walbro wt-38 carb: primer bulb required?

Discussion in 'Mechanic and Repair' started by jcliburn, Mar 15, 2008.

  1. jcliburn

    jcliburn LawnSite Member
    Messages: 3

    Hi folks. I bought a walbro wt-38b carburetor to replace the zama c1q-s63a carb that came stock on the stihl fs-85 I bought 7 or 8 years ago. (The machine over the past couple of years has gotten progressively worse starting and running. This year it finally became untenable, and basically wouldn't yield to *any* carburetor adjustments I made. Fuel also began leaking from the carb itself.)

    The walbro carb doesn't have a primer bulb on it; the zama does. Since the walbro didn't come with a bulb, is it intended to operate without one? Would it hurt anything to add one?

    One reason I ask is because the fs-85 fuel tank has two fuel line ports drilled into it: one for the main fuel feed line to pass through, and another for the primer bulb vent line to pass through (I guess that's what it's called). If I don't use a primer bulb on the walbro carb, I have to plug one of those tank ports, since, in the absence of a primer bulb, there's no place to hook up the vent line that passes through it. If I add a primer bulb to the walbro, then I have a place to hook up the line.

    Any guidance appreciated.
  2. BigShelby

    BigShelby LawnSite Member
    Messages: 13

    Without a bulb, how do you plan to get it started when the engine is cold? Everything I own Stihl, Husq, Echo etc. all have primer bulbs. Would a retro fit of a bulb be an option on your new carb?
  3. jcliburn

    jcliburn LawnSite Member
    Messages: 3

    I mounted the new carb yesterday and started the unit without trouble. <shrug>

    As for the retrofit, yes, I can use the bulb from the zama if the walbro actually needs one. You've hit at the core of my issue, though: Does the walbro *need* a bulb (since it didn't come with one), and will it cause problems if I add one?

    Thanks for the reply.
  4. kayeproperties

    kayeproperties LawnSite Member
    Messages: 141

    I never use primer bulbs unless I run the machine out of gas. It seems to be easy to start eithe choke it for a pull or 2 till it hits and then its all go. I use Echo, shindawa and huscavarna mostly but I have stihl as a backup. On my stihl the primer is a whole seperate unit so you might want to go with that arerangement. Good luck. What do you think went wrong with the other carb? Dirty plugged wore out?
  5. jcliburn

    jcliburn LawnSite Member
    Messages: 3

    Just for closure, I plan to operate the walbro carb without a bulb; the zama bulb mounting screws didn't fit the walbro body, so I can't reuse it.

    It took me about 10 pulls to start the machine this morning after running it dry yesterday. If I leave gas in the carb, the machine starts on the second or third pull when the engine isn't warm. That's good enough for me. It runs a *heck* of a lot better with the new carb.

    kayproperties, I don't know what went wrong with the old carb. It was leaking fuel and I could no longer find a set of adjustments that were satisfactory through the operating range. I could've probably installed a kit and made it all better, but I got impatient. Meh... 46 bucks for a new carb (including shipping) after about 8 years of good service from the machine seemed like a fair compromise against the time it would've taken me to rebuild the carb.

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