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Project FZR fix up

Discussion in 'Your 250cc Projects' started by Yetiburger, Oct 7, 2017.

  1. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    142psi sound's low to me, it might be the minimum acceptable psi
    I would have thought a new/fresh engine would be around 240psi ?
     
    Last edited: Sep 27, 2018
  2. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Static compression is only good for comparing across the same engines. The more overlap the lower the result, relatively speaking.
     
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  3. Andych

    Andych Senior Member Premium Member

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    I agree, I would have thought around 180 wet would be ok for a used engine.
    Plus they all need to be within 5 to 10% of each other.
    If you are doing it with the carbies on you will need someone to hold the throttle wide open.
    Test them all dry first, then with a squirt or 2 of oil down the bore.
    Personally I would always like to use the screw in adapters.
    You can also do a leak down test which would give you more info.


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  4. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Yeah throttle wide open and all 4 slide's wide open too.
    Just looked at the service manual on Compression Pressure and it say's Typical Pressure is 10kg/cm2 at 400rpm, so 142psi is right
    And Use Limit's is 8kg/cm2 at 400rpm, so 113psi
     
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  5. Andych

    Andych Senior Member Premium Member

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    Hmm I thought it would be higher. Isn’t the FZR a reasonably high compression engine?
    Doesn’t really matter though.
    Document the pressures and if something doesn’t add up. Re-test it, especially if you are just holding the tester down.
    I used to have a couple of adapters that would suit different spark plug dimensions but I seem to have lost them over the years.


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  6. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Yeah 12/1 compression

    3LN3 cam spec's

    20180927_120532.jpg
     
  7. Yetiburger

    Yetiburger Well-Known Member Premium Member

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    I did find this. would seem that the psi should be closer to 208 PSI
     

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  8. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    I guess just test it first, then again will a teaspoon/tablespoon of oil down each cylinder, if there's a big difference in compression it's most likely the ring's and or worn piston's, if it's close to the original result's then it's the valve's that need reseating or replacing if really worn.

    My guess at 240psi was a comparison to my Ford 351C (11/1 compression ratio) which had over 210psi when tested.
     
  9. Andych

    Andych Senior Member Premium Member

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    I would base any decisions on what to do with the motor around the Factory figures, while that document may be right in the general scheme of things the factory figures take into account the cam specs, piston clearances etc.
    Stick to 142PSI as a guide.. you want them all to be as close to that figure as possible
     
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  10. Bryn duFresne-Mann

    Bryn duFresne-Mann Active Member

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    With a 12:1 compression the theory would follow that 12x14.7= 176.4psi as a max so any more than 10% less would show an issue. so at 142 psi you're 20psi less that what I'd like to see- sounds about right for lowest tolerance.
     
  11. Andych

    Andych Senior Member Premium Member

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    You are not taking valve overlap into the equation as well as any leakage past the rings etc.
    An internal combustion engine is far from being 100% efficient.. in fact the latest versions of F1 engines are only now passing 50% Thermal efficiency.

    If you read the specs listed above by @my67xr where the factory says.. 142 psi (dependant on your altitude if you want to be really fussy).
    The theoretical pressure at 12:1 ratio has nothing at all to do with what will actually show on the gauge.
    Yours could show 138 psi across all 4 which would be extremely good.. but based on your theoretical limit at 12:1 would see you scraping the engine when it really would be in good condition..
    All tests should be done in conjunction with FACTORY Specifications.. nothing else.
     
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  12. Yetiburger

    Yetiburger Well-Known Member Premium Member

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    ok so i warm my bike up. it runs like ****. see a leek below the sump. once i can i give it a rev, boat loads of white smoke out the exhaust. turn it off. smell the leak, smells like gas. check the oil level, looks over full. i look for the leak and it looks as if its coming from the damn rocker cover. I had the fuel tap off and i fulled the tank when i took it out last. when i check the tank there is definitely a couple of liters missing. which im guessing is now in my oil. does this mean my floats are not closing properly and my fuel tap is stuffed? is my fresh oil in the bike now stuffed and needs to be replaced?
     
  13. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Yeah sound's like the needle and seats are leaking.
    Might be able to get away with just replacing the o ring around the seat's?
    Did you replace the needle and seat's before, i can't remember?
    Make sure the tip's of the needle's are still soft, with no groove's too
    I personally would bin the oil, you might be able to drain it into a tub and let the fuel evaporate but i'm not sure if i'd use it in the FZR again.
     
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  14. Yetiburger

    Yetiburger Well-Known Member Premium Member

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    yeah i replaced every part i could in the carbs. what could be done about the tap? don't see much point in doing a compression test until i sort this.
     
  15. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    Have u replaced the float needles?
    Have u done the seals in the fuel tap?

    Pull off the carbs and u should see fuel in the cylinder

    Drain the oil into a clean open container and let the fuel evaporate

    Take out the plugs and push the bike in gear forward a little to push out any excess fuel then let it sit for a few days with everything off to fully evaporate ... while u fix the problems

    https://litetek.co/Fuel_Tank_O-Rings_Yamaha.html
     
  16. Yetiburger

    Yetiburger Well-Known Member Premium Member

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    I have replaced the float needles. think i still need an oring for the tap.
     
  17. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    Even if the fuel tap is left open the floats should still shut off the fuel

    Might need to check the float needle seat is in place properly ... do they have new o rings?

    BDST_FloatAssembly_Fitted.jpg
     
    Last edited: Sep 29, 2018
  18. Yetiburger

    Yetiburger Well-Known Member Premium Member

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    yip new o rings from litetek. drained nearly 4 liters of oil. lots of gas around the carbs.
     
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  19. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Check the float levels and when you do so turn the ignition on so that the pump cycles. You might be able to determine which carb is flooding.
     
  20. Yetiburger

    Yetiburger Well-Known Member Premium Member

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    all the floats seem pretty sealed in the housing and the valves seem to all be working. maybe i got over zealous with one of the float levels?
     

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