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Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10597
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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At idle, engine sounds great. Replaced distributor, cap,

Customer Question

At idle, engine sounds great. Replaced distributor, cap, ignition coil, wires and spark plugs due to engine misfiring and ultimately not starting. After replacement and proper adjustment (#1 at TDC) engine started and idled almost perfectly. Adjusted to advance slightly to get it near perfect. Took it out yesterday for test run, at 2000rpm it bogs down and pops like a misfire until I bring it below that then she runs great. I can clutch ahead all day with no issues. I have proper fuel flow into the carb, clean fuel. Just replaced filter and fuel line. Pulled carb and inspected for blockage, none found. I can properly choke out the engine by hand til it dies. It's almost as if the engine is in a protect mode, not sure if that's a thing.
Submitted: 5 months ago.
Category: Boat
Expert:  Tan replied 5 months ago.
Hello. My name is ***** ***** doesn't have a guardian mode as you have no computer. Bogging and popping are fuel starvation. Have you tried running the engine on a different fuel source?What do you have the timing set at?
Customer: replied 5 months ago.
The timing is set at 8degrees btdc.. Not sure what you mean by different fuel source, like an external tank? I've heard of theories involving clogged or blocked tank vents also.. Any experience?
Expert:  Tan replied 5 months ago.
Yes external fuel tank 5 gallon gas can and a piece of fuel hose connected to the fuel filter of the engine. Be sure to plug the fuel line you remove from the engine.Clogged vent is possible to c see if it is a vent just remove the fuel fill cap. But to completely eliminate the boat side fuel system run engine on another fuel source.What happens is over time you get debris in the fuel tank and if you use ethanol enriched fuels you will get a sludge build up in the tank. On the end of the pick up tube in the tank is a screen. The screen will clog over time and at higher rpms where the engine requires more fuel. This restriction keep engine from producing power and turning up rpms.We have to look somewhere you haven't looked. You have done everything to the engine leaving another source for the problem. That would be the boat side fuel system. Does this make sense? Post back with findings and questions.

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