1997 Mercury Force 90hp and 16ft. Bayliner speed lag?

[RBKY]

First up, new to forum and my apologies if this goes long.

I just bought this boat couple months ago and was told top speed was around 35-40 mph due to a larger propeller installed (not sure of specs). I took boat out and first few times it did start rough and top out at 35mph, but no other issues aside from the tach not working.

I bought new battery and that resolved starting issues. The boat seems to sound ok per a buddy who has a similar sized motor. My boat has now sunk to a top speed of 25mph. I was told that a new set of plugs may help. I also was told to run a can of Seafoam thru to clean up and carb. build up and that could also help get the speed up into 45-55mph range?

So, my question is does the new plugs and such sound like it could fix the speed lag and should I put a new propeller on to also try to pick up the lost mph?

Thanks so much for any help!!

 

[Frank Acampora]

Re: 1997 Mercury Force 90hp and 16ft. Bayliner speed lag?

First off, a 90 will not get the 16 foot hull into the 55 MPH speed range. Anyone who tells you different is blowing sunshine up your butt. Running well, propped correctly and given enough fuel, maybe 45.

As to your lack of speed now, fouled plugs usually only give problems at starting and idling. Because of the ignition type, they usually run well at high speeds.

Many things can cause loss of speed. You need to check and clean the carbs, don't just seafoam them. Check the fuel pump and rebuild with new valves and diaphragm. Check the ignition to see that ALL cylinders are firing, and check compression to eliminate mechanical problems.

Definitely repair or replace the tach--it is more useful and important than the speedometer and absolutely necessary when changing props.

 

[RBKY]

Re: 1997 Mercury Force 90hp and 16ft. Bayliner speed lag?

Thanks so much for the reply, sounds like I will follow the advice you posted and see what happens.

Take Care, and again thank you!