Hesitation upon acceleration Mercruiser 5.0

itswink

Seaman Apprentice
Joined
Aug 19, 2011
Messages
35
5.0 mercruiser carbed SN:OW355448

I had another thread but it got moved to the prop section. I was convinced this might actually be a prop problem until I made some improvements. This motor has some hesitation while accelerating, it bounces RPM's a little. Its a small cough. It doesn't seem to be making much power in the lower RPM range.
I have changed plugs, wires, distributor cap, fuel filter / water separator, cleaned the spark arrest, and moved the accelerator pump to the highest setting.
It has improved a lot from where it was, but it still is not as strong as it was earlier this year.
Before I did the tune up, it wouldn't even get on plane.
It still has a little cough in it, as can be heard in the video linked below.
As you can hear, once it reached about 3000 RPM it has no more hesitation or bogging.
What else can I try?

http://youtu.be/xJlA2c_Hotc
 

NHGuy

Captain
Joined
May 21, 2009
Messages
3,631
Re: Hesitation upon acceleration Mercruiser 5.0

Does it make 4500 rpm at wide open? It sounds like it revs up where it should. If no drop to a lower pitch prop.
If yes, have you set the timing? Have you set the main jets?
Do you start out with the trim all the way down-in? You need to do that for sure.
Is there a tremendous amount of weight at the rear of the boat? If so, can some of the weight move forward?
 

itswink

Seaman Apprentice
Joined
Aug 19, 2011
Messages
35
Re: Hesitation upon acceleration Mercruiser 5.0

This was done with just me and one other person. It is trimmed all the way down. It revs to max at top end.
I am going to check the timing tomorrow. I haven't done anything to the carb but change the setting on the accelerator pump.
 

NHGuy

Captain
Joined
May 21, 2009
Messages
3,631
Re: Hesitation upon acceleration Mercruiser 5.0

Was it good before?
 

itswink

Seaman Apprentice
Joined
Aug 19, 2011
Messages
35
Re: Hesitation upon acceleration Mercruiser 5.0

Yes, earlier this season it was good. Just a few days ago it wouldnt even plane out with me alone. It has gotten much better with the above fixes, but it still isn't like it was.
if i hammer down fast, it will plane out okay, and I mean lay it down as fast as possible.
I can tell if it is going to go or not by initial RPM. If it starts off closer to 3000 it is going to plane out decent. Sometimes when I drop the hammer is starts around 2600, and surges just a little up and down, but takes a while to plane.

In this video, it took about 20 seconds to plane with 2 people and under a half a tank. Usually it still takes longer.
It didnt used to take this long with a light load.
 
Top