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Ron, To time the 172, here's what you need to do: 1. Verify #1 piston is on compression stroke. Only way I know is to pull valve cover and watch intake valve opening and then closing as piston is on the upstroke. 2. Using timing window, look for numbers on flywheel. Depending on your pump number, the injection timing will either occur at 18 or 23 degrees BTDC. If the last digit on the pump is a D or a J it's 23 degrees or if the last digit is a B or no letter, then it's 18 degrees. 3. Once you roll the engine over to get it at the correct flywheel position (and #1 on compression stroke), now look at timing window on the side of pump. There are two marks that should be lined up if the timing is correct. If they are not lined up then the mounting bolts on the pump must be loosened and the pump rotated a little in either direction. The pump can't move much as the fuel lines pretty much lock it in position. 4. Once these marks line up then the pump is properly timed. Now you have to bleed the system, starting with the fuel filter and then the bleed nut on the side of the pump. At this point you can also crack the injector lines (nuts) and spin the engine over until a good fuel spraying is seen/heard. Use a good hot battery so it spins over fast. If you're only getting a dripping/seaping or otherwise not getting a good "spitting" as the engine is spinning over, then the pump is defective and needs to be rebuilt--cost about $400-$650 or so depending on who does it and what all is needed. Now all this assumes you have a clean filter, clean fuel and no restrictions in the line from the tank. Oh, I forgot to mention one other thing--when you dropped the pump back into the drive hub, the larger side of the coupling should be facing the engine when the engine is in the #1 timed position. If you didn't pull the drive hub, then this shouldn't be a problem. If you pulled the drive hub, then we'll need some more steps....
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