Kinsler_Handbook_#32 December 2017

198 Kinsler Fuel Injection, Inc, 1834 THUNDERBIRD TROY, MICHIGAN 48084 U.S.A. www.Kinsler.com Phone (248) 362-1145 Fax (248) 362-1032 SPECIFIC GRAVITY 1) Holding the glass cylinder almost horizontal, place the hydrometer and thermometer into it. Slowly bring the cylinder to an upright position while jiggling them gently to the bottom. 2) Fill the cylinder to within an inch of the top with a sample of the gasoline. This will cause the hydrometer to project out of the top for easy positioning with your fingers. 3) Place the cylinder in the shade. Wait a few minutes for the temperature to stabilize. 4) Carefully sight across the bottom of the meniscus and read the hydrometer. It must be floating freely when you read it; not in contact with the cylinder or your fingers. 5) Hold the thermometer up so that it’s bulb is about at the the middle of the hydrometer’s bulb. Read the temperature. 6) Note that you now have the observed specific gravity. To find the true specific gravity you must go to the correction chart, go down the column that has the heading temperature that is closest to the one you observed, until you come to the specific gravity you observed, then go across to the 60 0 F column and read true specific gravity. PROCEDURE FOR OBTAINING OBSERVED SPECIFIC GRAVITY PROCEDURE FOR DETERMINING JET CHANGES FOR A CHANGE IN SPECIFIC GRAVITY CAUTION To avoid damage, always lower the hydrometer slowly into the liquid; dropping it may make it hit the bottom of the glass cylinder. Thermometer Hydrometer Meniscus Eye Since the specific gravity of a liquid decreases with a rise in it’s temperature, specific gravity must always be referenced to a particular temperature. The accepted standard is 60 0 F. However, since it is not convenient to have to measure the liquid at 60 0 F in the field, a chart has been made up to allow the specific gravity to be measured at any temperature, and then corrected to 60 0 F. Example : at 90 0 F, the specific gravity of a gasoline sample is found to be .747. Go to the chart and go down the column labeled 90 0 F until you find .747 . Now read the true specific gravity in the 60 0 F column as .760. In the procedure below, any time we refer to specific gravity, we mean corrected specific gravity... the specific gravity at 60 0 F. Procedure - To go from one type or batch of gasoline to a new one : 1) Measure the specific gravity of the “old” fuel, and note the jet size that worked best. 2) Measure the specific gravity of the “new” fuel. 3) Calculate the percent difference between the old fuel and the new one: New fuel specific gravity - Old fuel specific gravity Old fuel specific gravity EXAMPLE : A new fuel is checked as .712, old fuel is .736 .712 - .736 -.024 .736 .736 4) To make jetting correction : a) For fuel injectors... Using the table below, go up or down on jet size to get the same total % change as determined in step #3 above. Since the example was “-”, go to a richer (smaller) main jet. If it had been “+”, go to a leaner (larger) main jet. Percent change in fuel delivery to engine versus jet change for popular type fuel injection units, gasoline only : Engine Displacement Pump Size K-type Jet .002” K-type jet .004” Commercial Jet .005” 302 - 402 cid -0 3.0 6.0 7.5 402 - 520 cid -1 1.8 3.6 4.5 All size blown -1 1.8 3.6 4.5 b) For carburetors... Calculate the area of the old main jets and increase or decrease them by the same percentage found in step #3 above. Going larger on carburetor jets is richer. [ Old jet area = (old jet area X % from step #3) ] = new jet area Sign (+ or -) is the opposite of the sign found for the % in step #3. = = -.0326 = -3.26% © 2017

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