Weak-Sauce Acceleration

Discussion in 'Motorized Bicycle General Discussion' started by mkingsley, Mar 31, 2011.

  1. mkingsley

    mkingsley New Member

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    So I've had my first build for a couple of weeks now. Great bike and all was running well until a couple of days ago.

    Every time I am riding at around 35 miles an hour and I slow down to about 10, accelerating back up seems to be a problem. I can't just gas it up full throttle like I used to, I have to slowly accelerate to get back up to speed or for a more speedy alternative I have to choke up my bike. But we all know how much of a hassel that can be.

    I'm wondering if anyone has had a similar problem in the past and knows any fixes to this problem? My throttle cable seem to be operational so that leads me to believe it could be something in my carburetor? Any feedback is much appreciated.
     
  2. Nougat

    Nougat New Member

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    When you go to accelerate, does the engine rev, but not seem to be catching? If so, you need to adjust your clutch so it grabs better. The couple weeks of riding have worn the pucks down just enough where they're not grabbing anymore. (You are pedaling from a stop before letting the clutch out, right?)

    If the engine isn't revving under throttle so much, but once it gets up to top end it runs fine, this is where you'd adjust the clip setting on the jet needle. Ride with the bike at a little over half throttle for a couple minutes, then shut it off and check your plug right away. The plug color will tell you whether you're lean or rich, and you can adjust your needle clip accordingly (up is a little leaner, down is a little richer).

    If it's not even getting up to top speed anymore, I would be looking at an air leak. Carb to intake, intake to cylinder, possible carb top, make sure your head is torqued down, possible headgasket or cylinder base gasket leak, possible crank seal leak.
     
  3. mkingsley

    mkingsley New Member

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    Yeah, before I let my clutch out I've got momentum. But as you just said I think I may have a leak. I didn't mention that now when I'm riding I'm getting about 7 mph lower than my top speed was previously. Another few strange things about my set up is that my bike fails to idle. I've been adjusting the pin to try and find that sweet spot and no luck.

    Is it true that if I completely remove the idle pin while the engine is running it should die? If so, mine doesn't die. I thought that once the pin was removed the engine sucks up so much air that it shuts down. Any input on what could be causing that?
     
  4. Nougat

    Nougat New Member

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    Other way around. When there's an air leak, the idle tends to soar. The idle screw being out will create a small air leak, but not enough to make a super big difference. Look for an air leak and go from there.
     
  5. mkingsley

    mkingsley New Member

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    Cool beans. Thanks for the prompt responces. I'll be sure to respond to this thread once I've figured out the problem
     
  6. 2door

    2door Moderator
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    Definitely sounds like an air leak to me. Double check where the carburetor attaches to the intake manifold and the manifold to the cylinder. This is the most common area for air leaks. There are others but let's start with the simple stuff first.
    Tom
     
  7. that guy on a bike

    that guy on a bike New Member

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    good luck im working on the same problem with no luck. im told the main jet is too big for the carb. my bike ran great for a week. so frustrated
     
  8. bairdco

    bairdco a guy who makes cool bikes

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    if your bike ran great for a week, and then started having the same problem as mkingsley's, there's no way the main jet could be too big for the carb, unless you've changed it.

    it's not like your bike works great one moment, then thinks, "y'know? i don't like this jet. i'm gonna stop working good.."

    look for an airleak, if it's the same problem. you might wanna check the fuel flow, too. make sure it's not clogged up with rust or dirt anywhere.
     
  9. Nougat

    Nougat New Member

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    That guy: my response about carb tuning in the other thread was not to your problem specifically, but in frustration over hearing "just move the needle clip" one too many times.

    I apologize for any confusion that may have caused. Indeed, if your bike ran great, then started being weird, an air leak is highly probable.
     
  10. "the prussian" Shop Dogs

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    You realy have to check everywere to find leaks. Take the covers off and look for fuel res. I just had a leak from the stator mount hole.
    http://db.tt/i8q5OoC <-- pic link
    That was a bear to figure out at first, but it's very satisfing to fix stuff yourself.
    Did you change fuel mix at all ? Or like bairdco say's run thru whole
    fuel system.
     
  11. that guy on a bike

    that guy on a bike New Member

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    o.k. I sealed everything i could. took the intake spacer out sealed it back in then sealed all the gaps around the clamp. Then i made a gasket for the cable piece tightened that back on. Port matched the intake and the exaust. Took it for a spin and was doing a little better. Started right up, then after it warmed a little i was running it without the choke. Was'nt getting full trottle but slowly on flat i could gain speed. the after 5 five minutes of doing o.k. it started boging and a noticed gas flowing out the overflow. Runs with the fuel valve off untill it starves itself. flowing gas won't stop with it turned on. As fast as its flowing theres now problem with gas getting in the carb.
     
  12. Nougat

    Nougat New Member

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    Either a piece of crud is holding the needle valve open, or your float is leaking, and no longer floating high enough in the bowl to close the needle valve.

    Take the float bowl off to inspect. Shake the float to see if there's gas in it. If there is, replace. If not, clean the needle valve out.

    I'd bet it's a bad float.
     
  13. skiball83

    skiball83 New Member

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    Im thinking you have a CNS carb. Red air box. Get rid of it and buy a NT from thatsdax.com for $11 + sh. When you get it adjust the needle to the second from highest notch and try it out. OR...your muffler might be clogged. Happened to me. Take it off and blow through it. If its hard to blow through then drill it out with a 1/4" bit. Good luck...it sucks now but when you get the hang of the china girl you will love it and she will love you, maybe for a long time. Pun maybe intended. LOL. PS check your gas cap. It might not be venting. When it starts running ruff take off the cap and put it back on. If it runs better for a couple minutes, well there is your problem.
     
    #13 skiball83, Apr 2, 2011
    Last edited: Apr 2, 2011
  14. that guy on a bike

    that guy on a bike New Member

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    ya its the stupid red air box carb. It said high performance so i looked passed the air box.
    I think I might have to listen to you Skiball and get another carb. All i hear are good things about the NT. The cns that came with my kit ran great at first utill i broke the intake clamp. All my smarts (and j b weld ) could not get the thing to run right again. I bought a new one (without finding this fourm first)exspecting the same performance but it has been none stop problems from the start. My wife told me to get the cheaper one but I told her this one was better. She was probly right again. Don't want to spend anymore on it right now, so i'm gonna mess around a little more. I can't let this little carb defeat me yet. I'll take all the advise i can get though.
     
  15. "the prussian" Shop Dogs

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    I had a float were the little tabs that alow float to hinge were screwed up , had same result of nonstop flow . Just a little tweak with needlenose fixed her right up.
     
  16. that guy on a bike

    that guy on a bike New Member

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    Gonna go mess with the float now. can anyone show me what a NT carb looks like?
     
  17. Black_Moons

    Black_Moons New Member

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    Hmm. Well, Not sure about your flooding problem, But try doing a run with the gas cap loose/removed, And see if the WOT/acceleration problem persists. That will tell you if your gas cap needs a vent drilled (most do if they have not been.. AFAIK stock ones are not vented properly and sometimes seal enough to stop flow into the engine after a few mins of running, And the 'seal' can occure a few weeks after puting gas in the tank (Rubber gasket expands/gets wet enough to seal?)

    Choke will often get the bike running again during fuel starvation till it gets too bad.
     

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