Carby Keihin carb clone

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

  1. SRPM

    SRPM Member

    Ok now I have drilled down to a #76 bit from a #74 bit on my main jet and lost power, it's a bit colder than it has been too. I didn't go more then 2 blocks in fear of damaging the engine. Here's the plug after the sort run, doesn't do much good with such a short ride but maybe it'll help. Plug is a NGK B7HS 20160511_181335.jpg
     

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  2. SRPM

    SRPM Member

    Also have noticed my leak has returned so it might be sucking air through it.
     
  3. Steve Best

    Steve Best Well-Known Member

    No, I disagree. No need for high octane race fuel with these motors unless you have some sort of a rocket science racing rig. If you do, you know enough not to ask the question. If you have to ask the question, you don't need high octane. Make sense?

    SRPM, we cannot see deep enough down into the plug to see the smoke ring. You did the right thing, staying on the side of caution. You are looking for a brown smoke ring down inside that electrode insulator. The cold also makes it run lean.
     
    Last edited: May 11, 2016
  4. butre

    butre Well-Known Member

    if it didn't say no ethanol then it has ethanol.

    use this website to find ethanol-free gas in your area

    http://www.pure-gas.org/
     
    Neptunati and SRPM like this.
  5. Neptunati

    Neptunati New Member

    I think the only time you need higher octane fuel is if you pinging or detonating, right? But boy me loves the smell of some turbo blue race gas! They still sell it?
     
  6. Hey so does anyone happen to know the float height for this i messured im getting about 20 mm and i think thats wrong but im not sure
     

    Attached Files:

    Last edited: May 13, 2016
  7. HeadSmess

    HeadSmess Well-Known Member

    dont measure. stick clear hose on bowl drain, loosen drain screw, hold hose against side of carb...adjust float until fuel is 1-2mm below bowl gasket. simple.
     
  8. 45u

    45u Active Member

    Do these carbs have a low speed adjusting screw? With a reed valve if you want to get the most out of it you need to window the piston.
     
  9. Batman6583

    Batman6583 New Member

    Hello let me share my experience with this clone let's start by saying I'm at sea level in Sunny South Florida my back is equipped with a high compression head and expansion chamber and high performance CDI and a port and polish cylinder with the transfer port. I have try 110 octane fuel and 92 octane fuel, I have try the stock spark plug and the NGK spark plug, I have try an piston with no hole and a piston with a hole in the side I have try 32 tooth sprocket and 36 tooth sprocket. The motor run very well, low end power is very good the bike cruise very well at 38 miles per hour with an 36 tooth sprocket, I haven't really tried to top it out because it's still in the break-in period I got about a total of 125 miles on the back so far and the fuel ratio is 25 - 1 the Clone really made an improvement in the performance of my bike. I reposition the needle for a richer mix, I find tuna just met with the air and fuel mixture screw, the idle screw never showed any type of affect. I used throttle cable adjustment to adjust the idle speed, maybe I just been lucky
     
  10. 45u

    45u Active Member

    I am going with a Mikuni VM Series Round Slide Carburetor 18MM Clamp Mount | VM18-144-WP. It is fully adjustable even has a low speed adjustment. If you have to use the throttle cable to adjust the idle speed something is not correct.

    Seems know on know is if it has adjustable low speed or not as I have asked.
     
  11. Batman6583

    Batman6583 New Member

    I know you're right. Maybe after break in. I'll try to fine tune it better.
    And what I meant was I use the fuel and air mixture screw two fine tune the Carburetor. Lots of luck with your new carburetor Cheers
     
  12. Batman6583

    Batman6583 New Member

    You know auto Corrections really suck
     
  13. 45u

    45u Active Member


    So this calibrator has a low speed adjustment??????????? Not the idle but low speed adjustment?
     
  14. Batman6583

    Batman6583 New Member

  15. Made

    Made Guest

    Can I run this motor without the velocity stack and reed value my reed values went bad and now can't get motor to run right
     
  16. Batman6583

    Batman6583 New Member

    It's not going to work right without an Reed valve because the GT80 cylinder has a third transfer port
     
    SRPM likes this.
  17. jaguar

    jaguar Well-Known Member

    Steve, I know you don't make things up but I heard quite different from what you said about 32:1 being the maximum amount of oil to use.
    Here are my guidelines with the belief that more is better protection without interference of ignition:
    standard mineral oil 20:1
    semi-synthetic 25:1
    full synthetic 30:1
     
  18. Steve Best

    Steve Best Well-Known Member

    Gordon Jenning wrote a ground breaking article back in the late 70s about oil mixture:
    http://www.bridgestonemotorcycle.com/documents/oilpremix6.pdf

    We followed this like a religion back then in the era of cast iron sleeves and before power valves.
    This information is accurate for castor oil, which was the go to back then for maximum scuff resistance.
    The 50:1 oils back then were only designed for low powered engines, fouling resistance and smoke resistance.
    I ran a CR250 and a 340TNT sled and didn't go anywhere without a pocket full of plugs and a wrench.

    In 2000 I bought a KTM 125EXC that called for synthetic oil at 40:1.
    Since I still kept a spare plug and wrench, I ran that plug for YEARS, before it fouled.
    Wow. Since then I have switched to 50:1 and usually run Motul or Ipone. After 7 years of use the head looked like new.
    The synthetic stays fluid and doesn't soot up and stick, which is why it is used for powervalve engines. It is self cleaning.
    7 years and my nikasil cylinder and piston was still in amazing shape, no scuffing, little wear.
    I did try other oils in the KTM and found oil is an important component of low rpm ring sealing and cheap oils (and injector oils) don't cut it. Top of the line synthetic pre-mix oils are the only ones that deliver ring sealing and foul resistance.

    These engines are different. Thin chrome bore. Where to start? I followed the manufacturer's recommendation. 16:1
    What a mess! Oil dripping out of the pipe, hard starting and very soon fouled plug. No surprise, even at 20:1.
    I gradually thinned the oil (and wrote about it on these forums). 40:1 gave a noticeable lack of low speed ring sealing so I settled on 32:1. Bike performs the same as on 24:1 without the oil dripping from the pipe. I have been jumping around with synthetic, semi-syn and conventional oils, using up the various gallons we have in the shop and seeing what the results are for performance and carboning. All seem to work better at 32:1 than 40:1, even the synthetic, probably due to loose tolerances.

    Here is the latest look at the head off with an unknown 32:1 semi-synthetic (was put in an Ipone measure bottle years ago) I am using up:
    [​IMG]

    It is a soft sticky wet soot. It wiped off the polished sections well, but not the cast areas:
    [​IMG]

    It has been hard breaking the mould of what I think I know and what I have read and believed for many years. That is why I am testing all I can again with these engines, to challenge what I think I know, is it true?

    Steve
     
  19. jaguar

    jaguar Well-Known Member

    well we are in agreement about ratio for synthetic oil but not about regular mineral oil
     
  20. jaguar

    jaguar Well-Known Member

    Steve:
    Jennings, in that paper, said that 16:1 gave the best power and protection. I think you quoted the wrong paper to back up your belief.
     
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