Hi Shifty. First, the simplest one. The recommended spark plug is a CJ8 or equivalent. This is the usual spark plug for most mowers, leaf blowers, line trimmers, etc. It is almost universal.
Before we get seriously into your engine tune-up, please post the full string of numbers stamped on the air cowl. These are in three blocks. We need that information in this thread so it will make sense in the archives.
Your intake pipe popping problem is probably due to either lean mixture or a leaky intake valve. There is more than one possible cause of either of these problems, so we need to collect some basic diagnostic information.
I suggest you go through a proper diagnostic procedure, since your 60102 is new to you, and we therefore don't know its history. Look in the fuel tank for any signs of debris (sediment, grass etc.) If there are any such signs, it will need to be cleaned out - we can talk about how to do that if it is needed. Check that the spark is adequate - remove spark plug, hold plug lead about 3 mm from the cylinder head or cylinder, pull starter, and watch for a steady series of blue sparks. Reinstall spark plug but don't connect the plug lead, and pull the starter a few times to get the feel of the compression. Then remove spark plug, put a spoonful of engine oil in through the plug hole, reinstall the plug without the plug lead, and pull the starter a few more times. Is the compression resistance noticeably greater with the oil in there? If so, your piston rings are leaking and need to be replaced. Check that the governor is working: vary the speed control, which might be either a lever control, or a pull-push wire on top of the carburetor. Does the engine speed increase and decrease through a sensible range when you do this? If it seems to be going way too fast at any time, shut it down and we can do some diagnostics on the governor. (Of course there will be quite a lot of blue smoke when you fire it up after putting the oil into the cylinder: don't worry about it, the smoke will stop after a couple of minutes when all the oil is burned up.)
Having done all that, we should have enough information to move on to specific diagnoses. If you found debris in the fuel tank, we can't yet do the first diagnostic thing, which is to look at the mixture. If the tank is clean, run the engine at maximum governed speed, and use a screwdriver to adjust the mixture screw, which sticks out from the side of the carburetor and has a spring under its head. Turn it clockwise in small increments until the engine slows down a bit or you notice the throttle butterfly lever on top of the carburetor starting to move back and forth. This is the lean limit: it indicates the engine is now running too lean. Then turn the mixture screw anticlockwise in small increments until the engine slows down a bit. That is the rich limit. The correct mixture is halfway between the lean and rich limits. If this mixture adjustment procedure goes smoothly and gives a fairly clear answer, you have probably found the problem, and fixed it.
Next step is to measure the tappet clearances. To do that, remove the valve chest cover, held by 2 screws on the side of the cylinder, between the carburetor/muffler, and the crankcase. The valve chest cover is also the crankcase ventilation valve. When you have removed it you will see the valve springs behind it. At one end of each spring, the tappet pushes the valve up and down as the engine rotates. Rotate the engine until it is just a smidgeon (technical term) past top dead center on the compression stroke. At that point there will be clearance between each tappet and the end of the valve stem. Use feeler gauges slipped into the clearance gap to measure how much clearance there is. The required amount is 0.005-0.007" for the intake valve, and 0.009-0.011" for the exhaust valve. If clearance is outside this range, it will need to be adjusted. There is no way clearance can be reduced if it is excessive, except by replacing the valve (because its stem is too short). If there is not enough clearance, it is increased by removing the valve and grinding away the end of the stem. However, you never attempt to adjust clearance without first lapping the valve into its seat, because the clearance will change when you lap it. We can talk about how to lap the valves if you find the clearance is incorrect.
Note that it is possible you will find that the mixture adjustment does not really work properly because the engine gives symptoms of lean mixture even when the screw is turned a long way anticlockwise. If this happens it means the carburetor will have to be cleaned and inspected. Again, we can talk about how to do that if the results show it is necessary.
Please post results for this process and we can talk about next steps. If you aren't clear on something, let's talk about it until it is clear - you aren't likely to get useful results by working in the dark.
