351w tuning problems

Brief history.

1981 351w 300hours.

On our first real outing this spring the boat started having problems idling. Felt like it wanted to die out and on initial throttle it would bog. Once it seemed to get past a certain point it would run pretty good up to wot. Carb was leaking fuel so I thought I would rebuild it. That has been done.

Yesterday out for a ride the boat ran awesome for about an hour, we were cruising at about 2000rpm. Slowed to dock and my idle problem was back terribly. Could barely keep it running. Again once I got past idle it would scream up to wot. I thought it was running rich as I had black soot on the transom below the platform, pulled plugs today and I was surprised they didn't look black.

Decided to adjust idle mixture, put a vacuum gauge on as per Holley procedure and tried to adjust up to the highest vacuum I could get. 16-18 on the vacuum gauge at idle but it was erratic. 2.5 turns on the mixture screws seemed to be about right and thats where I had them set so no change. Timed the boat again and tried 6 to 10 before, no real change.

It just idles terribly and has a bog when gassing it. Once it goes past about 1200 rpm it's fine.

I installed an electroninc conversion kit this winter along with new cap,rotor, wires, plugs and matching coil for the conversion. Everthing is new.

Where do I go from here.

Brad,

Sprayed carb cleaner all around carb and intake with no change.

Will the accelerator pump affect idle, or just the initial throttle up or both?

I'll check for vacuum leaks again tonight. Other than that do I order a new carb since I really don't know what I'm doing with the old one. I rebuilt it but doesn't mean it was done right. Seemed pretty simple but I could have screwed something up.

it's really hard to check if it is leaking odds are against it, not saying it's not possible. I would think that it could be on the lean side which will give you a cleaner looking plug as well. I'll have to go back and reread some of your post and get back. What's the inside of the cap and rotor look like, no carbon tracks or cracks or corrosion?

Inside of the cap and the rotor itself look pretty good, less than 10 hours on the entire tune up this year. I'm going to order a new cap and rotor to try , if that's not the problem I'll have them for next years tune up so it's worth a shot.

79
Make sure I understand how to adjust the idle mixture screws.

I have disconneted the throttle linkage, attached a vacuum gauge. back out or open the mixture screws until rpms increase and adjust to highest vacuum reading possible. I did this and 2.5 to 3 turns out seems to be where it's best but still idle like crap. I actually have to adjust the curb idle up to keep it from stalling when I drop it in gear.   Engine should idle on it's own without any curb idle added right?

I'm gonna open the primary side of the carb tonight and make sure theres nothing (dirt) inside the bowl that could be causing a problem.

Yes, Timing has been set at both 6 and 10 BTC with no change. But I'm not sure if it's correct because of the idle problem, Would that affect the timing reading I'm getting? It Appears to be advancing properly when I rev it up. I'm going to start from scratch again tonight and try all adjustments again and check one more time for vacuum leaks.

Alan...what did you use for a gasket between carb and spacer? I have had vacc. leaks because that gasket is often a problem...there are many different ones that suppose to fit holley's but are subject to leaks.

good deal