351w stumble and misfire at WOT

‘87 351w, still running points and condenser ignition. Boat start with the touch of a key and will idle and run great until you get over 1/4 throttle. Starts to have a noticeable stumble, then when you mail the throttle it chokes and misfire bad. Can barely get up on plane. If it does get up on plane, cannot go wide open. I have cleaned the carb and made adjustments in all directions with no change, new points and condenser with no change, new plugs (old ones looked great) with no change. Kind of at a loss here. Gets worse as the boat gets warmed up. One thing I did notice is that the plug wires the previous owner installed fit VERY loose into the new cap I installed. Could that cause a misfire under load? I pulled the coil and am going to ohm that today. What are my specs I am looking for on that? Any input is appreciated.

I feel like you have a fuel problem. So, fuel filter, water separator and air pathway.

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Originally Posted by garyholl

I feel like you have a fuel problem. So, fuel filter, water separator and air pathway.

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I have the fuel filter out and replacing today. Sure looks like the filter in it isn’t even the right one for the housing.

Anybody know of a way to test vacuum secondary’s on the Holley carb?

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Originally Posted by Davidst69

I have the fuel filter out and replacing today. Sure looks like the filter in it isn’t even the right one for the housing.

Anybody know of a way to test vacuum secondary’s on the Holley carb?

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Can you have someone ride with you the next time you take it out? They can drive and you can look at the carb whiles its under load and see if the secondaries are opening and if it is getting fuel. When was the last time the carb was rebuilt?

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Originally Posted by secondsupra2004

Can you have someone ride with you the next time you take it out? They can drive and you can look at the carb whiles its under load and see if the secondaries are opening and if it is getting fuel. When was the last time the carb was rebuilt?

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Yes I’ll have to do that on Friday.

I ohm tested the coil, not sure if these readings are ok or not.

Room temp: 1.6 ohm across +/-, 10750 ohm across neg and center post.

Warmed to 150 degrees F: 1.8 ohm across +/-, 12190 ohm across neg and center.

These seem to be a lot higher on the secondary than other members have posted on claimed good coils

Plugs and/or wires? It sounds like an ignition problem to me. Also make sure you're not getting any condensation in the distributer cap from all this humidity and extreme heat.
Several years ago I got condensation in my cap ... the motor started and idled smoothly, but had no power and stumbled so much I couldn't even pull up my skier. Dried things out and it was fine.

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How are you setting to points? The dwell should be about 30 degrees or point gap at .019. I use to be a die hard points fan . Mainly because of the simplicity of operation and ease of repair . I have switched to the Davis Unified Ignition or DUI on all of my 351 equipped boats. Faster starts , excellent performance and 0 maintenance are some of the benefits.

https://i.imgur.com/HxibZ92.jpg?1