Drz400 runs great, won't idle: Help

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

  1. Allanrps

    Allanrps Adventurer

    Joined:
    Apr 3, 2014
    Oddometer:
    99
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    Rolling in the Deep
    Just got an 07 drz400sm. Previous owner said it worked but had been sitting a few months with a blown head gasket.

    After replacing the gasket and cleaning the carb repeatedly, bike still won't idle.

    Starting cold, fully choked, it starts up and sounds pretty nice. Then switching to half choke, it will sit around 2800rpm. Ive test ridden it, and it does great. Fine through the rev range, but with or without choke, if I try to get it to sit anywhere below 2800rpms, it dies.

    Once it gets warmed up I hear an occasional skip, rpms varying a couple hundred in either direction.

    Played around w throttle screw, set fuel mix screw to stock 2.5 and played with that too.

    It's been like this since the first time I put the carb in, and since then I've completely disassembled it and gone through it w carb cleaner, and pine sol soaked multiple times. Also cleared with compressed air twice, all circuits.

    Stock carb, airbox, jets, and exhaust.

    At a loss, any help would be very much appreciated. This bike's supposed to be my daily driver.

    Thanks
    #1
  2. Allanrps

    Allanrps Adventurer

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    I'm sure the pilot jet is clear, passage from pilot jet to idle mix screw is clear, the three holes under the throttle plate are clear, the passage from the air box side to the pilot jet are clear, and all the accelerator pump(?) passages are clear.

    Are there any other passages associated with the idle circuit I'm missing? As far as I'm aware everything in there regardless of circuit is clear, but just in case.

    Checked orings, needle seal, and float height. Every time carb goes back in it's the same.

    Backed fuel mix screw all the way out and it doesn't help the idle. I start to hear little puffs which would indicate to me the bike is running rich. When I close the fuel mix screw, the bike dies. Anything between 2 to 4 turns doesn't provide any noticeable result.

    By using the throttle stop screw I can get it to idle around 1800 unchoked, but the moment I rev up, it takes off and doesn't come back down.

    Checked for air leaks with starter fluid all around the carb and the cylinder head as well.
    #2
  3. Dirtmonkey8

    Dirtmonkey8 VA is for Riders

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    I don't think they came with pumper carbs stock. Maybe the previous owner never got it dialed in well and now it is still a bit dirty in there and acting up? maybe try something simple like taking the cover off the airbox to give it more air and see what changes? Maybe research which jets should be in it for your elevation and replace them all with new. Folks drill out jets or gouge them with wire and this could be tripping you up. I think all new purchases for me will be fuel injected bikes. Good luck.
    #3
  4. Beezer

    Beezer Long timer Supporter

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    does it still have a vacuum petcock? if not, is the vacuum line plugged off? if yes, maybe it leaks. there should never be fuel in that line
    #4
  5. SantaFeTrailer

    SantaFeTrailer social distancing since before it was cool

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    It usually takes me more than one try to get carbs clean. :dunno
    #5
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  6. MotoChris521

    MotoChris521 motominded

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    I bought a used DRZ400. It took a while to figure out the PO had drilled out the stock pilot jet twice the size of the stock one.
    I'd start there.
    #6
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  7. Dno

    Dno Been here awhile

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    I remove the pilot to clean and visually inspect. Really the only way. To small of a hole not to. I use the high E guitar string(.009 in) to clear jet. Lately Ive done it with a bread twist tie with coating burned off in desperation of not finding my " tool". Then a modified baskeyball needle in a nozzle and a rubber tip nozzle can verify all passages with compressed air.
    #7
  8. ptgarcia

    ptgarcia Make America Great Again!

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    I highly recommend replacing the pilot jet. They just don’t clean up well, and who knows what the previous owner did to it. Your symptoms are common and point to a fouled pilot jet. Also, be sure to not swap the main for the pilot when reinstalling. It’s an oftentimes made mistake when cleaning the BSR carb.
    #8
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  9. sandwash

    sandwash Long timer

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    Pilot jets are cheap, just change it out.
    #9
  10. AZ TOM

    AZ TOM Long timer Supporter

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    Increase main jet.
    #10
  11. SoManyFish

    SoManyFish Been here awhile

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    It could be a carb issue. Other inmates have made some great suggestions for dealing with those. However, because the head gasket was blown and then replaced, the issue could also be that you still have a head gasket leak. That is replacing the gasket does not rule out the possibility that the head gasket is still leaking. When you replaced the gasket, did you check the flatness of the head? It could be warped out-of-spec. Was all visible gasket residue removed before installing a new gasket? Was the torque sequence followed properly? Have you run a compression test after replacing the head gasket? Leaking head gaskets often don't leak until the is warmed up (because metals expand as the heat up) so, if possible, run the compression test while the engine is warm.
    #11
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  12. Tree_weaver

    Tree_weaver Adventurer

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    Mine has done that several times. In my case, it was always the pilot jet. One time I cleaned the jet, but wasn't good enough. Put in a new pilot, ran perfect again.
    #12
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  13. Lowrider49

    Lowrider49 Adventurer

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    I've had an 05 E and an 07 SM since new. I usually rode my TW 200 or the 400E and let the SM sit...bad idea. Sold the E and TW and was left with the SM which wouldn't run worth a shit. I played with the carb for 6 months ...mostly cold weather and not riding. Couldn't get it to run right. Finally I put in a Honda ATV 650 clone carb and a low restriction air filter and it runs like a new bike and lifts the front wheel off the road in 2nd. I'm not suggesting it as the only fix but it sure made it into a lot faster and reliable bike.

    Gotta agree...only FI bike from now on. Just bought a 2021 NC750DCT and it is a super bike, not as fast as my 1250 Bandit but fuel injected and super smooth automatic. I still have the old 2003 Lowrider but it's never been a problem with a carb. FI RULES!!
    #13
  14. PNWet

    PNWet Long timer

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    I have not had a deep dive into my DRZ carb.

    However, in my XR250R I found the air cutoff valve (a rubberized canvas disc) that is common in Keihin carbs was completely eroded/shot due to ethanol fuel. I had struggled with multie cleanings, jet replacements, etc. Once I replaced this little ethanol damaged rubberized disc, it has run perfectly since.

    Ethanol dissolves rubber and clogs jets and small passages.

    Looking at the DRZ diagram, it looks like there are a couple of diaphragms. Part 41 in the Suzuki schematic, labeled diaphragm assembly, part #1348010F00, appears to be the DRZ equivalent of my XR air cutoff valve.
    #14
  15. LashLarue

    LashLarue Been here awhile

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    Just had a similar idle problem. Also had a bike that leaked gas on the floor almost immediately after turning off. Fix for me was a new needle valve in the carb. Think I changed the thing the needle valve slides into also. No more leaks, great idle, and better mpg. Note, the same bike had a new needle valve in 2018 so it doesn't take long to fail.

    2004 DRZ400e
    #15
  16. cycleman2

    cycleman2 Long timer

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    Does this bike have the stock Mikuni carb? When you had the carb apart did you notice if it had different jets and a non stock needle. I would just get an aftermarket stock carb overhaul kit and start over. If the bike is stock put it back to stock. At least then you have a starting point. An idle that won't come down or hangs up and is slow to go back down usually indicates a lean condition.
    #16
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  17. Toe

    Toe Grab your gear

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    Worth checking out the community jetting spreadsheet as a "just in case".

    As others have collectively said make sure the jets are actually clean (pilot caught me out too) and not modified, all the lines are crack free, float settings, etc for usual carb things
    #17
  18. Nortonbrian

    Nortonbrian nortonbrian Supporter

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    fishing line to clean jets, kinder than wire.
    #18
  19. Dno

    Dno Been here awhile

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    You can charge the fishing line with compound. Draw the line tight with jet on it. Then spin the jet as pulling it back and forth. The jet gets lapped. Used the fishing many times. Was going to put the above in originally. Just got get fishing line through. Guitar string usually gets the hole open so I can get the fishing line through.
    #19
  20. cycleman2

    cycleman2 Long timer

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    Just remember the jets are made out of brass, which is very soft and easily messed up when cleaning with anything other than carb cleaner and compressed air.
    #20