Drz400 runs great, won't idle: Help

Discussion in 'Thumpers' started by Allanrps, Jul 1, 2021.

  1. PNWet

    PNWet Long timer

    Joined:
    Nov 2, 2014
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    1,528
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    Puget Sound, WA, USA
    Well? It's been almost a month...
    #21
  2. Dno

    Dno Been here awhile

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    I agree. The white electrolysis scale is tough for chemical removal. Swore Id make a vapor blaster. When there is water in the air lines the compressed air works better.
    #22
  3. cwadej

    cwadej Keeper of the truth

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    #23
  4. Aesc

    Aesc ... just dawdlin' along ...

    Joined:
    Mar 20, 2008
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    Location:
    Queanbeyan, New South Wales
    In prepping for a 6500 km (4000 mile) outback trip, my '17 DRZ400E started up and ran fine - on choke initially, then off choke - except at idle. It just wouldn't. So, after initially trying a tank full of fuel additive, which didn't work, took it around to a local Suzuki bike shop. He removed the Mikuni FCR39 carby and cleaned it up in an ultrasonic bath. Some improvement but very erratic idle. So, in the end stripped the carby down and replaced internals with a carby kit from Mikuni. Problem solved. Bike ran fine on the outback trip and since. No further issues to date. Shop feller said quite a common issue with these, especially if being lefty sitting for too long.
    #24
  5. AbnormalWrench

    AbnormalWrench Adventurer

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    Jul 14, 2021
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    seattle
    I used to work as a motorcycle tech for several years, and you spend what feels like half your time cleaning carbs...or at least, you did back when I worked on bikes. That being said, many people have mentioned the idle jet needs to be cleaned, but in my experience, that is only half the job. I personally preferred using a throttle cable, cut off the end and then unwind the cable a bit, the individual strands are very fine. You aren't trying to ream the jet, all you are doing is unclogging it, like a snake in a sink. Squirt it with carb cleaner and blow it out with compressed air. Hold the jet up to your eye and look at a bright light, you should easily see light through the very small opening in the jet. Repeat as necessary. Make sure the emulsion holes are clear on the side of the jet also.

    But the thing that most people miss is the transition ports. The air/fuel mixture mixes in the idle jet and has two outlets. One is the idle mixture screw, which bypasses the throttle plate. The transition ports are two to three holes that are just below the throttle plate. They supply fuel as the throttle plate is opened, and if they are not working correctly, it will idle badly and choke up when you try to give it gas. Those ports are what people miss the most when cleaning carbs. They are very small and can be stubborn. I do not poke anything in them, with the mixture screw in place, idle jet out, carefully spray carb cleaner using a straw into the place where the idle jet goes and it may take a bit of manipulating of the straw, but with the throttle plate held open so you can see what is going on, you should find a sweet spot so you get a solid stream of carb cleaner out of ALL the transition ports. It doesn't usually take much work, but if you have doubts, hit it with carb clean, then it hit it with compressed air, then hit it with carb clean. Repeat until you can get a solid stream of carb clean out of each transition port.

    One other thing I have seen people mess up, don't over torque the mixture screw when seating it. You want to be very very gentle when bottoming it out. Then you back it off. I recommend 2 turns as a starting point. If you know you already bottomed it out with some force, that very well may be your problem. It damages the seat and there's nothing you can do about it but replace the carb. But then the previous owner might have done that....something to keep in mind.

    Hope that helps.
    #25
    LexLeroy, spokester and Dno like this.
  6. Dno

    Dno Been here awhile

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    Dont forget pumper, enrichment circuits, and vent. Best to verify as mentioned above.
    #26
  7. SoManyFish

    SoManyFish Been here awhile

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    Apr 18, 2017
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    Canada
    Hey Allenrps, did you ever resolve this issue? If so, could you please let us know what the cause and fix were? Thanks
    #27
  8. FluffyDog1969

    FluffyDog1969 Adventurer

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    Feb 21, 2020
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    Erie, PA
    He took it for a test ride into the dessert.... never to be heard from again....
    #28
    pdmigs likes this.
  9. Arguenaut

    Arguenaut Adventurer

    Joined:
    Oct 24, 2016
    Oddometer:
    15
    Vacuum leak
    #29