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Thread: premix question

  1. #1

    premix question

    Just converted GP760 to premix, but it has nearly a full tank of gas. If I add oil to the gas, how long will it take to mix (or will it)? Should I drain some fo the gas out and add oil then add the reminaing gas to mix it.


  2. #2

    Join Date
    Jan 2006
    Texas City, Texas
    The real issue is to get the appropriate amount of oil to mix with the known amount of gas.

    If you do not know how much gas that you have you can either

    1. Drain it all and determine the amount of gas that you have and then mix to the ratio that you want to run.

    2. Find out how much the 760 fuel tank can hold (you can use your manual for this). Once you determine that, then you can drain at least 5 gallons of the fuel, mix all of the oil that is required for the full tank into that 5 gallons. You would then dump the premixed oil back into the tank. Top the tank off with fresh fuel to get the appropriate oil to gas mixture. Adding the extra fuel would not only help you to get the proper ratio, but would also help you to mix what ever is in the tank a tad better. This is a bit of work, but you should do all that you can to mix the oil and fuel as best as you can. Sloshing it around the tank while you are ideling around in the water for the first few minutes should more than complete the mixing.

    This is how I would do it if it were my boat.

  3. #3
    rabzman's Avatar
    Join Date
    Aug 2008
    Eastpointe, MI

    says 40 litres = 10.6 gallons

    So fill the tank all the way up and add your oil. You could round up to 11 or 12 gallons and add enough oil for whatever ratio your trying to achieve.

    10.6 gallons fuel, add 27.2 oz oil
    11 gallons, add 28.2 oz
    12 gallons, add 30.7 oz

    10.6 gallons fuel, add 33.9 oz oil
    11 gallons, add 35.2 oz
    12 gallons, add 38.4 oz

    Whew, thats the scientific way to do it. However, you could just fill the tank and add the 35 oz oil and get @40:1.

    But if the gas is old, last season crap, then drain the tank and use that on a bonfire and start with nice freshies!

  4. #4
    I wanna go FAAAAASTer!! CDW78's Avatar
    Join Date
    Mar 2010
    The other gp1200 I just got had a new top end installed days before I picked it up. The guy said mix 50:1 till it was empty on the first tank.....
    Whats the exact amount of oil @ 50:1 in these gp's ( 13.2 Gal. tank, correct ? )

    Should I keep this ratio for a while ?

    And over all - whats a good rule to run this as permanently ?

    Thanks in advance - I'd prefer to baby it and not take a single chance

    AND while I'm at it, 87 octane the best for these 1200's ?

  5. #5
    rabzman's Avatar
    Join Date
    Aug 2008
    Eastpointe, MI
    The math is:

    1 gal = 128 fl oz

    (# gallons x 128 )
    ---------------- = oz oil to add

    (13.2 x 128 ) / 50 = 33.8 oz oil

    Note that after having added oil to a full tank you will only be mixing oil to the amount of gas added. Do yourself a favor and get a "ratio rite" mixing cup. I prefere the "maxima" oil one as it has a screw on lid, and it fits in most all storage compartments, even fire extingusher storage on stand ups.

    Most everyone runs a pre mix 40:1 mixtue. The big question is do you still have oil injection on your 1200???? If so you would only want to add oil to the gas tank at a 100:1 ratio for break in only and then keep filling your oil tank and let the oil pump do the work. But if your strictly a premix ski, I would run 40:1 all the time, even during break in. However, most people have differing opinions on this subject. You may want to follow your mechanics advice to a T. Especially if he gave you a warranty.

    As far as the octane goes, 87 is fine for a completely stock, un-molested machine, un-modified machine. But you said the top end was redone. You might want to see how much compression each cylinder has before running 87. If it seems high then you'll want to check the squish to see if it's within stock tolerances. Sometimes shops use cheapie base gaskets that are thinner that the stock ones that the motor was built with which raises the compression. While this slight raise in compression will make your 1200 fell snappier on the bottom, too much compression increase will mandate that you go higher on the octane. If this is the case then toss all rules of thumb out the window as there are too many unknowns.

    Another question you should ask your mechanic is "what caused the top end failure", and did he fix it? All to many times I hear of people taking their pwc back to the dealer for a top end repair only to blow it up right when they get back out on the lake. Stock top end failues are usually do to either detonation (ignition timing), lean condition (clogged mikuni filters or bad fuel pump or case/air leak), bad gas (old, or water contamination), or a combination of all three.

    I know this is a long winded response, but I hope this helps.
    Last edited by rabzman; 05-04-2010 at 09:06 AM. Reason: smilies in place of 8's

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