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1977 402 40hp won’t ideal

T

twin2turbo

New member
Hello, I just bought stroke 402 2 stroke. it runs but won’t ideal and has very little power. Where do i start, carb or maybe timing?
 
IF that gage is accurate, those are dead low compression numbers--one expects at least 140 pounds compression on those motors.

I suggest you beg/ borrow another gage and see what it says before going any further. You might be able to borrow one from Auto Zone.

Jeff
 
Excellent! Next comes rebuilding the fuel pump (that can leak fuel into the motor) and then the carb.

Jeff
 
I ordered all the parts.

I was looking at the fuel pump today (haven’t removed it yet) and noticed that water from the motor passes through the fuel pump before exiting the motor. So am correct in assuming that the water passing through the fuel pump powers the pump?
 
No; it merely cools it. Vacuum pulses from the crankcase operate it and, if the diaphragm is leaking, will cause rough running.

Jeff
 
Maybe some simple steps;
Have you used non-ethanol gas?
Have you used new plugs?
Re-adjust the idle mixture screws on your carbs - in neutral first, then under load in gear with the prop in water, set toward being rich (some fellas say 1/4 turn richer); then set the idle rpms using throttle adj. screws and set to factory spec or a bit higher - the specs for my old '92 Merc say 750 in gear but it runs smoother at 950 with no stress on the shifting gears.
Last, check electrical components - see http://www.marineengine.com/boat-fo...68-Yet-Another-Merc-40-2-Stroke-With-No-Spark
 
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