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Project ZXR250A - The Wasp.

Discussion in 'Your 250cc Projects' started by Murdo, Aug 14, 2018.

  1. Andych

    Andych Well-Known Member Premium Member

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    Ohhhh SU huh, going “Old Skool”, I like it.
    Plenty of tuning options and sizes around and then if you still have trouble there are side draft Strombergs you can play with.

    But I think @Murdo will be all over an SU setup like a fat kid in a Lolly shop


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  2. Murdo

    Murdo The Good Doctor Staff Member Premium Member Ride and Events Crew Contributing Member

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    'Fat kid in a lollie shop'? Who you looking at? :lolsign:
     
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  3. Andych

    Andych Well-Known Member Premium Member

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    Well I was looking at my own reflection in the window at the time :)
     
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  4. Murdo

    Murdo The Good Doctor Staff Member Premium Member Ride and Events Crew Contributing Member

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    :lolsign::lolsign::lolsign:
    I do have a bit of experience with SU's. Most people don't take the time to understand them and curse at them. How hard can it be for a carb with 3 moving parts?
     
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  5. Andych

    Andych Well-Known Member Premium Member

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    Did you learn to synchronise them using a piece of garden hose held up to your ear... easiest way to go deaf... but once you knew what you were doing it was easy as pi$$
     
  6. Murdo

    Murdo The Good Doctor Staff Member Premium Member Ride and Events Crew Contributing Member

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    True, but I went up market and bought the proper manometer to synchronize them. Only need one 1 1/4" for this job.
     
  7. Andych

    Andych Well-Known Member Premium Member

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    Yes... should be ample considering twin 1.25" SU's managed to produce 75hp from the 1275cc Cooper S.. and while a sweet little engine the A series BMC was far from sophisticated or terribly efficient unlike the the ZXR250.
    There are also a big range of needles to ensure enough fuel can be dumped in.. well done @Murdo & @Frankster
     
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  8. Tigger996

    Tigger996 Active Member Premium Member Contributing Member

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    A single 2" SU will give you the same area/Airflow as four 26mm carbs.
     
  9. Murdo

    Murdo The Good Doctor Staff Member Premium Member Ride and Events Crew Contributing Member

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    That may be so Tigger, but the intake hole in the pump is only 1 1/4" and to fit a 2" carb would, I doubt, have enough airspeed to lift the slide fully and make needle selection and tuning nearly impossible. I have three 1 1/4" carbs and .... to tell any more would give away secrets. :D
    The worlds fastest Velocette uses a single 2" carb feeding a supercharger and nearly 600cc (although he has too small a fuel bowl and has gone about getting fuel to the carb a different way to what I would have) and it seems to go alright at 193+ mph.
     
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    Last edited: Dec 31, 2018
  10. Andych

    Andych Well-Known Member Premium Member

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    Oohhh its getting more interesting.. hmm as it is being designed to run on Salt (we assume :)) the power mostly needs to be top end only.. hence the basic log style ... so a reasonably large A/R will work well.. and I have no doubt @Murdo will have that all nicely sussed out..
     
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  11. Tigger996

    Tigger996 Active Member Premium Member Contributing Member

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    Having the 1 1/4 SU's is a very good reason for using them. Talking to Justin Newell (He has just rebuilt Little David) the other day and he is using a larger SU than you. Little David has a diet of very high percentage of nitro, so needs less air. A small carb with give you better torque low down, but the salt runs would be full bore. Have you considered a dual choke progressive Weber or using two 1 1/4's with the second one cutting in at half throttle and both fully open at full throttle(like the Weber).
     
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  12. Murdo

    Murdo The Good Doctor Staff Member Premium Member Ride and Events Crew Contributing Member

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    No room for downdraught DGV, DFV type (or even sidedraught DCOE), but I do have three SU's to play with. :D
    The use of a massive carb (compared to engine size) will not give the results we are looking for, so baby steps first. I've seen so many people shove bigger and bigger carbs onto engines trying to get more HP and only making their cars go slower. It's all about airspeed into and out of the pump. The SU (or any Constant Velocity carb) will keep the airspeed up by raising or lowering the slide unrelated to what the throttle plate is doing, but what the engine needs to make HP.
     
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  13. ShaneP

    ShaneP Well-Known Member Premium Member Contributing Member

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    If you want spare engine/parts, I have 2½ zxr250c motors?

    The zxr engine has barrels separate to the block, so the barrels can be lifted to reduce compression, rather than a head spacer or changing con-rods. Starting it could be tricky with low compression and valves closing so late into the compression stroke. In standard tune, the torque drops from about 10,500rpm, dropping faster after 14-15k. I do believe the ignition advances when going faster, but will you be advancing it further? Maybe a tuneable ignitor from these guys: http://www.ignitech.cz/en/ (I was also considering their efi system)?

    Good luck with your drag bike (and whatever else) project!
     
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  14. Frankster

    Frankster See the World before you leave it Staff Member Premium Member Ride and Events Crew

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    Thanks for the offer Shane, but we should be okay. Cheers Frank
     
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  15. Murdo

    Murdo The Good Doctor Staff Member Premium Member Ride and Events Crew Contributing Member

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    Maico 250, Royal Enfield 250, CF 250 V5 and 650TK, XL250, CBR250, ZZR250 plus a few others.
    A couple of bits arrived in the post.
    Oil cooler for the oil system.
    Salt bike turbo install 001.jpg
    Alloy tube and plate for the plenum chamber.
    Trimmed the ends to fit, drilled the manifold holes and roughly cut out the port holes to be finished later when bolted to head.
    Salt bike turbo install 004.jpg Salt bike turbo install 005.jpg Salt bike turbo install 007.jpg
    Made the mounts to hold the weight of the turbine and tacked up the pipes for trial fit.
    Salt bike turbo install 026.jpg Salt bike turbo install 019.jpg
    Am putting the pipe out the rear to use the hot exhaust gas to fill the vacuum created by the riders body, and reduce a bit of drag.
    Salt bike turbo install 021.jpg
    Still lots of trimming and welding to do yet.
     
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  16. Murdo

    Murdo The Good Doctor Staff Member Premium Member Ride and Events Crew Contributing Member

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    All welds done on the exhaust now. Need to have the TIG fixed to do the alloy.
    xxx 009.jpg
     
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  17. Murdo

    Murdo The Good Doctor Staff Member Premium Member Ride and Events Crew Contributing Member

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    The heatwrap I ordered arrived yesterday so got in and did a bit before it got too hot.
    I bought 15me and still didn't have enough.
    Heat wrap pipes 001.jpg
    Just to make sure it was fireproof I cut a bit off and hit it with oxy torch. Just went a bit brown.
    Heat wrap pipes 005.jpg
    Made gaskets from some old manifold material I had on hand.
    Heat wrap pipes 003.jpg Heat wrap pipes 008.jpg Heat wrap pipes 010.jpg Heat wrap pipes 007.jpg
    That should help keep the rider cool.
     
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  18. Murdo

    Murdo The Good Doctor Staff Member Premium Member Ride and Events Crew Contributing Member

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    Been getting out of bed in the 'Sparrow fart Dawn' and getting some work done before it gets too hot.
    Today I finished the welding of the fuel tank.
    Salt bike 005.jpg
    I pressure tested it with 30psi of air. Had two pin holes to reweld.
    Salt bike 007.jpg
    Cleaned up ready to go.
    Salt bike 012.jpg
    After that I welded the ends to the plenum chamber, cut out with plasma cutter, sanded smooth and drilled for the top plate.
    Salt bike 008.jpg
    I used a 3mm pilot drill, then one of these tricky drill and thread bits.
    Salt bike 010.jpg
    Cut some gaskets and ready to fit.
    Salt bike 011.jpg
     
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  19. GreyImport

    GreyImport Administrator Staff Member The Big Cheese Contributing Member

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    We need a 'fuking brilliant' button on the posts

    Ill have to drop in and check out these creations ... great work :D

    I think u guys are worried the "Flyer" is going to flog u :lolsign: ... if it ever runs that is
     
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  20. Murdo

    Murdo The Good Doctor Staff Member Premium Member Ride and Events Crew Contributing Member

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    Ready when you are. :D
     
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