Hi I have a 2002 mach Z with the PTO plug running lean.
I would like to do a leak test to see if I have a leaking seal etc.
However the service manual is confusing it saya to test each cyclinder individually then goes on to describe blocking off all the cyclinders (of a twin) at once. I blocked off the PTO cyclinder (RAVE,Exhaust,resinator and carb boot) but when I try to pressurise I hear air coming out the MAG carb !!.
Well, there are two leak type tests that you can preform on your engine. One is called a "Cyl. Leakage Test". This test is real easy but you will need an air compressor. Just go and buy a Cyl. Leakdown Tester from an auto parts store and follow the directions. This test checks the condition of the piston rings and head gaskets. The second test is an "Engine Pressure Test". This is the one that I think you are refering to becase you mentioned a "leaking seal". This test is more difficult but will test your eng. for air leaks. You will have to buy an Eng. Pressure Testing kit. How this works is you remove the carbs and insert plugs into the carb boots. Next you will have to remove the exh. system and plug the cyl. exh. ports and fuel pump implus fitting on the crankcase. If the eng. has exh. valves you will have to remove them and plug the valve openings. You will also have to plug the exh. valve oil drains. Just put a piece of gasline hose between them. Next you have to install one spark plug in one cyl. and the pressure gauge in the other spark plug hole. Rotate the eng. so both pistons are at the same height. Useing a hand pump (you can use an air compressor but you must be very careful) pump air into the eng. until the pressure gauge reads (8) psi. If your eng. is tight it should not leak more then (1)# in (1) minute. If it dose you will have to find the leak using soap and water with a brush and look for the bubbles. You can also submerge the eng. under water like an inner tube. Thats the prefered method. There is another test that can be done and that test is a vacuum test but thats another story.
See if your local mechanic or rental shop has a smoke machine that you could beg borrow or steal,this is what we have for pressurizing crankcases or anything else for that matter,works very well for checking seals,just make sure it is a low pressure unit.If the seal leaks you will see smoke come out,also can see it going from clyinder to clyinder or into cooling system.