She Just Ain't Climbing Like She Used To - Standard China Girl Motor 66cc

Discussion in 'Motorized Bicycle General Discussion' started by Russ McClay, Jun 11, 2013.

  1. Russ McClay

    Russ McClay New Member

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    66cc standard China Girl HT (haha) motor
    Mountain bike frame

    Everything stock except:
    Sick Bike Parts air filter
    Sick Bike Parts fuel valve
    Inline fuel filter
    NGK BP6HS spark plug


    I built my fine bike in January of this year (2013). After working out the usual bugs one will likely encounter, she has been running great! Over 1000 miles on the odometer (about a 1/3 of those coasting-no-engine miles).

    After a 60-mile run around the north end of the island (Taiwan), I started noticing she wasn't pulling the same steep parts of hills I ride ALL the time. Had to pedal more. A lot more on very steep sections. We're talking up to 30% slope (grade)! For comparison the steepest grade on the US Interstate Highway System is only 8%.

    Here's some data from the little video cam I use showing the elevations:

    [​IMG]

    This has stumped me because the bike starts very easily. It sounds great. It still runs at the original top speed on medium grades. Doesn't leak any oil. Chocolate plug. Idles fine, even after chugging up a big ol' hill and suddenly disengaging the clutch! Doesn't smoke. By nearly all accounts this is perfectly broken-in power plant running on a 32:1 oil/fuel ratio. Head torqued down properly. No air leaks. Vented gas cap. Fuel flows freely to the carb. No four-stroking. I weight 130 lbs.

    Why have I lost a bit of low end torque?

    Even after installing a brand new plug and a spare new NT carb today, the performance on the hills I know so well was considerably less than a month ago consistent with recent results. It runs OK, no problem, on the lesser grades.

    But later today I decided to remove the nut on the muffler cap and pull the innards out. Seems there are many variations. My cap has one hole for the fastener bolt and one 7 inch or so tube that extends from the exhaust hole. Whatever else is inside is welded into the casing...so I can't really see it. The inside is carbonized dust...not oily. Looks good.

    So for a quick 300 yard test uphill, I left the cap off and fired it up. Had to immediately back off the idle screw on the carb, but then it was running fine. And it had this really nice snappy sound to it. Obvious a bit louder with the cap off.

    Then I took off up the hill. Wow...definitely a true increase in performance. But I've read here from old-timers...that it's not good to run without the muffler cap...2 strokers need back pressure. That's true. But it seems like there's some baffles still in the muffler which are still providing some back pressure.

    In any case...I plan to buy a SBP's expansion chamber, even though it will cost $60 bucks to ship to Taiwan! (And it's probably made across the pond from me in China.) I know it will give me all the power I need to climb based on today's experiment.

    In the meantime does any one have an ideas about what is causing a loss of power? The original performance was perfectly acceptable to me. I don't mind pedaling a bit up those steep bits. But now pedaling much more than before.

    [​IMG]


    brnot
    Happy motoring!
    Russ
     
    #1 Russ McClay, Jun 11, 2013
    Last edited: Jun 11, 2013
  2. oldtimer54

    oldtimer54 Member

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    Re: She Just Ain't Climbing Like She Used To - Standard China Girl 66cc

    Sounds like your muffler might be getting clogged? Or the problem is that its a HT engine?
     
  3. Russ McClay

    Russ McClay New Member

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    Re: She Just Ain't Climbing Like She Used To - Standard China Girl 66cc

    The biggest change I've been able to achieve is pulling the cap off the muffler. So yes...maybe it's clogged or not open enough.

    I don't quite get "is the problem is that its "an" HT engine?" Is that a joke? =)

    And, oh yeah...I'm an old timer '55.

    Cheers,
    Russ
     
  4. oldtimer54

    oldtimer54 Member

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    Re: She Just Ain't Climbing Like She Used To - Standard China Girl 66cc

    HT engines are know for not lasting. No pun intended.
     
  5. Russ McClay

    Russ McClay New Member

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    Re: She Just Ain't Climbing Like She Used To - Standard China Girl 66cc

    Hey oldtimer --

    What is it that is not lasting? Overall all quality? What mysterious element of these simple engines has caused my motor to lose a bit of its shine?

    Compression? Ignition? Brand new carb today, so that's out.

    I've seen the most abused Chinese-made 2-stroke weed-whackers operate with impunity to abuse for years here. lol One would expect the same type of factories that churn those out also turn out China Girls.

    Do you have any hard evidence that HT engines are known not to last? What does "last" mean? 1000 miles?

    I ask in humor but with true curiosity as to numbers and facts.

    Cheers,
    Russ
     
  6. Toadmund

    Toadmund New Member

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    Re: She Just Ain't Climbing Like She Used To - Standard China Girl 66cc

    Well, mine didn't last, my crank pin bearings shredded and ground up my piston and cylinder.
    What I first started noticing was loss of power and top speed and towards the end it wouldn't stay idling and was harder to start.
    This happens because the scoring on the piston and cylinder causes loss of compression and as the bearing gets shredded, it gets worse.

    If I was you Russ, I would park it and pull off the head and see if there is a problem there.
     
  7. crassius

    crassius Well-Known Member

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    Re: She Just Ain't Climbing Like She Used To - Standard China Girl 66cc

    there is a small catalytic converter on these welded to the inlet pipe about 2 inches down from the top (just below the upper weld on the outside cover)

    this has a fine mesh that can coke up

    now that they are welded rather than bolted together it isn't really worth the effort to try to drill up into that area

    you could, however try drilling SMALL holes in the lower cap to see if you can relieve some pressure without getting too noisy - try one hole then two and so on
     
  8. dodge dude94

    dodge dude94 New Member

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    Re: She Just Ain't Climbing Like She Used To - Standard China Girl 66cc

    At 1000mi at 32:1 oil/gas ratio, I'd be willing to bet the muffler is clogged. However, your clutch is nice and sticky, right? No slippage?
     
  9. mapbike

    mapbike Active Member

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    Re: She Just Ain't Climbing Like She Used To - Standard China Girl 66cc

    Russ, first off I would like to say that some of the HT/China Girl engines last a long time and some dont I have an older 2009 engine that has 1600+ miles on it and still runs like a champ, no mods accept a well tuned carb and a free flowing exhaust.
    This bike cruises at 30mph all day long without a glitch.

    Russ, I think you have already answered you own question here, you removed the end cap of the exhaust and you got your low end torque back for pulling those hills, seem the obvious problem is that over time you have developed some flow restriction in the exhaust, I would take a long steel rod and by hitting it with a hammer I would punch several larger paths through the honey comb looking stuff you will see up inside your exhaust muffler and then put the end cap back on and give it a try.

    NOTE: remove the exhaust before doing the mod to open it up more through the catalytic part that has a honey comb look to it, the stock exhaust are to restrictive for these engines from my experience and freeing them up using the method I described is a bit crude but it works and will allow the engine to breath better.
    I did this very thing on one of mine one time and it allowed the exhaust to start flowing better and it made a noticeable difference on the hills, be sure and clean the spark plug really good and use a wire brush to knock the soot off of it and then after a nice run do a plug check to make sure the aded air flow hasn't caused a lean run condition.

    if you are using a really high quality oil you may even consider going with a 40:1 mix and see what that does as well, sounds to me like you just have some simple tuning issues from a plugged up exhaust that need to be done and then you'll likely be good to go again and maybe even better than before.

    Best wishes and I hope you get it back to good on the hills asap.
    Map
     
    #9 mapbike, Jun 13, 2013
    Last edited: Jun 13, 2013
  10. Russ McClay

    Russ McClay New Member

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    Re: She Just Ain't Climbing Like She Used To - Standard China Girl 66cc

    Hey Map --

    Thank you for the reply!

    Today I got to really test my theory at lunch. I rode up to Yang Ming Shan National Park on the steep back road without the cap. The little bike had more power than when it was first broken in. It screams! All the places where I had to pedal (when the speed dropped to about 15 mph) I cruised at 18 to 19 mph. This is a huge difference! It's loud, but in the mountains it doesn't matter. Actually it sounds awesome. Also. The top end is still there.

    I bought my kit directly from a factory in China which shipped it here to Taiwan. The muffler doesn't have any of the EPA honeycombs. Here's the end cap:

    [​IMG]

    Inside I see a larger diameter tube (1/2 inch maybe), that's capped. That is inserted through a very thin metal disk which is the size diameter as the inside of the muffler. There is a gap all around it between it and the muffler inside. There is also a hole in it for the cap tube to fit into.

    The large tube and disk and screw rod are all welded into the muffler.

    My thinking now is just to unscrew the fastener nut and pull the cap when I need to climb and throw the cap in my tool bag. Then when I'm on the flats and in the city, I'll just let the muffler cool off a few minutes and put it back in. All this until I get a real expansion chamber.

    I've also thought about cutting off the pipe that is connected to the cap and bending that disk. But am reluctant to do that, or drill holes...

    As for the oil, I've already backed off a bit. Going with about 36:1 for starters.

    I would like to say that all motors are different, so I don't suggest any running without the cap.

    Motor safe!
    Russ
     
  11. dodge dude94

    dodge dude94 New Member

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    Re: She Just Ain't Climbing Like She Used To - Standard China Girl 66cc

    The caps like that are the ones that most people saw off the tube, then drill out the exhaust tip to increase flow.
     
  12. biknut

    biknut Active Member

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    Re: She Just Ain't Climbing Like She Used To - Standard China Girl 66cc

    Has the weather changed since you first got it running? Have you done any jetting, or are you running the stock jet? Have you changed the oil ratio over time? Just fyi as you change your oil ratio, you need to change your jetting to compensate.

    Less oil = richer

    Stock jetting is usually on the rich side.

    Since it sounds like your motor is in good shape, if all else fails try an expansion chamber. The one from SBP works well.
     
  13. fatdaddy

    fatdaddy New Member

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    Re: She Just Ain't Climbing Like She Used To - Standard China Girl 66cc

    HT or "Happy Time", Is simply a "fit all" term to describe all the chinese 2 stroke bicycle engines. Thatsdax or BGF, It's still a HT engine. I believe it's derived from one of the first sellers of these engines from China, a company that called itself Happy Time. The engine itself is an old Russian design that the Chinese copied and mass marketed to the U.S.
    fatdaddy.
    And yeah, check yer exhaust. You can do this by simple removing the baffle, (cap,) from the end of your pipe. (and riding it.)
     
    #13 fatdaddy, Jun 13, 2013
    Last edited: Jun 13, 2013
  14. neum5464

    neum5464 New Member

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    Re: She Just Ain't Climbing Like She Used To - Standard China Girl 66cc

    http://www.ebay.com/itm/NEW-47cc-49...804?pt=LH_DefaultDomain_0&hash=item5d2e1c3be4

    might take some welding but take the head pipe from the old kit, cut and attach to this pipe because 2-stroke motors generally like to have expansion chambers to create the proper back pressure for the motor to be most efficient. the stock exhaust pipe works better on the 4-stroke engine kits.
     
  15. mapbike

    mapbike Active Member

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    Re: She Just Ain't Climbing Like She Used To - Standard China Girl 66cc

    Russ, glad to hear you got the bike running better, be sure to do a plug check while running with exhaust opened up. I would cut that tube off and grind it down even with inside of cap and make sure the engine is tuned good for that set up and just run that way if it is.
    Best wishes with your bike, hope it gives you great service for a long time.
    Peace, Map
     
  16. Russ McClay

    Russ McClay New Member

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    Re: She Just Ain't Climbing Like She Used To - Standard China Girl 66cc

    Hey dodge dude --

    Good to hear. I'm thinking I'll do that. Also I can bend back a disk baffle which is just a single piece of thin metal that has a hole in which the tube from the cap goes into.
     
  17. Russ McClay

    Russ McClay New Member

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    Re: She Just Ain't Climbing Like She Used To - Standard China Girl 66cc

    Hey biknut --

    The weather has changed...more humidity and higher temperatures. No jetting. Stock jet. Oil ratio has been scientifically measured...32:1 for the last 600 miles. I recently dropped the oil mix to 36:1. But that was after I noticed the loss of power.

    Yeah, I am definitely going to go for the SBP pipe! Due to shipping I'll have to pay as much for it as I did the whole motor kit! Not SBP's problem. And I should plug them further. I bought their fuel valve, air cleaner and a couple of other things and they were shipped promptly to Taiwan. I had one simple tech question. They answered right away. SBP is sick! lol

    Cheers for the feedback!
    Russ
     
  18. Russ McClay

    Russ McClay New Member

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    Re: She Just Ain't Climbing Like She Used To - Standard China Girl 66cc

    Today I fully confirmed the power loss is due to the exhaust system. It was really the last thing on my list of things to focus on. Let's face it, these engines are simple...there's only so many things that can be wrong with regard to poor performance.

    At lunch I took a ride on a hill that I know very well. Even with the motor at its best I would have to pedal up a few very short sections which was acceptable. With the cap off I flew up that hill and did not have to pedal anywhere along it! And hitting the top I immediately disengaged the clutch to see if it would stall. But no, it just keep idling fine. It's obviously too frickin' loud...but I would almost say the motor seems to like it...and the loud sound sounds GOOD! It's snappy like a high octane dirt bike.

    Then I went up the most outrageous set of switchbacks I know of near by. I've only tried it once before and was pedaling almost all the way when the motor was at its most powerful. The mountain is named Zhong Zheng Mountain, Zhong Zheng is the affectionate name for Chiang Kai Shek.

    There used to be two huge Chinese characters carved into the forested mountain face which is so steep the characters almost appeared to be vertical. The men who used to maintain it, old Kuo Ming Tang soldiers stopped doing so about 7 years ago and since then it is now completely overgrown and filled in with trees. This road I rode goes there.

    I powered up that all the way, only pedaling briefly on one or two of the switchback curves and that's only because you have to slow down to take them on; they're hairpin curves. I am amazed! That's pretty much the baddest ass hill I'd ever have to climb in north Taiwan.

    * * *

    I think I will retain the power gains of a removed muffler cap by cutting off the stinger tube (as suggested above) and trying to drill out the existing exit port.

    I'm so stoked to find out why my bike wasn't climbing like it used to. I thought: "Oh well these are cheap little engines and they only last so long." But you should of heard that little girl powering up those tight switchbacks through the woods and mountains! It was yee-ha!

    I'm going to run her a few more times up the hills over the weekend, weather permitting, and then check the plug as Map wisely suggested. I don't like pulling NGK plugs because the soft aluminum washer/seal is designed to be tightened down once for a good seal. Fortunately I have a brand new spare plug.

    I'll do a sound recording with my GPS/Video cam on the next ride.

    brnot
    Motor safe,
    Russ
     
  19. oldtimer54

    oldtimer54 Member

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    Re: She Just Ain't Climbing Like She Used To - Standard China Girl 66cc

    Sound like your having fun. Good. Your going to love the SBP pipe I have one and it rocks.
     
  20. Russ McClay

    Russ McClay New Member

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    Re: She Just Ain't Climbing Like She Used To - Standard China Girl 66cc

    OK...here's a video from today...working that Girl hard on the hills with no muffler cap.

    http://youtu.be/8aYwNR1q134

    brnot
    Motor safe,
    Russ
     
    #20 Russ McClay, Jun 15, 2013
    Last edited: Jun 15, 2013

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