4.3L OMC-Hesitates on hole shot, sometimes at 1000-2000RPM

[took-the-red-pill]

1988-4.3L V6 with cobra leg. 2BBL carb. 16-1/2' bow rider. We tow skiers and tubes.

Two months ago my boat was really running rough. I put in a new carb kit-I'm not an expert, so I just took it apart, cleaned it, and put back together with the new parts, and cleaned the fuel filtre.

After the kit it was starting and running well, but really hesitating on hole shot. As I recall it stalled occasionally. I backed off the idle screws about 1/2 turn and it became manageable, and would not stall.

Currently:
Starts and runs well. WOT is about 4400RPM with my current 15 pitch prop.

Hole shot-I punch it, it hesitates maybe 1/2 second, then takes off. Once it takes off, it feels like normal acceleration.

Sometimes at about 1000-2000RPM, when I'm already moving, if I punch it, it almost dies-the tach drops to 0 for a moment, then it catches and takes off.

A few times, also at that low RPM if I hit the throttle, it has gone, "flup flup flup," and then taken off.

On the advice of my brother, who thought it might be accelerator pump, I checked the accelerator pump by having my son actuate the throttle with it turned off. The first few times, one of the accelerator jets was a bit lethargic, but after that both worked well.

Please let me know your thoughts on what my situation might be, and where to start.

Thanks
Keith

 

[Boomyal]

Re: 4.3L OMC-Hesitates on hole shot, sometimes at 1000-2000RPM

You didn't say what brand of carb you had.

 

[took-the-red-pill]

Re: 4.3L OMC-Hesitates on hole shot, sometimes at 1000-2000RPM

It says "GM 2 jet Rochester." Don't know if there is any other pertinent information that I have left out.

I run premium fuel only.
I'm at 4000 feet, in Western Canada.
Oil pressure is excellent: 40 at idle and about 75 when cruising.
To start I pump it in neutral maybe 2-3 times and it fires up right away.
It behaves very well when cruising at any speed, the only issues are when I give it throttle.

Thanks for any input on this issue.
Cheers
Keith

 

[Boomyal]

Re: 4.3L OMC-Hesitates on hole shot, sometimes at 1000-2000RPM

I am certainly not a carb expert but I do know that there are 'transition slots' in the venturis that provide more fuel as the butterflies move up past them on the initial throttle opening. The bottom of the slots are usually just above the butterflies when they are at idle position. As the butterflies pass them, on the way to opening, they become subject to venturi vacuum and begin to draw in more fuel. Maybe yours are dirty or plugged up. The rpm that you mention is right about where they should be supplying fuel.