If the timing is set correctly the next thing I would check is the
accelerator pump on the carb. Looking down into the carb with the
engine off you should see it squirt gas into the throats when someone
briskly pushes the accelerator.

wrote:
Hi Guys,

Just a quick question. I've got a 1996 5.7 litre Mercruiser with Carb.
I replaced the ignition leads, distributor cap and rotor last night
and the boat is now running much smoother than it was.

However, when I was testing the engine (without putting it in drive) I
noticed that if the engine was throttled up at a slow/medium rate it
revs smoothly. However, if the throttle is gunned, it bogs down for a
moment and then revs up.

The above is what happens when it is warm. If the engine is cold you
have to be really gently with the throttle or else the engine acts as
if it is about to stall unless you throttle back quickly.

The flame arrestor is clean and all the filters are new. I'm fairly
sure that it was like this before I replaced the ignition bits last
night - it's just that now that the engine is running smoother it is
more noticeable.

None of this really matters in the way I use the boat normally. I
always leave the engine warm up before leaving the dock and I'm not
heavy handed with throttle normally. I'd just like to sort this
problem out is case it has any knock on effects on the engine down the
line.

Is there any chance you could let me know the most likely cause of this
is? Is it normal?

Thanks in advance for any help,
Paul.