Zama carb adjustment

Discussion in 'Mechanic and Repair' started by Grassmangrass, Jun 14, 2011.

  1. Grassmangrass

    Grassmangrass LawnSite Member
    Posts: 18

    I have a couple of new Echo SRM-225s with the Zama carb. Also, a Zama carb on a Echo PB-251 blower. I do not see any High or Low adjustments on these carbs. I am told they are there, but I cannot seem to locate them. In case I would need to make adjusments, I would like to know. The manuals only state how to adjust idle, and say to take to dealer for other adjusments.

    Any knowledge is appreciated.
    chris
     
  2. Merkava_4

    Merkava_4 LawnSite Bronze Member
    Posts: 1,280

    Is your carburetor the Zama RB-K93 ? . . . Echo is indicating that it is.

    On the RB series, the adjustable idle needle is inside the rotor at the top of the carburetor. There's a tamper resistant
    plug covering the idle needle directly above it. Zama shows the idle needle represented as (O) in the drawing:

    [​IMG]

    [​IMG]
     
  3. Grassmangrass

    Grassmangrass LawnSite Member
    Posts: 18

    Merkava_4,

    Thanks for reply and the diagram. I am assuming then the only adjustment to this type of carb is to remove the tamper resistant plug and then adjust the idle needle for the fuel adjustment for either high or low. Does this require a special tool?

    I am trying to compare this to the older carbs that had the H and L screw adjustments.
     
  4. Merkava_4

    Merkava_4 LawnSite Bronze Member
    Posts: 1,280

    You know, I'm calling it an "idle needle," but Zama refers to it as a "throttle valve needle." That needle might control the mixture for the whole RPM range; I'm not a 100% sure on that though. What I do know from studying these service manuals is that the needle travels up and down inside that main nozzle as you move the throttle. By the looks of it on the drawing, I'm assuming all you need is a small straight-slot screwdriver to turn that needle.
     
  5. Grassmangrass

    Grassmangrass LawnSite Member
    Posts: 18


    Thanks Merkava_4
     
  6. Mikesmowing1

    Mikesmowing1 LawnSite Member
    Posts: 2

    Hello,

    I was wondering if anyone knew how to get the "tamper resistant
    plug covering the idle needle" off? So far it has resisted all of my efforts to tamper with it, but I would really like to get in and adjust the carb a little better.

    Thank you
     
  7. herler

    herler LawnSite Fanatic
    Posts: 5,144

    I can predict the future, someone trying to adjust mixture needles is going to be ordering up a brand new carburetor after they've fiddled with it so long they can't remember the stock settings, because you're not going to get it to run "better" or as some folks think, faster or stronger.
    The only thing that adjusting mixture needles can do for you is to enrich or lean out the mix, neither of those is going to give your engine more power because the amount of air entering the manifold is determined by the size of the carburetor and so long that stays the same, you get the same performance.
    The only thing that changes is whether it's running rich, lean, or just right.

    Read: Opening the main jet to deliver more fuel will NOT make it run harder, stronger, faster, or better.

    Let me tell you how we do it...
    We pull the plug to see if it's running rich, lean, or just right.
    You need a chart handy so you can tell from the looks of the plug!
    And based on that we might give the main jet a 1/4 turn (in for leaner, out for richer).
    Then run it some hours, and pull the plug again.

    The process for adjusting the idle jet is separate.
    Some folks refer to the main jet as the High and the idle jet as the Low, we call it main and idle.

    That's how you adjust a small engine carburetor but again you're not going to get more power, not unless your mix is a long ways off.
     
    Last edited: May 30, 2012
  8. herler

    herler LawnSite Fanatic
    Posts: 5,144

  9. piston slapper

    piston slapper LawnSite Platinum Member
    Posts: 4,240

    Herler......you making this stuff up as you go?????
    If you can predict the future....you knew this was coming.....
    Posted via Mobile Device
     
  10. Mikesmowing1

    Mikesmowing1 LawnSite Member
    Posts: 2

    Actually... The carb is putting out to much fuel and I would like to decrease the fuel. The engine runs as if it is constantly choked, but it's not. Also, after it has ran for some time, the air filter is sopping wet with fuel.

    So... anyone know how to get the tamper resistant plug out?

    Thank you for the spark plug chart, I will be using that at work tomorrow, it's great!
     

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