The replacement Big Block V8 Engine was the 8.1L 496 Cu In motor which ran production through around 2010. Several different versions of the 7.4L and 8.2L engines were utilized throughout the years until 2002 when this engine family was discontinued by General Motors. However after the 1990's rolled around the 8.2L 502 Cu In Big Block V8 was introduced. Throughout the 1980's the 7.4L 454 Cu In Big Block V8 was the primary Big Block Inboard Marine Engine offered by Mercruiser. Mercruiser Big Block V8 Inboard (.Read More) Engines date back to the 482 Cu In motors offered in the late 1960's. Serial Number Entry: Search Diagrams by ModelĤ54 MAG. And by all means, remove that ?weird? fuel before contaminating the fuel system again.**ORIGINAL SEARCH TOOL** Search Mercruiser Big Block V8 Inboard Engine Serial Numbers You will still have to verify/adjust your compression, dwell angle, basic ignition timing, idle mixtures and idle speed. ONLY a waterborne test can confirm the elimination of the back fire condition. Lacking a full stream of fuel, there?s your main problem. ![]() You are looking for two healthy ?****? streams of fuel in the center of the venture. Have an assistant at the helm throttle to full ahead (engine OFF)while you observe the accelerator pump?s squirt nozzles in the throat of the carb. Secure the engine and remove the flame arrestor. Run the engine on muffs a few minutes to ensure that the carb is full of fresh fuel. I recommend you disconnect the main tank fuel supply line and temporarily connect an auxiliary, fresh/clean fuel supply in its place. When you say ? backfires? I am assuming you mean through the flame arrester.Ī backfire condition usually exists for one or more of just a few reasons, though each of those reasons may have several attributes.ġ) Lean fuel mixture: low fuel level, weak accelerator pump, vacuum leak, leaking valves,etc.Ģ) over-advanced ignition timing: high initial setting, stuck advance plate, vacuum leak, etc.ģ) random ignition firing: defective ignition wiring, defective distributor cap/rotor, etc.īased upon your initial descriptions of the backfiring condition, I would first suspect the accelerator pump in the carb. The corporate knowledge bank is full of wisdom. Thanks in advance for any help you can provide.įirst off: WELCOME to iBoats !!!!! It?s THE PLACE to be with boating questions. It might be awhile before I can try some of your suggestions as I do live in northern Ohio and everything is winterized and ready our "lovely" winters. I should note that when changing the fuel sending unit, the gas in the tank smelled very weird. If you shut the motor off after backfiring, it will start back up perfectly. ![]() I noticed that when opening the throttle fast, the boat would kind of hesitate before picking up then after running great for awhile then backing off for a minute and trying to opening it back up it backfires (does not stall out though). ![]() Things I have already done - replaced the spark plugs, distributor cap, points, rotor, fuel filter, fuel line, engine oil & filter (as well as 4" heat exchanger, new thermostat, anti-freeze, water pump assembly, seals and drive oil). I have a 1984 Mercruiser 470, 170hp, 3.7 litre with a Mercarb 2brl carb. I am new to owning a boat although I have pick up a lot of great info from this forum.
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