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'Stumble' during hard takeoff

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It's not a Malibu, but the answers should be consistent for any 5.7L carbed engine....

I'm getting a stumble pretty consistently during hard take-offs. Sometimes it's worse than others (almost dies vs hardly noticable), but the stumble is generally there. This is a Volvo(GM) 5.7 carbed (2BBL Holley) engine. Fuel filters have been replaced since the stumble started.

The carb was rebuilt because the accelerator pump diaphram was bad about 3 years ago (Backfire during hard takeoff).

Looking for any ideas from the more mechanically inclined on this site.

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It's been a while since the rotor/cap were replaced ('02). All plug wires & coil to distibutor were replaced last spring.

I'll take a look next time I'm on the boat.

It's a little unusual that it would only be an issue between the time the we drop the hammer and the boat starts to take off. Once the boat starts to accelerate, it pulls strongly right up to speed.

Edited by weinrdog
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It sure sounds like the accelerator pump has gone bad again...Holley Carbs are pretty easy to rebuild I would start there. I rebuilt the Holley double pumpers on my Eliminator every year. I was running a blend and the rubber did not seem to hold up.

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Thanks - I'll take a look at it again... The rebuild was fairly easy - finding time on the other hand... Hopefully I can get away with just the accel pump.

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Just so you know, the ignition system is under the most strain/load when the engine is trying to deliver the most power, ie. dropping hammer. Once you're on plane and just cruising, it's much easier on the ignition system. I could be way off in your case, though.

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Check the tranny fluid and add if necessary. Mine once got low and it made the tranny slip, felt like the engine was stumbling, but it was actually tranny fluid.

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Last year, my 350 carb would stumble or die on full throttle acceleration (pulling skier up). The problem was a partially stuck choke. Check your throttle plates, they may be hanging up a bit.

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Thanks for the ideas. I'll dig into it this weekend and let you know what I find - I have a carb rebuild kit & new cap/rotor. I should be able to see the choke while I'm rebuilding the carb.

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  • 1 month later...

Problem solved. I'm not sure what fixed it, but THANKS to all those who replied here - without a lot of time to test each, I cleaned & rebuilt the carb, cleaned spark arrestor, replaced plugs, dist cap & rotors.

The spark arrestor was pretty dirty. There was some crud under the dist cap. The accel. pump looked like it was working, but adjusted slightly incorrectly. Two of the plugs were pretty dark, but the rest looked ok.

Worked great for the entire week on the lake & about 3 tank fulls without a hitch. Thanks again guys!

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