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Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 11052
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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I have a 4.3L Mercruiser new short block and ignition, its

Customer Question

Customer: i have a 4.3L Mercruiser new short block and ignition, its got a holley 4160 450cfm carb on it with headers.
JA: Thanks. Can you give me any more details about your issue?
Customer: the problem is it does not have the top end it just bogs down after 4100 rpm and the other motor in the boat is new as well but can do 5200 rmp any thoughts on what adjustment to make
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Submitted: 1 year ago.
Category: Boat
Expert:  Jason replied 1 year ago.

Hi Bob, my name is Jason.

It could be starving for fuel. Have you hooked up a fuel pressure gauge to see if it has any fuel pressure when the engine bogs down?

Customer: replied 1 year ago.
I tried a new fuel pump already before contacting you
Have checked timing too next vacuum?
Or other comments?
Expert:  Jason replied 1 year ago.

What was your fuel pressure actually reading at 4100 rpms? Also, what kind of story does this engine have? When did it last run correctly? Was it sitting a long time?

Customer: replied 1 year ago.
I don't have a pressure guage for this, so I swapped the electric fuel pump from the other side which worked fine. (twin engines)
Same problem, the starboard engine still bogs down at 4100rpm and the other motor runs fine up to 5200rpm so not a pump problem. changed the main filter again just to make sure that was not it.
I am going to check the vacuum on the motor and adjust the idle jets on primary using it as there are no secondary adjustments . I am wondering as the 4160 is a single pump carb with vacuum assist secondaries, could there be a problem with the power valve in the carb? The secondary's butterflies are open at WOT when you look into the carb, but it sounds like its really wanting more fuel, bogging .
Expert:  Jason replied 1 year ago.

The idle jets only flow fuel at idle speeds, and they have nothing to do with full speed operation.

Is there a story with this engine? Have you ever seen it make full power under a load?

Customer: replied 1 year ago.
Its a new short block with a new Elderbrock aluminum intake manifold and Holley 4160 PART# ***** new electronics, from Summit Racing.
Its never had good top end power on the starboard motor. So yes I am troubleshooting an old ongoing issue.
Expert:  Tan replied 1 year ago.

Hello. My name is Tan.

Have you tried swapping the carbs to eliminate that as a possible cause?

Do both engines run off the same fuel tank?