Recent content by John Murray

  1. John Murray

    Ton up SR250: 100mph, 100kg, 30hp

    I doubt you'll need a pump for such a small volume of fuel. Most motorcycle carbs can only hold back a very low level of pump pressure (like 1.5psi or less) before the needle is overcome and the bowl overflows. It's generally more productive to use a larger bore seat without a pump and check...
  2. John Murray

    Ton up SR250: 100mph, 100kg, 30hp

    Great story and pics! Don't be disappointed, that's a very good result for a first outing. Fuel flow can be easily checked, and is best done by measuring the fuel flow over a minute. If at all possible you should include the float valve in the flow path by measuring the flow out of the bowl...
  3. John Murray

    My Bultacos

    Not really insane for a fairly recent engine - the water cooled engine uses a Rotax cylinder - it isn't even super highly tuned. To put it in perspective the Aprilia 125cc GP bikes made over 55hp, the 500s were around 200hp and the 250s were around 100hp. I miss two stroke GP racing. In street...
  4. John Murray

    Ton up SR250: 100mph, 100kg, 30hp

    Sounds like quite a successful session. I think you have enough hp to crack 100mph. Team Afflick over here holds quite a few records in smaller classes, mainly 100cc. Here's what he once wrote "To go 100mph without a fairing you will need 23-25 rear wheel HP. We ran 94.5mph with 21hp and then...
  5. John Murray

    My Bultacos

    In street trim with the air cooled 370 it made low to mid 50s. In LSR trim with water-cooled 350 it makes 75 to 80 odd.
  6. John Murray

    Ton up SR250: 100mph, 100kg, 30hp

    APSF-350. It's a 350cc single. Record is at only 128mph, but best speed unofficially is 155mph. Hope to get at least into the 160s.
  7. John Murray

    Ton up SR250: 100mph, 100kg, 30hp

    Yes, the prime position bypasses the vacuum control and allows fuel flow without vacuum.
  8. John Murray

    Ton up SR250: 100mph, 100kg, 30hp

    I'm really enjoying this thread - lightweight, skinny bikes have always appealed to me. I've been land speed racing at Lake Gairdner (Australia) for the last few years - class record holder - and suspect you'll have no trouble cracking the ton. I think you'll need more than a half mile runway...
  9. John Murray

    Texas Two Step Taco

    Assuming you're gonna run gas thru the low speed circuit (and I think it's worth doing) remove the line and fittings from the bowl to the front (engine side) hose tail and plug the bowl. The small gas tank should be mounted as close as possible to the carb, and the fuel level when the tank is...
  10. John Murray

    Texas Two Step Taco

    You don't. And can't to any useful degree. Tune by the torque gauge and the timeslip. A nice thing about two strokes is they give very clear indications of A/F by the sound and feel, not so much with alky but they're still there. I haven't read a plug in decades.
  11. John Murray

    Texas Two Step Taco

    A naturally aspirated engine on alky shouldn't be melting plugs at all, and if it is it would indicate something grossly mis-configured.
  12. John Murray

    Texas Two Step Taco

    Yes, but not just Kevlar briefs :eek: Don't get too excited by the spark plug; it won't make you any more power. They do seem to last a very long time though - I've been using the same one for years.
  13. John Murray

    Texas Two Step Taco

    What I meant was a sufficiently powerful ignition system will fire a surface gap plug in the grease bucket. An inductive ignition won't do it and many motorcycle CDs won't either. If you're gonna run a surface gap make sure you have an ignition that can fire it consistently. Mercury Marine...
  14. John Murray

    Texas Two Step Taco

    It was so silly I'm almost too embarrassed to tell.. When I painted the tank I got some overspray inside it, near the filler neck. No problem I thought, the alky will just dissolve it and it will pass through the system. That was mistake number one. Number two was being so eager to get it on...
Top Bottom