Zama C1Q Check Valve Replacement with Pics

Discussion in 'Mechanic and Repair' started by Maico490, Aug 21, 2010.

  1. Maico490

    Maico490 LawnSite Member
    Messages: 5

    Hi everyone. I'm a newbie here and have only posted once on a thread on a primer bulb going dry on a Stihl trimmer. Searching throws up the fact that a lot of people have symptoms which point towards check valve problems. The general reply is "Get a new Carb" which is the case if the check valve is not working on the idle circuit. However the main check valve is fairly easily replaced for $4. This is copied over from a post i made on a chainsaw site:

    This has been my first experience with the notorious check valves found on newer carbs. I've been chasing this problem on a FS450 trimmer for a while but luckily it has been between cuts on Water Authority sites. Searching here didn't throw up much but these carbs are used on lots of blowers, trimmers and smaller saws. The carb is a Zama C1Q-S34H which is fixed jet with only what appears to be an air screw (reverse thread) for idle adjustment.Symptoms were hard starting, inconsistant idle which couldn't be adjusted and would run out of fuel with an inch still left in the tank. When operating the primer bulb you could keep pumping without it becoming full and air bubbles were visible in the bulb. At full throttle everything was fine but as soon as you let off it would often stop dead. New lines, primer bulb,fuel filter and a rebuild kit did nothing. The answer was eventually found on Zama's excellent website:
    Before you do anything to a Zama carb I would recommend reading all the Service Tips. Especially DO NOT BLOW COMPRESSED AIR THROUGH A CARB WITH CHECK VALVES. It seems you also have to be careful with aerosol carb cleaner if directed straight into the valve with an extension tube.


    The jet at the bottom of the metering chamber is the main jet which Zama call the "Nozzle Assembly Check Valve". Stihl call it the "Valve Jet".
    The hole in the middle, which is normally hidden by the metering lever leads to the idle circuit. To test both circuits use a piece of hose over the jet and blow with your mouth. If clear then try to suck back. If you can the check valve is defective. In general if it is working you can hear a faint click. If you can suck back it is bad news on the idle circuit as it means a new carb but the main jet can be replaced. Zama do a special tool but I managed to use a cheap drill press and one of my extensive collection of broken drill bits. This is clamped in the chuck upside down. If you have adjusting screws remove the H before starting.


    It took a fair bit of fiddling to get everthing lined up and more force than I expected to get the nozzle to move. It pushes straight through into the bore of the carb. The chuck is stationary throughout. Here it is out and the new one:


    The new nozzle pushed in quite easily with a bit of oil on it to the same level as the old one.
    A few minutes of reassembly and it fired right up. Ticks over fine now and is responsive to the LA screw.

    Zama C1Q-S34H 001 [800x600].JPG

    Zama C1Q-S34H 002 [800x600].JPG

    Zama C1Q-S34H 003 [800x600].JPG
  2. Merkava_4

    Merkava_4 LawnSite Bronze Member
    Messages: 1,443

    Excellent thread!! Thank you for taking the time to post all this info. :)
  3. BigFish

    BigFish LawnSite Platinum Member
    Messages: 4,194

    I agree, great job!!
  4. jtsnipe

    jtsnipe LawnSite Member
    Messages: 199

    Thanks for the info.Being a amateur small engine mechanic it's nice to have one more option in my repertoire.
  5. dboyd351

    dboyd351 LawnSite Bronze Member
    Messages: 1,126

    Excellent step by step post.
  6. jkilov

    jkilov LawnSite Bronze Member
    from MS
    Messages: 1,415

    A main nozzle check valve prevents air from entering the carb on idle. When faulty the unit idles poorly and dies on acceleration.

    There are two main types: mechanical (like this one) and capillary screen.

    Note: only butterfly carbs need check valves, another reason why I prefer barrel carbs.
  7. ricky86

    ricky86 LawnSite Silver Member
    Messages: 2,142

    The check valves, idle and main, prevent air from entering the metering chamber when using the primer. Any carb with a primer has check valves. They serve no other purpose.
  8. dboyd351

    dboyd351 LawnSite Bronze Member
    Messages: 1,126

    Would it then follow that if you are getting air in the primer bulb when attempting to prime the engine, despite the fuel filter being immersed completely in fuel, that the check valve has gone bad? Any way to know which check valve? I see Maico490 describing putting a piece of hose over the check valve and alternatively blowing and sucking, but I'm not clear on how you get that piece of hose to seal over the check valve.
  9. jkilov

    jkilov LawnSite Bronze Member
    from MS
    Messages: 1,415

    Partially true, but I'm 99% sure the main nozzle check valve in a butterfly carb is crucial for a stable idle.

    Either way a faulty main valve will allow the purge bulb to suck air through the nozzle rather than fuel from the tank.

    And yes you can check a mechanical main valve with a piece of hose. Not so with a screen valve, these really can't go wrong other than plugging up which would cause other problems.

    Of course you could stop fiddling and get a new carb :laugh:.
  10. ed2hess

    ed2hess LawnSite Fanatic
    Messages: 14,588

    Zamba is the only Echo used carb that I can't figure out.....often a tear down and cleaning and new kit doesn't do much of anything. I got three of them in the shop now and debating whether to buy the $11 kits.

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