Carby Keihin carb clone

Discussion in '2-Stroke Engines' started by SRPM, Apr 20, 2016.

  1. HeadSmess

    HeadSmess Well-Known Member

    arrrgh, this thread is confusing... certain someone that cant use punctuation or spaces doesnt help much... do you think he ever reads what he has written to make sure its comprehensible?

    i now see that YOU are the OP ;)

    the port work... the cut out above the intake port should be flush with the transfer ports, or marginally lower. called a boost port. the transfers sort of squirt air/fuel to the back of cylinder, away from exhaust, over the top of the piston, and the boost port then squirts out and pushes the air/fuel to top of cylinder, as exhaust gas is pushed down and out the ex port... it should be very steep, and fairly shallow. its not really a transfer port, more of an assister.
    combined with a good expansion chamber that tends to "suck" on the exhaust port, it allows the reeds to open and allow more air/fuel in, rather than rely simply on crankcase induction.

    rather pointless if it doesnt have the right exhaust.

    problem is that you dont know whats happening inside the cylinder when its running, you need to have a flowbench and smoke-machine, combined with a clear head to really SEE whats happening, and have the engine spinning at operating speed...tricky. theres no point just chopping metal away if you dont know whats happening in operation. its like throwing darts whilst blindfolded. the angle, the depth of notch, the difference between it and the transfer ports...all very critical. guessing doesnt work.

    the cut out below the intake port is simply to bypass the piston port closing, allowing air/fuel to enter the crankcase for the maximum amount of time.

    have you actually ran it without the reeds with all this port work?

    exhaust was it only widened or has it been hacked into and raised? edges properly bevelled or just left as machined?

    have the transfers had any work such as removing casting flash? any changes in the angles?

    probably better off getting a new cylinder and starting it all over from scratch again, go back to stock carb, etc... 35mph (i speak km/h...60 was average) is about what i get with UNMODIFIED 48cc engines. just an expansion chamber. the only bolt on modification that really DOES ANYTHING.

    when working on the intake side of things, its best to remove the exhaust ENTIRELY so you know it has no affect on things. then you can make some sort of judgement on results. you then modify the exhaust to compliment the intake.

    reedvalves do not improve top end performance. just the mids and lows.

  2. SRPM

    SRPM Member

    All post are from my phone, I try my best to make it legible. Sometime I rush through my post to get back to whatever else I'm doing. Sorry for the unconvince.

    I did none of the port work, it came that way.

    No, why would I.

    Exhaust looks widened.

    Getting expansion chamber at some point.
    Last edited: May 8, 2016
  3. HeadSmess

    HeadSmess Well-Known Member

    yes, that is what you said... i can read.
  4. SRPM

    SRPM Member

    "probably better off getting a new cylinderand starting it all over from scratch again, go back to stock carb, etc..."
    Is what you said. I can read too.:eek:
  5. HeadSmess

    HeadSmess Well-Known Member

    yep. at least then you know where you are starting from., without having someone elses failed experiment cluttering up the place.

    30 mph is what they do, stock. so what benefits have you reaped?

    learn to WALK before you FLY.

    get the expansion chamber, and forget about the carb for now. and maybe forever.
  6. SRPM

    SRPM Member

    Have you even read this thread all the way through?

    Jeffery gagnon may need to but my bike is fine.
    Why would I start with new jug and everything when I just bought the engine.
    I just needed help with the carb and tuning it, but I helped myself since I seem to be the first one to buy this engine.
    So let's help Jeffery and anyone else with the carb or engine.... gt80 by the way people from... you guessed it gasbike. boooo. Oh well runs great.
    Last edited: May 8, 2016
  7. HeadSmess

    HeadSmess Well-Known Member

    so, in a court of law, you would say that this WASNT your writing?

    have you run it since removing the reed valve?
  8. HeadSmess

    HeadSmess Well-Known Member

    dont worry, that was directed at gagnon that seems to write one big mash of words with no pauses for breath, so to speak.

    what you write seems to make sense except i cant figure out if its currently running or not, whether it has reed valves fitted anymore or not, and yep...thats about it.
  9. SRPM

    SRPM Member

    It is running. It has reed valves fitted. It smoothed everything out shown by the arrows. PicsArt_05-08-11.14.02.jpg.jpg
    I have not even started the engine after this.
    What lead to this was I had removed the spacer behind the reed valve (somone mentioned to me that it was of no use and would boosed crank pressure if removed) that cause a leak covered in my other thread. And I had to put the spacer back on.
  10. Rob H

    Rob H Member

    Also if you are running hi compression u really ought to be running hi octane I buy 5 gallon drum of 118 and mix it with a little pump gas you would not believe the difference night and day
    Neptunati likes this.
  11. SRPM

    SRPM Member

    Where do you get that, whats it called, how much is it, and how do you mix yours....?
  12. SRPM

    SRPM Member

    I was thinking of trying the premium at the shell station but idk about that, I heard ethanol is bad for these engines. Does anyone know of a station that sells non-ethanol gas? Has anyone tried the premium from the Shell gas stations and are currently using it?
  13. HeadSmess

    HeadSmess Well-Known Member

    now this threads starting to get somewhere.

    tuning issues. firstly. mount the carb solidly. if its buzzing or shaking around, the fuel will froth in the bowl. you cannot tune it if its doing that. nylon ties arent really up to the job. some type of bracket, or get someone to weld you up a new adaptor from reeds to carb flange. scavenging say, the bend from some bmx handlebars should get you the clearance AND be the right size. no point port matching one side if the other side lets everything down. one, smooth continuous piece. let the carb work properly!

    mikuni and keihins have one thing in common...there are soooo many options available besides just jets! mainly needles... different lengths, thicknesses, tapers... really really complex to get right but a sheer joy when they ARE right!

    i havent read anywhere anything about doing plug chops in this thread...? get a new, ngk b(r)5hs or similar. can change to a 6 or 7 later n, but 5 is good for plug chops and most riding.

    the carb tuning link already posted and a few others are the best things to read, otherwise i am just repeating them, so i wont. other than, start with the main jet, and find the pdf of jennings "2 stroke tuning"(google...pretty common) and read the part about carbs. one important part is to make sure the needle jet is big enough before doing ANYTHING. pretty simple... remove main jet(yep, take it out), needle on middle clip(if it has one... a lot of keihins use washers and a fixed needle.) then try to start it.

    if it wants to rev at all when the throttles opened...the needle jet needs opening up. if it bogs down, splutters and dies with a wet plug...GREAT! you can go back to jetting.

    ethanol smethanol... while i wont run it anymore, simply because my road bike seized up whilst i had a tankful of it...the condition was pre-existing and not caused by fuel.

    despite the 11.5:1 compression revs harder on 91 and 95 compared to 98.

    there is nothing that can be damaged by ethanol in these engines.

    using high octane fuel is pointless, a waste of money, unless you enjoy running full throttle at very low speeds (lugging up steep hills with too high a gearing) or have a ridiculously high compression ratio.

    maybe once you fit a decent expansion chamber, then you can use the expensive stuff, but for general use... low octanes produce more power.
  14. Rob H

    Rob H Member

  15. Rob H

    Rob H Member

    U can order it on eBay there are many brands I last bought Torco 118 most hi compression motors will hardly run on pump gas
  16. Rob H

    Rob H Member

    It's really expensive but you will not get the full potential of your motor without it
  17. SRPM

    SRPM Member

    Thanks for the info. We should talk more about these carbs and needle jets and pilot jets and there's another jet but can't think of name.

    I've basically got the main jet solid, just a little confused about the other jets. Like how to set them, where to get them and do I really need to.
    It's strong off the line and I think mid range and kinda loses it at the top not as much as before tho.
  18. SRPM

    SRPM Member

    Not really looking at putting race fuel in my China doll.
  19. Neptunati

    Neptunati New Member

    Sorry you couldn't get that leak figured out. Also I'm pretty sure they put the spacer in so there reed setup doesn't look exactly like the design they ripped from arrow lol. When I get mine altogether that crude aluminum block won't be there. And yes less space between the carb and piston equals more crank case psi, or so I've read seems logical. Also sir headsmess it's a possibility that ethanol and aluminum or aluminum alloys might not like each other. I fix a lot of mowers and have seen two brigs carb bowls with pin holes from what I've been told was ethanol corrosion. But I've no proof that that's what caused the holes. I still have one of the bowls just cuz I couldn't believe it lol. The guy at the local mower parts place said he knew for a fact ethanol eats aluminum, but idk.
  20. SRPM

    SRPM Member

    Well just got 91 octane from gas station, couldn't figure out if it has ethanol in it or not. It was an older station so hopefully not.
    Might have to do some more tunning to get her to sing up hills like she should. Drives me crazy just go up the hill:(