New Member, first build. 80cc china girl on a fixie

Discussion in 'Introduce Yourself' started by jerrywelz, Jul 23, 2014.

  1. jerrywelz

    jerrywelz New Member

    Hello everyone!

    Here is a quick introduction, then onto the pictures =). I'm jeremiah, lived in southern California for most of my life. I spent four years traveling the world in the USAF doing fuel systems repair. I'm out now and currently working for the grocery store. this is my work commuter bicycle. 8 miles one way every day.

    I bought a kent fixed gear from walmart for $120 and ordered the 80cc 44t china girl kit from ebay.

    Originally i tried to run the 18t fixed gear and it barely ran. I had to pedal up the most minor of hill to keep the engine from stalling out. she was also four stroking badly all through the RPM's with the C clip on the leanest setting on the NT carb needle.

    Couldn't get to work like this so i swapped the 44tooth and it was ride-able.

    After i adjusting the float to the proper 21mm, opened up the obstructed steel intake and exhaust manifolds, she ran even better but was still four stroking.

    I decided more oil would help with the overly rich engine. My understanding is that the main jet is too large and causes the engine to bog at almost all throttle settings. adding oil makes the fuel more dense therefore less can flow through the main jet leaning out the engine.

    Anyways i mixed some 12:1 tcw3 and did some minor port work. i thinned out the transfer ports and took a few mm off the top of the exhaust. Also cleaned and slightly enlarged all the ports. in hindsight i probablly lost torque. I also polished the exhaust port and abraded the intake.

    The bike ran so damn good like this until i crashed it. hit a curb head on and bent the frame and rear wheel. I decided to just get a new identical bike from Walmart because this is how i get to work.

    Engine ran so good i decided to try the 18tooth again. the bike is slow off the start but can still climb hills. I hit 39 tonight on a small downhill road.

    I need a permanent air filter solution and would like to jet smaller so i don't have to run sooo much oil.

    I'd imagine the manic mechanic sprocket adapter with a 30tooth sprocket would be scary fast. thanks for reading guys. all input is appreciated. looking for tuning advice or tips. however i am constantly searching the forum and reading about areas i want to improve on and i', headed in the right direction =) thanks guys!

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  2. jerrywelz

    jerrywelz New Member

    here is the best picture i could get of the plug. my camera died

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  3. butre

    butre Well-Known Member

    I'm glad someone tried the flip flop hub idea, that's something I've been considering for a long while but didn't want to invest that much in a potential flop. I might try the same thing on my next build.

    what's with all that red junk packed between the fins?
  4. HeadSmess

    HeadSmess Well-Known Member

    ^^^ the red goop apparently reduces noise but doesnt really ;) you see it on old school air cooled twostrokes, proper rubber things to stop those super thin fins from singing.

    do NOT try a 30T, especially if they be 700c rims, which they appear to be? nice choice in tyres but! nice and solid looking :) dont use them skinny racer ones! (edit...they are, i see the sticker on the frame now)

    i know from experience, you can *just* get away with a 36T. welded it directly to the inside of the fixed sprocket.

    at the moment, i smell like wd40 and am cursing bikes again, as im just lacing a 3speed hub in, and have just realised i have 36 (also a 28 in the pile?!) hole hub with 32 hole rims... i guess i have to pull my only 36 hole 700c rim apart.... a real nuisance, but rather normal when dealing with these silly things! hoping i dont need to replace my spokes when i do... im thinking i might invest in a thread roller, as i get annoyed every time i lace up a wheel. $160 or so on fleabay. OUCH! but worth it as spokes are around 60 or so a set here...

    ill be using a 44T this time. i was thinking of just replacing the current 36T with the 44T, but it appears the hub is starting to strip out, and its only been a few weeks. considering the sprocket runs on a right hand thread which will loosen off under power, and is locked by a smaller od left hand thread, i cant rely on it. im going back to plain old rag mounts.

    unless i make a hub adaptor thingy, which i really couldnt be bothered doing. dont worry, i shall regret being lazy later on as normal, but hey... the spoke issue already has me annoyed enough as it is for one evening!

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    Last edited: Jul 26, 2014
  5. HeadSmess

    HeadSmess Well-Known Member

    i thought my frame was cheap! it is! but it has v-brakes! anyways...note the size of that was ok for 26" rims, but is slightly lacking on hills with 27"... :( still good for 70km/h but!

    im surprised you can even get it started with that sprocket you have!

    if you wanna go for "rag mount" sprockets, just note the number of spokes you have....need 36, or need to get a sprocket with 8 holes.

    oh yeah. check all the frame welds THOROUGHLY. possibly even think of stripping it down and gussetting them, like i will be doing soon. hopefully BEFORE it collapses on me! :jester: i noticed a few, erm....blow holes in the headtube/downtube welds....can you say CHEAP and NASTY?

    i hope that spring on your tensioner is just an assistant and you tighten the bolt up good! good idea but ;) ive had a tensioner tear out half my spokes at speed before, and its not the most pleasant of experiences. so make sure its tight!

    replace the chain, which youll have to do anyway now, but use a heavy duty bmx chain, as space is limited if you try using 410 or the chain they supply... in fact, im going to be finding out if theres actually enough clearance for the 44T soon! more than likely, the answer will be no, but hey...only one way to find out!!!!!

    my choice of chain on these things, note it only goes on one way(really? im just saying it does), and requires a chain tool. in reality its the only HD chain my local shop stocks and i couldnt be bothered looking for alternatives :p also available in neat-o colours :) the half link means you can sometimes avoid the tensioner altogether, but its good for taking up slack. really, i prefer standard type links...

    Last edited: Jul 26, 2014
  6. jerrywelz

    jerrywelz New Member

    Headsmess, thanks for your insight! i was planning on replacing the chain and will go with the heavy duty BMX. I've also read horror stories where the tensioner kissed the spokes.I made sure to install it more than snug, it's super solid where it's at. the spring does tension the chain, but the bolt and lockwasher are what's holding it there.

    i just ordered the 36t sprocket and rag joint, but after reading your post i will try to run it without the rag joint if possible. I deliberated between the 41, 36, 32, and 30 tooth. If i can get around and even make it up hills with this 18t i'm sure any choice will be an upgrade, but the 36 seemed ideal.

    I cut ramps into my piston where the transfer ports are. I was hoping to improve mid range and torque. the ramps help but need to be perfected. the angles are not quiet exact because i don't have the tools or knowledge to measure and cut each ramp exactly the same. one of the ports is opening a hair earlier than the other causing vibration.

    I ordered a new piston kit and will try to perfect the one i have. pictures on all these internal mods will be posted next time i take the jug off again.

    how does that pipe run headsmess? did you fab it yourself? it looks like it performs well. ever consider wrapping it for a cleaner look?
  7. HeadSmess

    HeadSmess Well-Known Member

    wellll, i maded a video the other day, that didnt really turn out as well as planned,(i got potholed at the least....i posted it on here none-the-less) but...

    the pipe rips :) when i get this 3 speed on ill make another one. video, that is. i need a decent camera mount.

    used 2 stroke wizard pro for the dimensions, v5, with his "duel power" extension. basically inside that reversion cone is the cone that was initially calculated, but made out of perforated sheet. in theory the internal cone sets the main rpm power band, and the extended outer cone gives a lower rpm band to boot. i found stuff that was around 50% open area, so i get about equal bands. ie, if it was 30% open id get more of the high band, if it was 70% open, more of the low band. i havent really done much fiddling on that side of things, takes long enough to make one as it is!

    but i did make it without the extension as well, and there is a definitely noticeable effect down low! i got two power bands :)

    i think, from memory, i tuned it for 8Krpm. puter blew up and i lost all my notes :icon_cry: it feels happy there, anyway. like it hits a wall going any faster. i blame that on porting.

    erm... i sorta painted it black the other day? :)

    oh. i prefer letting the thing rev out, i like the sound of a 40T, but its either 44 or 36. im going for 44. what i have on hand, of course :)

    just waiting for the postman, then i can sink my dentist drill into some ports :)
  8. KCvale

    KCvale Motorized Bicycle Vendor

    1/2 link chain, I sure didn't like the stuff.
    1/2 links are a pain even on regular chain, a whole chain made of them was no fun, and yes they are directional, the skinny part of the links faces the direction of travel for much the same reason you always put the closed end of master link clip facing the direction of travel, if it hits something it won't catch.
  9. snoopdog

    snoopdog New Member

    the spark plug definetly shows signs of not enough oil in the fuel mixture. check carb throttle pin adjustment if u know how to set this. also add more oil to your fuel mixture. i put 3-4 caps of oil per liter of fuel. also i like the spring idea on the idler but im not sure it will last especially on bumpy roads like here in africa, where i live, where the roads have many pot holes :p
  10. jerrywelz

    jerrywelz New Member

    some pics of where we are at currently.

    got the banana pipe and sha carb

    I put the NT carb jet into the SHA as the jet was too large. still four strokes at WOT, but the NT carb used to do it as well. maybe i need a smaller jet? I'm running a 12:1 mix and the plug looks about right. Is there any reason why i need this much oil for the engine to run right?

    I put this tubing on the banana pipe and it seems to cut low end power, but increase top speed. any thoughts?

    thanks! IMG_0085[1].jpg IMG_0088[1].jpg IMG_0089[1].jpg IMG_0079[1].jpg
  11. jerrywelz

    jerrywelz New Member

    few more pictures, shameless bump on the question about the mixture!

    I am running a stock NT jet, SHA carb, banana pipe, 36 tooth sprocket mounted to the fix gear with the rag joint (solid).

    the Bike four strokes pretty bad, always at top speed WOT and sometimes through all RPM ranges. Once the engine is warmed up it 2 strokes in the mid range and always when climbing hills.

    I've got the Champion CJY7 plug with 2 washers on it so it doesn't contact the piston. tried running the b7hs and it ran poorly i don't think the NGK sits far enough in the combustion chamber.

    i'm running 12:1 2 cycle sport oil by masterpro with 91 octane. the engine is broke in but if run less oil the bike will bog even worse. do i need a smaller jet to run a leaner oil fuel mix and not four stroke at WOT?
  12. jerrywelz

    jerrywelz New Member

    don't mean to double post but i forgot the pics
    IMG_0092.jpg IMG_0093.jpg IMG_0094.jpg IMG_0095.jpg
  13. HeadSmess

    HeadSmess Well-Known Member

    some may argue the point, but im ferpectly happy with 50:1 oil mix, contemplating changing to 100:1 for a while just to see what happens.

    nice to see a reasonable looking sprocket on there now :) take a link out of the chain and readjust the tensioner or its gunna cause a nasty accident! and it wont be to a bystander ;)

    (edit....looks like you pre-empted me and have already done so ;))

    i gave up on the 700c wheels altogether, had way too many flats, a wheel collapsed on me, and well...i prefer the ride on 26" mtb tyres. the poor old trusty shogun came out of storage :) roads are really bad around here...

    all i can say with the effect of adding some pipe to the pipe... the banana pipe itself is tuned (if its tuned at all?) to peak at about 12000 with the port timings on these engines. so they do sweet f all down low(but more than the stock exhaust, if thats any consolation?). adding some length to the stinger will increase back pressure slightly, which assists for power up high. more noise than genuine boogie fever, them things... now, if you were to get your stock muffler, cut the can off, and welded the banana on that length of header pipe instead...then you "should" get a noticeable powerband.

    yup. smaller jet required. way smaller by the sounds of it... the plug isnt the issue. a box of micro drills, a pin chuck, and some solder, and away you go :) im happy with 0.55, but whats ideal is engine, rider, and atmosphere dependant! or, just start inserting very fine copper wire into the jet, one at a time, carefully tacking them in place until it feels right.

    i now would feel safe with ngk 4, after discovering a champion with the equivalent of an ngk 2 (rj19hx) causes preignition after extended full load runs. ngk b4hs is probably not commonly available so ill stick to using whatever looks like it will do the job :) and seriously...i use whatever looks like a spark plug with no discernible differences in running, unless its one of those nasty chinese junk plugs. they just land in the bin depending on how drunk i am at the time :wacko: so, champion l82y, cj8,rcj7y, um... ngk bpmr6hs, b5hs, br9hs, (even bushed out to take ngk b5Es at one point) whatever, they all run much the same bar that one particular plug. its a very very hot plug, stays spotlessly clean no matter how rich the mix (the plug is only a good mixture indicator WHEN THE HEAT RANGE IS IDEAL, jet by feel, not plug colour)...but just doesnt appreciate the way i ride/jet (as lean as i can get it and still hold WOT). it came from a mower, and back into the mower it has gone.

    as for depth in the chamber... i can run a good old cj8 that is about 3 threads too SHORT, without the projected tip, with no issues. in fact, the projected tip plugs, while logically seeming better, actually arent as the flame kernel is too close to the piston crown. all good with these engines, not so good with highly tuned and stressed engines, so really, its a moot point :)
  14. jerrywelz

    jerrywelz New Member

    thanks for all the time invested in your reply's HeadSmess. I appreciate you sharing the knowledge/widsom.

    I know the direction to go with the spark plug. I can't really fabricate much here for the exhaust. I only have access to basic hand and power tools. I can understand your vision for making this pipe ideal and giving it some more torque and useable power band.

    On the wish list for fridays paycheck:

    Air filter, i'm planning on this

    I've got some jets in the cart @
    I plan on ordering 54-68 ish

    I found what appears to be the perfect tensioner sprocket on ebay. There are a few options here

    I hit 38 downhill today 4 stroke thumping the whole way. Can't wait to get everything dialed in. The air filter with proper jetting should make things significantly quicker. The sprocket tensioner pulley should increase longevity. Then i'll start messing with the pipe, I'm considering a pocket bike exhaust.

    The never ending project continues :D

    Edit: it's 2:48am and raining here in Southern California. This motorized bicycle thing is quite addicting. :D

    Edit Edit: I could probably save my $$ on the filter. the pantyhose filter works well on this carb because it can accommodate the adjustable clamp.
    Last edited: Aug 20, 2014
  15. jerrywelz

    jerrywelz New Member

    Brainstorming. exhaust keeps coming lose, i need some better lock washers and i'm gonna use red locktite this time.

    some pics:
    IMG_0098[1].jpg IMG_0099[1].jpg

    ran out of gas intentionally today on the way home. switched over to some echo powerblend full synthetic @ 25:1 89 octane it's ISO L-EGD and JASO FD certified. supposedly the second certification is Japanese and ensures sufficient detergent to keep the rings from sticking on our hot running engines. the marine or ash-less oil which is what everyone is selling is supposedly bad for our engines because it has zero detergent, cooler running water cooled engines don't need it.

    the bike feels MUCH quicker compared to the 12:1 conventional i was running before. it actually seemed like it 4 stroked less?

    Anyways I ordered some 5mm 50-68 dellortos from the UK for $16

    gonna cut the header off the banana pipe tomorrow and the can off the stocker. i'll try using brass pipe, metal clamps, and heat resistant tubing to hold the two together
    Last edited: Aug 22, 2014
  16. jerrywelz

    jerrywelz New Member

    got the brakes all sorted. they work good now with the dual pull handle (important)! I took Head's advice on the pipe and i'm very satisfied, the bike has torque now.

    aome pics. my friend gave me the aluminum exhaust spacer.

    IMG_0105[1].jpg IMG_0104[1].jpg IMG_0101[1].jpg IMG_0100[1].jpg IMG_0057[1].jpg IMG_0059[1].jpg IMG_0018[1].jpg
  17. HeadSmess

    HeadSmess Well-Known Member

    :) someones found the "rohmell roll your own" ;)

    why is the scr so black? looks like it was tack welded on!

    pot the thing up in some polyester/epoxy cus boy...they can BITE!

    not sure if you can see it on this pic, but thats whats running this lil sucker on the stand :) made it from an old bug zapper :) (edit...oh yeah, nice and IS covered in resin but)


    might have to transplant it on my ride now, i need it! the black box has had enough and died on me! something always goes wrong just as im almost home...almost.
  18. jerrywelz

    jerrywelz New Member

    I'm not sure if my DIY CDI works, tried using it when my magneto coil was bad. the scr is black because i was soldering the heat sink to it.

    I'm currently having trouble with flats on both tires. does the DIY CDI work better than the stock china one?

    what purpose does that china girl serve? your very inventive man! i'm still 4 stroking @ WOT, currently opening up the exhaust port more. i've read your posts about the wire in the jet. still don't fully grasp how i should put it in there though :idea:
  19. HeadSmess

    HeadSmess Well-Known Member

    they work, thats about all i know so far, or care about. and will take just about ANY type of ignition coil ive thrown at them :) the scr doesnt need a heat sink. its only on for a very brief time. well within their ratings. (i tested one out with a standard AC was the 1watt, then the 5watt resistors that fried! but works on the engine with 1/4 watt ones fine. duty cycles i believe. ) if you made it per the instructions, it will work, and works at a much lower voltage to boot :) remember it needs a separate ignition coil.

    its my dyno brake in the making, the threads in "performance mods".

    just waiting on a tacho still so i can start testing various things out, rather than the standard forum board system of some truth getting all mixed up with a lot of complete and utter B.S., with absolutely no real conclusive evidence. :) definitive,un-biased answers. and im perfectly willing to destroy engines in the process :) it saves removing and re-installing the engine in a bike for each and every test, of which i have a LOT planned. id leave the exhaust port alone for now, btw ;)

    wire in the jets... very carefully? with a small soldering iron... i dont actually have a pic handy... i got drills. try to tin "just" the top and bottom edges of the jet, tin the wire, thread it through, and then simply bend it over and tack in place.

    flat tyres is why ive gone back to 26" wheels. smoother ride, less flats...haha. i just had a flat the other day :rolleyes:... pot hole induced flats would be more appropriate. cant avoid nails or screws still! :) (or keys. yes, i once had a flat on my motorbike that was caused by a KEY!)

    this must now be one of the longest threads in this section of this forum board :)
  20. jerrywelz

    jerrywelz New Member

    i guess it's long because i'm always going at it. looking at the progression of the bike makes me smile. haha. sooner than later this thing is gonna be bullet proof.

    here are some pics of what's going on tonight. off work tomorrow so i have time for it and my girlfriend. gonna get the whole tire tube thing sorted.

    that dyno brake looks sick. i'll have to read your thread. i'm gonna solder the jet tonight, i have acces to many different types of wires. looking for a REALLY tiny one

    IMG_0111[1].jpg IMG_0112[1].jpg IMG_0113[1].jpg IMG_0114[1].jpg IMG_0115[1].jpg

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