before I can put it back together and test, but based on the contents of the mid body and condition of the seals, its safe to say it was the cause of the poor running
     
  11. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    We only do mid-body seals for the downdraft carbs. Everyone else is doing them too now. Including several customers that copied them and sell on eBay. It happens.
     
  12. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    Ok so the mid body kit arrives today, I set to work and got the carb reassembled with stock jetting and mixture and it instantly came to life and idled. Set the idle speed at 1800rpm per the manual, checked throttle response, perfect.

    Here's a selection of what the old bits looked like. Idle/mixture passageway was totally blocked with crumbled o ring.

    4AE7B7ED-93FA-4CFC-8B0C-E256971DCC92.jpeg 029F76FA-D9E0-4A76-BB5B-274F62764528.jpeg D4E75B89-6CAD-462B-9D31-6E33688C9C78.jpeg 8F43A437-8E1D-47F4-9B15-C171CFC7BE2B.jpeg
     
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  13. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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  14. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    Both, two screws on the exterior, two inside the float bowl that hold on another piece (slide housing?), and the outer edges are epoxied, very hard stuff.

    I used a heat gun and leverage to break the epoxy seal.
     

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