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83 Maxim Suddenly Won't Start

Discussion in 'The Garage' started by Hasty, Jul 28, 2022.

  1. Hasty

    Hasty 1983 Maxim XS400

    19
    8
    3
    Ottawa
    After some great advice on here, I had solved my problem with leaking "gas" and got my bike idling the best it ever has. BUT then I tried to take it around the block, it died halfway and now it won't start. Looking for ideas on what I can check to try and track down my new issue. Relevant info:

    - When I hit the starter, it cranks and sounds like I'm getting combustion, but won't catch and start.
    - Compression is in spec (142 psi on the left, 148 on the right)
    - Valve clearances are all in spec
    - Carbs have been disassembled and cleaned several times while tracking down my last issue and once after this new issue started. They've got brand new diaphragms and float needles. Idle circuit appears clean when I blast cleaner/air through it
    - Battery and spark plugs are both brand new and I have spark on both sides (attached a spare plug to the boot, touched that to the plug in the engine, saw spark across the gap)
    - Idle mix screws are 3-1/2 turns out from seated

    Before now, I had never had any problem at all getting it to fire up (all my problems came once it was running). What's the next thing I should be checking to get it to start again?
     
  2. Jared salsano

    Jared salsano XS400 Member

    If I was getting spark and had good compression, I would check to see if I was getting fuel. Could be something stupid like a stuck float.
     
    Hasty and CaptChrome like this.
  3. CaptChrome

    CaptChrome XS400 Addict

    I agree with what Jared said. First check for a fuel delivery issue to the carb. Verify you have flow from your petcock to the carbs then that you have the correct fuel level in the carb float bowls (use some clear 1/4" (6mm) tubing attached to the bowl drain and visually verify the level in the bowls.)
     
    Hasty and Jared salsano like this.
  4. Buddha

    Buddha XS400 Addict Top Contributor

    I would check if I ran out of fuel in the tank, been there done that!
     
    Hasty and Jared salsano like this.
  5. Hasty

    Hasty 1983 Maxim XS400

    19
    8
    3
    Ottawa
    lol @Buddha definitely a good one to double check! I did confirm that there's plenty of gas in the tank. Chrome and Jared, it's good you brought up the fuel levels because I'm actually not 100% sure I've been measuring them from the right place. The manual says 3 +-1 mm from the "mixing chamber body edge" so is that the split between the float bowl and the rest of the carb body (red line in the photo), or the bottom of the ridge where they fit together (blue line in the photo)?
     

    Attached Files:

    BambinoFan likes this.
  6. Hasty

    Hasty 1983 Maxim XS400

    19
    8
    3
    Ottawa
    Oh also I rebuilt the petcock a couple weeks ago so I can confirm it flows with vacuum on RES and ON and freely on PRI. I put an inline fuel filter on it too so I can see the gas moving through that
     
  7. Jared salsano

    Jared salsano XS400 Member

    That's a question for captainchrome, he seems to know a lot more about it than I do
     
    Hasty likes this.
  8. CaptChrome

    CaptChrome XS400 Addict

    I think it is the red line on your carb as it is the joint you see from the outside. I think your fuel level is too low (much better than being too high, so good on ya!).

    If it were me, I would set it 3mm below the red line and try it, but I would also monitor carefully to see if I get any of the symptoms of too high a level (fuel coming out of the air filter joint, rising oil level in the crankcase, smell of gas from the breather). You are on the right path, just be careful and try it. If this isn't it, you will know pretty quickly.
     
    Hasty likes this.
  9. BambinoFan

    BambinoFan XS400 Member

    Agree with capt. Definetly 3 below the red, as per the manual, at least.
     
    Hasty likes this.
  10. BambinoFan

    BambinoFan XS400 Member

    yeeeepppp. Thought I was SOL first time it happened to me. Thank goodness for res.
     
  11. Hasty

    Hasty 1983 Maxim XS400

    19
    8
    3
    Ottawa
    Awesome thanks, I was away over the weekend, but should have a chance tonight to try and raise that level a bit and see if it helps
     

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