Stumble during acceleration

[silvert]

First off, I'm new here. Great site!

Second, I am newer to boats, at the end of last summer I bought my first boat.

I bought a '95 maxum 2000 sr with a 4.3 LX. I bought the boat dirt cheap because it had a cracked block. Other than that, the boat was in great shape. I have been a drag racer since I was 18 and have always built my own cars and drivetrains. I took on getting this boat running with no prior knowledge of boats. This website and a few others were great in helping me get it running. I rebuilt a 4.3 and installed it myself. Wasn't that bad of a project really. The boat came with a newly rebuilt carter 4bbl carb. My only problem is...well, I'm carb dumb. I'm a fuel injection person. I can tune a fuel injected car...but not a carbed boat lol.

Anyways, the boat runs great. It has no issue going 46 mph with 4 adults on board (gps). I have been battling this stumble since day one though. If I ease into it, it is fine. But if I give it a lot of gas to get out of the hole quickly, it stumbles pretty bad.

What I have verified:
-I've run probably 6 full tanks of gas through it so far, so that eliminates bad gas imo
-verified correct timing per mercruiser specs, also verfied advance is working correctly
-new plugs and wires
-choke is operating correctly. After about ten minutes, choke is wide open.
-no binding in the secondary linkage
-haven't touched the fuel pump
-boat runs solid at 180 degrees
-oil pressure is 40 at idle, goes to 60 or so at wot
-no problem at 4500 rpm
-haven't tried octane better than 89, but it is not knocking or pinging on 89
-gave it a couple extra degrees of timing, no improvement
-played with the accelerator pump a little, but kind of clueless on that besides making sure it is squirting gas the whole range of throttle application
-played with the air screws. This helped a little but didn't completely solve it.

I think that's about where I stand right now. Any suggestions would be greatly appreciated.

Thanks!!

Kevin

 

[silvert]

Re: Stumble during acceleration

Here is a pic I took of the boat. This was at Brookville Lake in SE Indiana. About 30 minutes from home. I live about 10 minutes from the Ohio river, which we (the family) frequent the most.

 

[silvert]

Re: Stumble during acceleration

The intake looks like it would fit a quadrajet better. It has the small primary openings and the larger secondary holes. Is there a quadrajet that will fit, linkage and all? I do know a little more about those. I know I can get a holley 4bbl to work, is there a marine holley out there that will bolt up? I think I've seen adapters to go from a quadrajet intake to a holley carb. Would be cool to swap the carter for a holley. Just worried all the linkages would not be a direct fit.

 

[series60]

Re: Stumble during acceleration

The typical stumble on hard acceleration points to two items. Accelerator pump and/or distributor. With the carb apart inspect the accelerator pump rubber for wear and the pump bore for scratches? Just because someone says 'newly rebuilt carb' doesn't mean it was done right! A picture of the your carb set up would be helpful.