Idles fine, but bogs with throttle.

Discussion in '2-Stroke Engines' started by Molotov256, Jul 31, 2009.

  1. Molotov256

    Molotov256 Member

    This engine is nothing but trouble, I swear.

    A while back I had this same problem - riding the bike just fine, came to a stop light, and when I tried to pull away and give it some gas, it bogged down and barely sputtered along. I pedaled it home, pulled off the carb manifold, exhaust, and head, applied a healthy dose of RTV gasket sealant on each gasket, bolted it back together, and voila, it worked.

    Anyhow, I've got maybe 40 miles on it since then, and I'm back to square one with the same problem. It looks like fuel may have been leaking out the front side of the head gasket, so I've got one ordered from SBP, but am I going to keep running in to the same problem? What else can I do? My other motor didn't misbehave like this.

  2. Hawaii_Ed

    Hawaii_Ed Member

    Did you also do the base gasket? The bottom of the jug has to seal to the block as well. Also check your fuel flow, and make sure the plug is clean.
  3. Molotov256

    Molotov256 Member

    I got the head gasket from SPB, but it doesn't fit. I asked them about this, and this was their response:

    "We only sell head gaskets for the 67-69cc "80cc" and 49cc engines. We also sell both 6mm and 8mm studs sizes in the 67-69cc size. It sounds like you do have a 59-60cc engine and we don't make one for that size engine. You could send the one you got back and we could replace it with the one for the 49cc but you would have to enlarge the main hole to fit your engine."

    I don't really have the means to accurately enlarge the hole in the 49cc gasket, so can anybody recommend another retailer who sells a gasket for my 59-60cc engine?

    Thanks for the response, Hawaii - the fuel flow seems to be okay, the plug looks fine as well, and I don't see any evidence of leaking sludge at the base of the jug. If there's no visual evidence, is it safe to assume the bottom jug gasket is sealing properly?
  4. arceeguy

    arceeguy Active Member

    If the engine idles fine, it pretty much eliminates the possibility of an "air leak". The slightest air leak would upset idle mixture and cause stalling or high idle speed that cannot be adjusted with the throttle stop screw.

    I'd look at some simple stuff first, like the spark plug - which might fire OK at idle, but misfires under throttle?

    Check the main jet in the carburetor. Maybe it loosened up - which would allow the engine to idle normally, but would severely enrich the mixture as you opened the throttle - leading to a lack of power.

    Make sure the exhaust port is clear from carbon deposits (although it takes a lot of running time for them to build up at the exhaust port), and make sure the muffler is clear. (could it be clogged with bits of RTV?) Run it open exhaust for a little bit to confirm.

    DJEEPER Member

    Maybe your float is stuck or needs to be adjusted? Sounds like you run out of fuel...
  6. Molotov256

    Molotov256 Member

    Stuck float?

    I just read a thread about somebody with a similar issue - you may be on to something with the stuck float. I will look during tomorrow times.
  7. moped-dan

    moped-dan Guest

    If it idles fine but it bogs down with throttle, your high speed gas jet is probably clogged. Clean your carb and spray carb cleaner in all small passages, make sure air can flow through all ports no matter how small. Put it back together and it should run great.

    By the way, since it idles fine I doubt you have a gasket problem, sounds definitly like a carb problem to me.
  8. jsttylr

    jsttylr New Member

    I'm kind of starting to have the same problem last two days but as of now i'm attributing it to humidity?
  9. Molotov256

    Molotov256 Member

    I think I may have found the problem. The float in my carb was filling up with fuel, so it wasn't floating properly. Reference the post below:

    I failed to mention the fact that gas was leaking from my air filter as well, but that's happened so many times on this engine I didn't think it was a noteworthy occurrence. As it turns out, it probably is. My hopeful diagnosis is as follows:

    1) Gas leaking from air filter
    2) Engine idles okay, but bogs with throttle

    1) Float is either stuck or saturated with fuel. Replace.

    I'ma order a new float ASAP and see how it pans out.
  10. Molotov256

    Molotov256 Member

    Wait... who sells floats?

    Wow - I switched carbs between the working bike and the wrecked one, and it's night and day. It would appear that the semi-sunk float was totally bogging down the carb. All I need now is a new float... or I may just buy an upgraded carb from spooky tooth:

    I could have sworn I'd seen a website that sells floats around somewhere. Who sells 2 cycle NT carb floats?
    Last edited: Aug 2, 2009
  11. arceeguy

    arceeguy Active Member

    That would have been a dead giveaway!

    Glad you found it. You're probably better off buying a complete carburetor. Check out eBay, they are cheap.
  12. wagonrd

    wagonrd Guest


    For what it's worth from wagonrd: I have spent 6 weeks working on a motorized bicycle, using the GT80 66cc 4.5 HP engine. I'm out hundreds of dollars and the machine is still non functional. The problem now is a bogging engine. I've gone thru the checklist. The problem, folks, is that I, and many of you, have been snookered by the clever Chinese bike engine makers, aided by the bike motor dealers here in the USA. It's junk, spelled with a capital J. I should have known better, for I flew the A6A Intruder in Vietnam, and that machine was a horrendous piece of junk, with 90% of the systems failing on the cat shot and what was working failed on the arrested landing. The answer is straightforward: Use a bicycle for the purpose for which it was built....pedaling. If you want a motorized 2 wheeler, buy a motorcycle. Trump is right, the clever Chinese have outsmarted we dumb shits.
  13. crassius

    crassius Well-Known Member

    I've been a full time repair shop for these for quite a long time - even though some are worse than others, you get much more than your money's worth out of them if you take the time to do them right.
  14. Wolfshoes

    Wolfshoes Member

    In the recent posts about the engine bogging down, the type of carburetor is not mentioned. Using the Grubee stock CNS carb I have seen this problem and traced it to not always having the rubber boot where the throttle cable enters the carb properly in place. I could speculate that without the boot in place the carb runs too lean when the throttle is turned and the engine stops firing. The CNS carb also stops firing when riding up a steep incline, also assumed to be running to lean. Overall, it is not a bad carb but under some situations, including riding into the wind, it does not runs as smoothly through the power band as another bike I have with a Gasbike provided stock NT carb. If the carb does not have a boot; use black tape or something similar over the connection from the throttle cable to the carb and give it a test. The difference could be huge.