Carby Keihin carb clone

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

  1. Steve Best

    Steve Best Well-Known Member

    You missed the point.
    I'm not using a paper to back up any sort of "belief".
    I used it as a starting point for learning.

    Gordon Jennings is a brilliant and thorough writer and researcher.
    He explains his thought process, his reasons, what he did and what he found.
    I absolutely believe him that if I want maximum power in a 1970s Suzuki 250 on castor oil, more is better.
    Are we in the same place with our China Girls?

    I laid out my thoughts, what I did, what I found, and the conclusions I drew from the results.
    We need to do more of that, rather than just relying on old paper. Facta, non verba, you know?

    Many of your webpages do exactly that:
    Lay out the reference material, what you did, and the conclusions you drew from your results.
    I am very grateful for the work you have done there.


  2. jaguar

    jaguar Well-Known Member

    I see your point but don't think it's wise to discard his findings just because your 2 stroke is not exactly the same as the one he used for testing.
    Some findings are universal in their application.
  3. Chrisxman1

    Chrisxman1 Guest

    Dude i have same sluggish problem with carb. Final conclusion. Not enough air. Havent adjusted but try this. Shut the fuel line off then run it for a minute. Keep running it and just wait. It will top end out. Awesome
  4. Chrisxman1

    Chrisxman1 Guest

    Oh yea. Hahaha. Want a quick ride. Get you a can of whipped cream. Put a filter on a hose and run hose from can to air intake. Get it maxed out in rpms and hit the valve on whipped cream can making sure its upright. Pure NOS and dirt cheap. Hahahaaaa
  5. Do search gt 80 jets then kings motor or has but if you search site it will only show up nt jets why I know? Just do general search. Good luck mine keeps revving even when you let off gas waiting for smaller you get slow and mains 24.99.
  6. No one is vent and is over flow you even need to use if you plug them or hook them together motor cause it needs vent to allow gas to enter carb
  7. wagonrdRuss

    wagonrdRuss Guest

    Russ says: I may be too late to get in on this discussion, but here's what I found. I have the GT 80 racing engine with the keihn carb clone from I operate at 7000 feet altutude +- 2000 feet. My motor pulls 15% grades with a 56 tooth rear sprocket. The main jet is 62 and the slow jet 52. Jets from jetsrus from the N424-24 listing. The motor four strokes from idle up to about two thirds throttle, then...when going up a steep grade with wide open throttle, the engine "sings", just like a 2 stroke should. I've tried smaller slow jets (50, 48, 45,40) and the engine "sings" at the lower RPM's, but bogs down from too lean a mixture a wide open throttle. So, I have a needle problem, but cannot find anyone who sells the 42.11mm needle (length L1 as measured from the top ring to the tip), and also I must step up to a larger main jet if I find a needle. I think this present state is the best I can do with this Keihin clone. I'll just put up with the lower RPM four stroking and be satisfied that I can climb most mountain roads here in the Eastern Sierra. However I'm experimenting with the Walbro HDA 48D 502 carb. My chain saws use the walbro carb and they really work well at this altitude. These carbs have adjustable jets. They require a pulse line from the engine crankcase to the diaphram in the carb, and neither the engine nor this carb have pulse line connections. But I'm closing in on solutions.
    Last edited by a moderator: Nov 2, 2016
  8. jaguar

    jaguar Well-Known Member

    Assuming you have installed the right size idle jet*, lowered the needle all the way, and have a non-restrictive air filter then you need to get the Keihin jetting spreadsheet at
    and figure out which size needle you need.

    *It sounds like you have too rich an idle jet
  9. HeadSmess

    HeadSmess Well-Known Member

    the walbro are a far easier carb to use and adjust. whilst genuine keihins (and mikunis) have plenty of alternative jets and needles, the clones are always suspect regards needle tapers, lengths, sizes of needle jets, etc etc. and finding proper matches can be a nightmare. noone wants to help once they discover you have a non-genuine clone carb.

    a lathe would help, but trying to machine something as accurate as a needle is bordering on the impossible without some pretty dedicated tooling. steady rests, etc. i believe theyre normally ground on a centreless grinder designed specifically for the job at hand...grinding tapers. all they have to do is set the grinder up. all you have to do, on the other hand, is try to turn a varying taper to micron tolerances and know exactly how much taper is required at each point along the needle... ouch. sure, you can turn the taper with a tool, but then you have to polish out the marks left in it, and simply doing that changes everything. no point trying to modify an existing needles, as all you can do is remove material rather than add it...

    back to the walbros. its pretty easy to drill into the crankcase and fit a nipple for a pulse line.

    in my experience, most (not all of them)chainsaw carbs have the diaphgram cover plate fitted with a nipple, whereas most brushcutter/hedge trimmer types use an internal pulse line feeding through the intake manifold. its a pretty simple matter to block off the internal pulse line and simply drill and tap for a nipple in the cover plate. tear them apart and you soon see that the pulse line in either case works in exactly the same area, and some of the internal types even have the marks on the covers that coincide with the nipples as used on the external types...

    it is possible to try and drill the pulse line into the cylinder itself and use a standard (walbro) manifold, but just fitting a pulse line is far easier. remember to use some type of insulator between carb and engine, there is a reason all walbro carbs are fitted on those "plastic" manifolds. a nylon adaptor plate between carb and (steel)manifold, some aluminium and a nrubber hose,whatever, as long as the carb body is insulated from the engine itself.

    best nipples are the tiny ones used on nitro RC fuel systems... you arent after flow, just a pulse.

    use the butterfly type carbs, the rotary barrel ones usually do not have adjustable lo jets(some do). and while the shindaiwa brushcutters tend to use slide carbs, i havent seen any other size yet... though i have butterfly walbros ranging from 10mm to 24mm.

    engines that run "zama" carbs usually have carb issues. i dont like zama carbs.
  10. Steve Best

    Steve Best Well-Known Member

    Great post Headsmess.
    I alter my needles by either chucking them in the drill press (don't have a lathe) and emery paper them or I file a flat on them.
  11. HeadSmess

    HeadSmess Well-Known Member

    thats what i was getting at... all you can do is reduce their size, or make them "richer". if you need leaner, its a matter of yes..raising the clip, but also with the emery paper...theres no real accuracy, its just guesswork and experience at play. unless you can make them yourself but that is a huge job for what appears to be a dead simple and basic item.

    whereas real keihin and mikuni needles come in a huge variety of sizes, with different tapers at different points.


    just a small selection...note the diameters are in thousandths of a millimeter!

    theres no guarantee with a clone carb that the needle will even be at the same height when placed in two different(but identical) slides! simply because on slide may be marginally deeper than the other where the e-clip sits.

    which can be a pain in the rear if you want to fiddle around with adjusting the slides cutaway and decide you overdid it and want to go back to stock. the cutaway works in reverse to the needle though. increasing cutaway makes it leaner. very easy to go too far, very hard to return to stock.
  12. crazy mike

    crazy mike New Member

    ben burnin shell super in these things for years know problem
  13. Bill Busick

    Bill Busick Guest

    I have that set up I bought mine from it's the GT80 set up only thing is mine didn't come with a spacer for the reed valve box intake.the top screw is an idle screw and it starts having a effect at around 3 turns out. The only problem I ever had with mine was with the filter. I drove it it the rain one time and since then it ran like sh*t. At an idle it would run perfectly rev up high and everything but under a load couldn't go over to when before I was getting up to 55mph without redlining it. The problem was the filter held moisture and was to dense for air to pass through properly even though I could blow through it no problem. I took it off while riding it one day while it was raining because I was just getting pissed on how it was running. Let's face it I spent an ass of money on that setup and all the other performance upgrades to compliment it and it running that way while the stock by carb running better was unacceptable to me. Now she's running perfectly. And to answer a question earlier yes also sells a nice jet kit that comes with like 11 different slow jets ranging from.30 to .40mm and main jets from .70 to .90mm and also the main jet holder all that for a cheap $25. They also have a whole bunch of performance parts CNC racing parts and everything check it out