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Tan
Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10621
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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I have recently purchased a 1980 Bass Tracker with a 40 hp

Customer Question

I have recently purchased a 1980 Bass Tracker with a 40 hp Mercury motor . Everything is original to my knowledge. The motors running great idle and up to 3/4 speed . When attempting full speed the motor starts missing very bad and continues until I back it back down to about 3/4 speed. I have replaced fuel, fuel line and spark plugs. I have also ran sea foam thru the tank several times. What else could I check?
Submitted: 1 year ago.
Category: Boat
Expert:  Tan replied 1 year ago.
Hello. My name is***** this issue seem like a fuel or spark issue? Is the miss abrupt or slowly comes on? When you are running the boat and it is acting up squeeze the primer bulb. Does the engine run better? Push the choke when engine is acting up. Does engine run better? Could I get the engine serial number please? Do you have a timing light?
Customer: replied 1 year ago.
Tan,
I feel like it is a fuel or carb issue but will check out all your questions and get back to you. I assumed if a spark issue it would surface at any speed?
Thanks
Expert:  Tan replied 1 year ago.
The fuel is the most common issue. Spark will be intermittent and can occur at any rpm. Post back with findings and questions. The tests I posted will tell us if you have a fuel related issue and which part of the fuel system is the issue.
Customer: replied 1 year ago.
Tan, I plan on going though the list of items this weekend , so more to follow.
Scott
Expert:  Tan replied 1 year ago.
Ok Scott keep me posted......Thanks.
Customer: replied 1 year ago.
Tan,
I checked out of the items you mentioned. First , squeezing the primer bulb had no effect to the motor when acting up. Second, when choked the motor died immediately. I do not have a timing light.
Lastly the motor serial number is #5559423
Scott
Expert:  Tan replied 1 year ago.
Hi Scott. We need to check for a misfire with the timing light. Connect the timing light to one spark plug wire at a time run the boat watching the flash of the timing light when the engine starts acting up. The flash must be staedy with no misfire. If you have any dead spots on one cylinder then swap that coil with a known good firing coil. If the misfire moves then that coil is bad. If you have no misfire squeeze the primer bulb when the engine is acting up do the same with the choke. All these tests must be done when the engine is acting up. Post back with findings and questions.
Customer: replied 1 year ago.
Sorry if I confused but I did choke while acting up and the engine died immediately.
On timing I'll get that checked out.
More to come lol
Expert:  Tan replied 1 year ago.
Ok I didn't know if you had done the check with engine acting up or not. How about the primer bulb test? These tests are just eliminating a carburetor issue or fuel starvation issue.
Customer: replied 1 year ago.
Yes , squeezing the primer bulb had no effect on the motor when acting up.
Expert:  Tan replied 1 year ago.
Ok we have eliminated the fuel system leaving an ignition issue. This is where the timing light test comes in to play. Do this test and post back with findings.

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