Newbie questions for upgrading

Discussion in 'Motorized Bicycle General Discussion' started by UTmotorbiker, Oct 12, 2014.

  1. UTmotorbiker

    UTmotorbiker New Member

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    Ok sooo I don't really know where the appropriate place is for these questions but here goes:

    I have a few questions about my new PK80 motorized bike. First it's a brand new motor so my first question is how many miles do I need to ride it to consider it "broken in?"

    Second, I attached a bike speedometer to my bike and my average speed is between 20-25 mph (mostly around 20) and I'd like to get a cruising speed of averaging around 30 mph. I have purchased a 41T rear sproket and I'm guessing I'll get some more speed from that. Currently my top speed (with a 44T) has been 30 and thats going downhill at a pretty decent slope. I'd really like to get close to that speed on the flats. Any ideas for simple upgrades to get it up around those speeds would be great.

    How fast should I expect to go with the motor broken in and a 41T sproket?

    Thanks!!

    .trk
     
  2. Greg58

    Greg58 Well-Known Member

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    Welcome to the forum, somewhere around 250 to 300 miles is where these engines start to perform their best. The general rule is to run about 3 tanks of 24/1 mix then go to 32/1 with good oil, good synthetic oils that are low smoke run real well. My 48cc engines will do 30 on flat ground so yours should get better as time goes by.
     
  3. UTmotorbiker

    UTmotorbiker New Member

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    Thanks so much for your reply. I appreciate that. So with my 41T rear sprocket and the motor broken in it should cruise 25-30 then pretty easily? I've gone 30 on the bike a few times before and I'm not too sure I wanna go much faster than that ;)

    Any recommendations for upgrades that aren't too costly? I am using this bike as a somewhat replacement transportation for my car. I haven't bought gas in almost 2 weeks. I love it!
     
  4. Greg58

    Greg58 Well-Known Member

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    25 to 26 is what I cruise at on my 48cc bike, my son in law and I did over 45 miles last Sunday and most was at that speed. Both our bikes have the 44 tooth sprockets. Are you sure your speedometer is correct? If its a bike computer measure the tire size in mm and use that number, mark a line on a flat surface and align the valve stem with it, then role the bike one wheel revolution and mark that. Measure the distance between the two marks with a metric tape measure and you have the correct number for your tire size.
     
    #4 Greg58, Oct 12, 2014
    Last edited: Oct 12, 2014
  5. Henshooter

    Henshooter New Member

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    One important thing I've learned ( but opinions vary ) is to not mod your engine until after breakin ,also you will hear from time to time sellers of the motors ( not all mind you ) stating things like go the racing carby or this will make it faster ,you will at some point get burned by listening to this IMHO.

    I would start by gauging your own engines performance and character because trust me on this each and every engine has a personality that differs from the other
    My current kit hates warmup ,runs like a pig until it's at correct running temp but when there she screams along and easily does 35mph without any real mods ( I run a 32 t though) .

    I would start with changing the spark plug lead for a good automotive one , rejetting and adjusting fuel to air ratio ,to get her running nice and clean and soldering the electrical connections ,yes you might not get her to run much faster but she will fire and run smoother ,then think about mods to increase speed and performance ,small steps first my friend

    Regards Henshooten
     
  6. Davezilla

    Davezilla New Member

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    I agree with HenShooter's recommendations, even tho they don't add power or speed, they do add reliability... The rejetting can add power tho if yours is running too rich or too lean, there's no size I can recommend because a lot depends on other conditions like outside temperature, altitude above sea level, and any engine mods etc will change what jet size your engine likes. Some like to solder the main jet shut then re drill and others like to have a collection of jets to swap out until they get it right... both methods work, but drilling tends to be the most accurate when one size is a bit rich and the next size down is too lean etc..

    for the sprocket size, if your bike reaches top speed quickly and it feels like the engine is running out of rpm when it feels like you should be going faster, it's time to go to the next size smaller sprocket, if it accelerates sluggishly and feels like it's struggling to go faster then it needs to be geared down with the next larger sprocket. Going from a 44T to a 41T is enough for you to feel a difference, but if you live on flat land with very few hills, a 36T may do better... The way the engine is set up will also be a factor in what rear sprocket size you want, an engine with decent torque and doesn't rev past 6k rpm will do better with a small rear sprocket than a 8000 rpm screamer with less bottom end torque but good top end power.

    As far as the most bang for the buck mods goes, a good expansion chamber pipe will deliver and can be tuned for more bottom end or more top end by the header length.

    The stock NT carb works great with nice all around power, it's also simple and reliable, no real need to upgrade the carb unless you're looking for big power at high rpm's, then a Mikuni VM 18 or Dellorto PHBG 19 or 21mm carb work really well. They do require some tuning to get right but make good power once dialed in.

    The stock CDI unit also makes good power but the weak link is the spark plug wire and boot, replace with a decent 7mm automotive wire and boot. The HD Lightning CDI is a really good choice for aftermarket.

    For the cylinder head the stock one is way too small for good heat dissapation and has poor compression in stock trim, you can shave off some of the head to boost compression and power, but it still don't do much for keeping cool... The fred head, Diamond head or a Puch Hi comp head work really well here... excellent compression and much much better cooling.

    A ported jug and indexed piston will make even more power and you can buy them from a few vendors in here with decent results, Fred's jug and piston combo work well and so does the Arrow ported cylinder and piston sets, or you can read up on the subject and do your own porting, Mainly cleaning up the casting flash from the transfers, widening the intake and exhaust will give noticeable results, but for more rpm and power you can alter the port timing but that's a much more in depth subject... people in here can help once you're ready to go that way.

    Start off with a good pipe and maybe tune the carb, and then a better head and you'll have a nice noticeable gain, then go for a ported jug and indexed piston for the next step if the bike still isn't fast enough for you..
     
  7. UTmotorbiker

    UTmotorbiker New Member

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    Hey guys, thanks for the info. I have been doing a fair amount of research and I have heard a lot of what you guys have been saying. I live in a pretty hilly area but I'm hoping that the 41T will still let me climb the hills and give me the boost in mph I'm looking for. I kinda get the sense its running a little rich and guzzling gas a little more than it should be. Any recommendations?

    My bike runs sluggish when its cold but then picks up speed after warming up. However I don't feel like it ever revs up that high and I'm hoping there is some little tuning things I can do to help it run a little better.

    Thanks for the info guys!
     
  8. UTmotorbiker

    UTmotorbiker New Member

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    Oh I also live at 4200 ft above sea level so I'm sure there needs to be some sort of adjustment made for the altitude. What needs to be changed to make it run better?
     
  9. Davezilla

    Davezilla New Member

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    At 4200 feet above sea level leaning out the carb would help.. You can get smaller jets for the carb or you can get some small drill bits and solder your main jet shut and re drill it to match your altitude. I've heard a #64 jet would be a good starting point and tune up or down from there.
     
  10. maniac57

    maniac57 Old, Fat, and still faster than you

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    Once you have run at least three tanks of fuel through it and the engine is fully broken-in. it's time to jet it properly.
    Most china dolls come FAR too rich from the factory and tend to four stroke badly on top end.
    Try dropping the main jet size down. (Most of mine have wanted at least two sizes smaller, sometimes three)
    I can't tell you the numbers since I solder and drill my own jets using wire guage bits for consistency. You buy five jets labeled .70 and you often get four or five different size jets. Drilling them is easy and free.
    Remember, if it only four strokes at full throttle, you are on the main jet only. If it pulls hard to the top then blubbers and four strokes, drop the main size till it pulls hard all the way to your rev peak. Don't forget to reset the needle with all main changes for max tuning range. I drop a jet size, then start from full rich on the needle, Checking one slot at a time until the engine feels happiest.
     
  11. Davezilla

    Davezilla New Member

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    I agree on the jet size issue... these jets aren't drilled very accurately so investing in a set of small gauge drill bits, a pin vise, and even a set of jet gauge pins to verify the size of unknown jets or if you have several jets drilled and need to know which one is which...
    Definitely let the engine break in before trying to tune it as it won't behave the same or make full power until after at least 3 tanks of fuel.
     
  12. UTmotorbiker

    UTmotorbiker New Member

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    Ok, that sounds great. My engine only has about 55 miles on it so far but I should have it broken in in the next week or two. I will refrain from trying any mods except the 41T sprocket until that happens but I definitely think cruisin at 30 mph will suit my needs quite well. I only use it to commute from school and work and back, both of which are under 3 miles away.

    Okay, so one last question... what do you all mean when you say it's "four stroking?" I have been trying to figure out what that means and how to diagnose it on my engine but I honestly have no clue what it means when you say that. Can you give me some easy to understand language that describes that? I am definitely a newbie when it comes to 2 stroke engines and fairly new to the motorsports in general (although I have ridden 2 and 4 stroke dirt bikes before, but not for some time).

    Thanks guys!
     
  13. nelsonk1969

    nelsonk1969 New Member

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    Hi 4 stroking is a term used when a Two stroke engine runs poorly and fails to fire the air fuel mixture consistently.
    if you keep your mods well planned your engine tuned and decarbonized you will not likely encounter this problem.
    color tuning is a way to insure your Air fuel mixture is set correctly
    I have used this kit many times on motorcycles I am not sure if they have the size that will work on your Two stroke motor.
    http://www.carbtune.com/colortune.html

    You can also go old school and simply read the spark plug as it a good indicator of your current tune.

    and never take for granted that all the basics are good as a slightly dirty air filter can starve the motor of air making the engine run rich.
    if you have a dirty air filter you don't want to cure it by filling in your jets and drilling them out smaller. same goes with the fuel filter if you have one and you do have one right?
    if the fuel filter clogs up and starves the motor of fuel this is no reason to drill the jets bigger.
    Keep it simple and make sure the bike is at its peak before you start to modify it as many poorly planed engine,exhaust and or carb mods will leave you with feeling that you were better off when it was stock.
     
  14. Greg58

    Greg58 Well-Known Member

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    When a two cycle engine four strokes the engine sound changes sometimes, kinda like a flutter or a lawn mower. The bike I ride most four strokes a little till it warms completely, you can hear mine four stroking in the first part of my video of the red oak covered bridge ride part 2.



    http://motorbicycling.com/showthread.php?t=57066
     
  15. Henshooter

    Henshooter New Member

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    I heard a good explanation of four stroking ,it's not 100% accurate but non the less fairly close to the description , that is China girl four stroking sounds like a Harley with a 5000 lb elephant on it ,yes it's loud and it pops but it just ain't going nowhere ,a good chinagirl that doesn't fourstroke sounds like a sweet symphony of explosions ,something like a shot of good whiskey ,smooth right the way through with a good kick at the top end
     
  16. steveanson

    steveanson New Member

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    My suggestion would be to learn to read your spark plug after your breakin. I don't have extensive experience with these little two strokes, but have tuned racing go-kart engines for many years. Your plug can tell many tales about what's going on concerning combustion...Steve
     

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