engine "hunting"; what causes this?

Discussion in 'Mechanic and Repair' started by rbig, Oct 17, 2005.

  1. rbig

    rbig LawnSite Member
    Messages: 112

    My engine has started "hunting" (surging) lately. It does this at low throttle settings. It is slight, but there. Once the throttle is advanced, it runs strong and smooth.

    What should I look for to fix it?
  2. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

    Well, I can only guess not knowing what it is !!!! If it has a low speed adjustment screw open it up a little, If it's a fixed jet carb. then it needs to be taken apart and cleaned and possibly a rebuild kit installed. The problem is the carb. is running a little lean and doing the above task should smooth it back out.
  3. stumper1620

    stumper1620 LawnSite Bronze Member
    Messages: 1,889

    1 bad spark plug could cause this too. I've seen 1 plug do it on briggs a few times before, otherwise yes, RPM hunting is normally a lean fuel mix, pull the choke on a little and see if it smooths out, if it does, check your fuel filter first if its ok then you need to do what Rob said.
    I had to replace the carb on my Honda 24 Hp because of this. never did find the cause but, the new carb fixed the problem.
  4. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

    Not trying to be a smart azz or anything I just want to explain how I came to my diagnoses. First, I did inadvertently forget the plug because thats the first thing I check or replace. I eliminated a clogged fuel filter because it requires more fuel to operate higher speeds than lower and the unit in question runs fine on higher speed. Although applying the choke slowly will confirm a problem in the low speed circuit it is not required. If the unit in question had a surge at higher speed then it would require applying the choke slowly to determine if it is a problem in the high speed circuit of the carb. or a governor problem. If the choke is applied and the surge goes away that would indicate a carb. problem, If the surge continues that would indicate a out of adjustment or faulty governor.
    While typing this one other detail came to mind, If the engine in question has a small spring on the throttle linkage rod and is broken or disconnected this also could cause a low speed surge. Honda and Kawasaki are critical to having this properly connected.

    Stumper, As for having to replace the carb. on your Honda, I've ran across 3 or 4 the last couple years that nothing I did would make them perform properly and never found out why just ended up replacing them.

    Take Care All
  5. VegetiveSteam

    VegetiveSteam LawnSite Senior Member
    Messages: 296

    How old is the engine? The regulations on emissions these days can sometimes cause a hunt at low speeds. These engines are running much leaner then they did even a few years ago. I have customers tell me that engines they've had in the past never hunted and now this new one does. Well the engines of the past didn't have all this government interference either. You used to not have to flush your toilet more than once too but the government stepped in and gave us low-flow toilets so now we flush twice sometimes. Same thing here. The government steps in and says these engines are polluting the air so they have to run leaner. Leaner means hunting. Not all engines do it but if you get the right stack up of minimum tolerences you can very well have it.
    If it's only at low speeds and a very minor hunt I wouldn't do anything as long as it's running good and strong at full throttle when you have it cutting. If it is a fairly new unit with low hours it may go away after you get a little more time on it.
  6. stumper1620

    stumper1620 LawnSite Bronze Member
    Messages: 1,889

    I was not questioning you in the least Rob,
    I know you are far more qualified in this area than I am. just thought I would point out the plug failure since I had seen that a few time before.
    I really am glad to hear that about the carb on my Honda though, that sucker got tore apart 4 times before I finally gave up and ordered another.
    $180 bucks on a 2 year old low hour motor did not make me a very happy camper.
    that motor is on my stump grinder and it had a long period last year that it sat. wierd thing with stumps, thats a spring and fall machine, Very little call for stumps in the summer months.
  7. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

    I done the same thing with the ones I replaced also so got tired of monkeying around with them. On your stump grinder do you put stabilizer in the fuel when you park it for long periods of time ? It also wouldn't be a bad idea to start it up once a month and let it run for 15 to 20 minutes if you don't already do it.
    Take care

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