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Thread: Z400 problem

  1. #1
    Join Date
    Dec 2012
    Location
    Quebec
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    47

    Z400 problem

    A month ago while riding my '05 z400 hard, I stopped to refuel and then I wasnt able to start it. Finally bump started it but it ran like crap and stopped again like 2minutes after. I wasnt able to start it, neither by pushing it. Got back home ,cleaned the all the ground on the frame, changed the plug, cleaned my air filter, changed the oil and it ran fine for 2hours in the sand pit. then while coming home by the road it started to run like crap but it didnt stall. I opened the carb, inspected the jets and everythings , and the carb is as clean as a clean carb can be. Went for a trail ride, it ran for 5 minutes and stopped while slowing down to cross a road. Was able to bump start it once, ran like crap and stopped, exactly like the last time. Then it never started again. Came back home, plug was super white meaning it runs lean but usually my plug is a clean brown. Tried running another coil, didn't work, drained the tank and dropped new gas, didnt work. the petcock flow like new. It has sparks. Switch is good. Inspected all the wiring harness.I dont have a compression gauge, but the piston is only 2 years old and if the compression was super low I wouldn't be able to start it. Yesterday I've been able to ride it for 30 minutes before it stalled. It never takes the same time before it stalls. I always clean my airfilter after every ride and I change my oil every 15hours ( suzuki recommends every 6months) . I noticed yesterday that it was losing prestone. I refilled the rad and it got empty again. I've found no leak. Before it stalls, it always starts to backfire.

    So, could my engine stall because it is burning prestone?
    could it be a bad cdi? electrical wise, it is the last piece I have not tested ( because we can't)
    Or any idea? I'm lost on this one

    ( english is not my main language, so if you dont understand something, tell me and I'll do my best to explain it)

  2. #2
    Join Date
    Aug 2014
    Location
    South Louisiana
    --
    1,915
    If your plug is white then you may need to rejet. Sound like lean conditions and running hot are causing coolant to be burned quickly. Running hot could be frying the stator. Is it smoking? Is the coolant in the oil?
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  3. #3
    Join Date
    Dec 2012
    Location
    Quebec
    --
    47
    Found no coolant in the oil and the quad is jetted correctly because before i got this problem my plug was a clean brown. I've been running it jetted this way since one year and it always ran good. Can a spark plug become white because of pre-ignition? Or could she be white because the quad is simply running hot because of a cooling problem, like a bad waterpump? By the way I love your 125 build!

  4. #4
    Join Date
    May 2013
    Location
    Henderson, Tx.
    --
    974
    If I am not mistaken, those early Z400s had a problem with the water pump. I think it was a chemical reaction between the aluminum, magnesium and coolant. Don't recall if it was an internal or external leak. I'd research that if I were you. If I'm wrong someone will correct me.

  5. #5
    Join Date
    Feb 2011
    Location
    Surprise, AZ
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    2,430
    I am guessing it is a blown head gasket on the piston side only, which is why you are losing coolant and why it is "washing" the plug white, plus coolant doesn't burn very well and will cause starting issues a water pump would cause it to run hot and it would boil over out the vent hose and at some point it would change the plug color, but that does not explain the starting issue when the engine is cold.
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  6. #6
    Join Date
    Jul 2009
    Location
    South Florida
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    6,722
    The z400 are known for blowing head gaskets / warped heads and constant valve shimming .
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  7. #7
    Join Date
    Dec 2012
    Location
    Quebec
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    47
    It starts well when it's cold. I will tore the top-end appart and look for a bad gasket. Is prestone always flowing through the top-end or does it only flow when the engine needs it? And would burning coolant explain why I'm not able to start it after it stopped?Thanks guys
    Last edited by j013N; 01-04-2016 at 08:59 PM.

  8. #8
    Join Date
    May 2013
    Location
    Henderson, Tx.
    --
    974
    Quote Originally Posted by j013N View Post
    It starts well when it's cold. I will tore the top-end appart and look for a bad gasket. Is prestone always flowing through the top-end or does it only flow when the engine needs it? And would burning coolant explain why I'm not able to start it after it stopped?Thanks guys

    Yes, coolant is always in the cooling passages. It only flows when the engine is running, because the pump is turning. Many engines with weak head gaskets will start fine when cold. Mostly because the cooling system is not under pressure, and therefore coolant isn't being forced into the cylinder. There may be some coolant in the cylinder already, but, not enough that it struggles to start (any coolant that may have been in the cylinder usually finds it way into the crankcase). Once the engine reaches operating temperature the coolant has gotten hot and expanded, creating a pressurized system. Shut the engine off and that pressurized coolant forces it's way into the cylinder through the weak spot in the head gasket. Enough coolant gets in that it cannot be burned. An engine with a completely failed head gasket will hydro-lock because one or more cylinders are nearly completely filled with coolant, and can't turn over. Ever see a crankcase filled with "milkshake"??

    Another thing that often happens with a weak head gasket, and subsequent low coolant level, is that engine compression is forced into the cooling system. When that happens coolant can/will be forced out of the system via the radiator cap, or next weakest area. Also, heat from the engine's compression, that is being forced into the cooling system, raises the coolant temp, and forces it to evaporate. It also creates air bubbles, which form air pockets, in the cooling system and air in the cooling system just doesn't work.

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