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Help GSXR250 GJ72a correct spark plugs?

Discussion in 'Suzuki 250cc In-line 4's' started by buttersnips, Aug 13, 2020.

  1. buttersnips

    buttersnips Member

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    Hi
    i have recently acquired a gj72a gsxr250 and replaced the spark plugs yesterday, however now it is getting quite hot and quite fast compared to before. exactly the same plugs as before, CR7HSA. Old ones were pretty fouled (as in pitch black, i did move the clips on the needles on the carbs up a notch for a slightly leaner mixture but am i doing it wrong?) i think i read somewhere these are supposed to run CR9EK plugs?
     
  2. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    7's seem to be the middle of the range according to the manual. Mind you it is in Japanese so it would be good to translate it.
    Plugs_1.jpg Plugs_2.jpg Plugs_3.jpg
     
  3. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    As you said it is running the same plugs as before and you have lowered the needles to lean it off a little. If it is making more power then it will run hotter. Here is a good guide to reading spark plugs. http://www.crankshaftcoalition.com/wiki/Reading_spark_plugs
    Personally it sounds like you have made the correct move to me. Most of what you read on the internet about fitting bigger jets to make more power etc is just nonsense, in my humble opinion.
     
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    • Well said! Well said! x 1
  4. buttersnips

    buttersnips Member

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    Cheers for the reply.
    It was a short run so I don't know if it was just as it should be. Temp gauge wasn't in the red but getting close.. will try another test run tomorrow.
    Another issue I have is around 11k rpm (110-120kph) it just bogs down and wont pull any more than that. I'm suspecting the filter in the tank to be partly clogged so it's just starvation at high rpms, it's running fine below 11k and pulling fine as well
     
  5. DannoXYZ

    DannoXYZ Well-Known Member

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    Yes, most stock bikes are configured to be richer than optimal by manufacturers. This is for safety margin in case you run across bad petrol in middle of nowhere. Or encountre super-hot day.

    In '60s, there was hot-rod saying on how to make power...
     
  6. buttersnips

    buttersnips Member

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    Yeah, not gonna be a problem. I only run 100 octane since it has the least amoumt of ethanol mixed in - habit from running my old air cooled VW. According to some veedub forums higher octane has a colder combustion as well
     
  7. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Your cooling system might due for an overhaul.
     
  8. DannoXYZ

    DannoXYZ Well-Known Member

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  9. buttersnips

    buttersnips Member

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    What would this entail?

    Stupid question maybe, bear with me.. I am used to old aircooled Volkswagens :crazypilot:
     
  10. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Remove radiator & thermostat, clean and inspect. If it looks like a rusty mess then do the same with all of the hoses. Flush the radiator and replace or repair if it is blocked in any way.
     
  11. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    Your overflow bottle is probably full of sludge also

    overflow.png
     
  12. buttersnips

    buttersnips Member

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    Ouch. It is Indeed a rusty mess.
    Just taking off the cap reveals a bunch of rusty fluid.
    Does the carbs have built in fuel filters or should i just check the one in the tank?
     
  13. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    The parts book will show all of that information. Check inside the tank for rust and debris. If it look bad assume the worst. In fact I think the best way is just to assume that everything is bad and the only person that has ever worked on it since it left Japan is a chimpanzee with a brick and a cold chisel. Then if you find some things that aren't so bad it will be a pleasant surprise. Next stop will be brake fluid reservoirs to see if they still have the same fluid in them that the factory put in 30 years ago. At least you have a runner and that is a very good start.
     
  14. DannoXYZ

    DannoXYZ Well-Known Member

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    I automatically flush out cooling-system and replace thermostat when getting used bike.
    Also verify that thermo-switch is turning on FAN. Typically around 103-105C triggers fan-operation.
    Both thermostat and thermo-switch can be tested to verify if they're good or bad.
    Then you'll have useful information to determine if they were culprits behind overheating.

    In some cases, I've encountered clogged radiators, and water-pumps with worn fins.
     
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  15. buttersnips

    buttersnips Member

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    The fuel mixture screws on the top side of the carbs, how do they function exactly?
    Screwed in further = more fuel?
     
  16. DannoXYZ

    DannoXYZ Well-Known Member

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