Honda 'surging' at partial throttle

Discussion in '4-Stroke Engines' started by Sketch, Feb 8, 2010.

  1. Sketch

    Sketch Member

    Got my replacement engine (thanks Jeremy/birddog). Got it all put together and things went pretty smooth. I'm being very careful to run at partial throttle, especially for the first 100 or so miles, and I'm experiencing a surge that makes me nervous about a problem and also makes the ride less than enjoyable. I am being subtly pitched forward and backward as I go down the road. It is not smooth. It's unsettling.

    If I am at any partial throttle level, the net effect is that (like I already said), the power is surging - so 1 or 2 seconds of smooth power, followed by a fall-off in power, followed immediately by another 1,2 or 3 seconds of smooth power.

    I don't think the first engine did this.

    It's not the engager, it is definitely staying engaged. I have it permanently engaged and there is no disengagement going on.

    I'm thinking (based on reading threads here):

    oil sensor switch?
    the large amount of grease I packed in the gearbox this time, affecting the clutch?
    kill switch wiring, as Irish John mentioned in a thread?
    the engine not firing on a cycle(s), for reasons other than kill switch or oil sensor?
    fuel flow?

    Now, as another clue, keep in mind this is ONLY during partial throttle. I tried running wide open for a short stretch and the ride becomes smooth, no surging.

    Thanks in advance...

  2. arceeguy

    arceeguy Active Member

    Sounds like the engine is running lean, most likely due to a carb problem. A simple carb cleaning will probably fix the issue.

    Low oil sensor will shut the engine off, it will not produce surging. Same goes for kill switch issues, especially if the engine runs more consistently at WOT.
  3. ocscully

    ocscully Member

    You aren"t going to like to hear this, but it may be the Governor? The Governor when it works as designed not only limits max. rpm, it also causes the rpm's to increase when the engine becomes loaded.

  4. HoughMade

    HoughMade Guest

    I hate to say it also, but that was what I was thinking.
  5. Sketch

    Sketch Member

  6. Sketch

    Sketch Member

    I think there is a spray can of carb cleaner here. What is the easiest way to clean the carb? Do I have to take it all apart?
  7. Sketch

    Sketch Member

    Can I really rule out fuel flow? I mean, I haven't inspected the filters.
  8. arceeguy

    arceeguy Active Member

    Yep - just spraying cleaner down the throat of the carb will do nothing.

    You need to drop the fuel bowl, and force the cleaner in to every little orifice in the carb. The more you can dis-assemble and clean, the better.
  9. arceeguy

    arceeguy Active Member

    If the engine runs better at WOT than at partial throttle, you've ruled out the fuel filters.

    Partial throttle bogging is most likely due to a clogged circuit in the carburetor.
  10. ocscully

    ocscully Member

    No I'd go ahead and take the time to check out your filters just to be sure there is no problem. How does the motor idle? Does it run smooth and steady or does it surge? What I see/hear in your description sounds to me like the Governor doing its job.

    Last edited: Feb 8, 2010
  11. arceeguy

    arceeguy Active Member

    Hmmmmm - after re-reading this thread and picking up the fact that this is a brand new engine - the carb should not be in need of a cleaning.

    However, it does still exhibit signs of running lean at partial throttle. A properly running engine, even with governor, should not surge IMO. If the temperature is very cold, it could upset the fuel mixture as these engines are jetted lean for emissions reasons - and cold air will exacerbate the problem. Honda may offer different jetting to compensate for varying operating conditions. (low temperature, high altitude, etc.)
  12. Sketch

    Sketch Member

    I saw in several threads where people thought the treatment (can't remember what it was called) could cause a brand new engine to need it's carb cleaned. I can certainly remove the bowl and maybe dig a little deeper.

    I will also try what I saw recommended to check fuel flow - just get a jar (or in my case, nice stretch of gravel on a country road...) and disconnect the line and see what it looks like. The see-through filter certainly looks totally clean inside.

    And yes, I have confirmed with a couple more tests, at WOT there is no surge going on.

    Thanks for the help.
  13. Egor

    Egor Guest

    The carbs are poor. I had to fool around with every part of the thing to get mine to run. It is the dumb C.A.R.B laws they have them leaned out so much to meet the law it makes for a just barely running engine. I put a small piece of wire in the air bleed hole to fatten up the mid range, now it just about perfect. It needs the two small holes next to the butterfly in the runner enlarged. That would not be easy. Try running the choke part way on and see if it gets better, that is the indicator. Have fun, Dave
  14. ocscully

    ocscully Member


    Any update on what you found to be the problem or what you did that seemed to fix the problem?

  15. loquin

    loquin Active Member

    Which Honda are you talking about, BTW? I don't think the GX35 has a governer, but, the GXH50 does.
  16. Old Bob

    Old Bob Member

    No govenor on the GX35, in any case surging is not normal operation for a govenored engine, as mentioned before its a mixture problem.
  17. professor

    professor Active Member

    My 2 cents- I bet if you richen the main jet, the problem goes away. My HF was real lean - had to choke for a long time before it would take throttle. Opened the jet 3 thousandths and all is well.
  18. Danny3xd

    Danny3xd Member

    Not a suggestion but I am re-learning that a brand new engine always seem to have some sort of growing pains. Just a thought.

    If I remember correctly my new GX50 had a bogging problem that disappeared after a few hrs.
    Another thought/question, does she vibe hard at mid range?