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Mercury 500 Needs more throttle

B

Bob in Tennessee

Contributing Member
When my 1977 Mercury 500 runs at full throttle it seems to me to not be wide open. If I back off my throttle stop screw to get more RPM's, do I need to do anything with timing as well?
I used to get 30MPH on my boat but after a trip to a mechanic to help me solve leaking carb issues, I am only getting 27 MPH and the RPM's don't sound as high. The mechanic told me timing was way off. He adjusted timing. The engine does run and sound good, just not the throttle I am used too.
thanks
 
Water pump impeller changed ??----Start with a compression test , post your numbers.-----Inspect exhaust for blockage?-----Is boat getting water logged.-----Make no timing / linkage adjustments unless you are 100% sure there is an issue with them.
 
water pump impeller not changed since last winter. compression test 125 psi on all four. No exhaust blockage. Boat not waterlogged. Just doesn't seem to get the RPM's it did before my mechanic reset timing. Runs good and smooth though.
 
The only reason I can think off (that the motor is happier at less throttle) is that the timing is too far advanced.

Jeff
 
Thanks you!
turned out my bottom carb was leaking at blue plastic inlet. Has to remove carbs to fix. Now she seems to be running pretty well.
Thanks again all!
 
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