351w tuning problems
Printed From: CorrectCraftFan.com
Category: Repairs and Maintenance
Forum Name: Engine Repair
Forum Discription: Engine problems and solutions
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=3984
Printed Date: November-23-2024 at 3:04pm
Topic: 351w tuning problems
Posted By: 81nautique
Subject: 351w tuning problems
Date Posted: June-25-2006 at 3:47pm
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.
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You can’t change the wind but you can adjust your sails
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Replies:
Posted By: Bradley950
Date Posted: June-26-2006 at 12:43am
Look for a vaccum leak around the intake and the carb, tighten all of the bolts on the carb, bowls and baseplate. Look at the accel pump and make sure it's giving you a full squirt of gas for the full stroke and the float maybe a shade high. Spray carb cleaner around the base of the carb and the intake. If it smooths off or revs you have a intake leak.
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Brad Miller
bradley950@yahoo.com
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Posted By: 81nautique
Date Posted: June-26-2006 at 6:14am
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?
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You can’t change the wind but you can adjust your sails
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Posted By: 79nautique
Date Posted: June-26-2006 at 11:12am
makesure that the baseplate of the carb and all of the other screws and good and tight. The accel pump will not effect base idle.
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http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique
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Posted By: 81nautique
Date Posted: June-26-2006 at 1:31pm
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.
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You can’t change the wind but you can adjust your sails
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Posted By: 81nautique
Date Posted: June-26-2006 at 1:53pm
79,
I pulled all plugs yesterday thinking I would find a fouled plug from a too rich situation. Surprisingly all looked fairly normal. Started the engine and pulled each plug wire, found 3 cylinders that did not seem to be firing but I have a spark jumping from the plug wire to the plug if I hold it away an inch or so. Now I'm thinking to
lean, no fuel in those cylinders at idle.
#8 plug was differnet than all the others in that it looked brand new white porcelan. Talked to Vince at skidim and he suggested that I may have water entering the cylinder from an exhaust manifold leak.( new riser gaskets on this winter and I didn;t see anything that would indicate I had a problem) He thinks that plug looks new because it is essentially getting steam cleaned. I still think I have a carb issue not electrical.
How do I check for leaky/rusted out exhaust manifolds other than taking them off the boat?
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You can’t change the wind but you can adjust your sails
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Posted By: 79nautique
Date Posted: June-26-2006 at 2:03pm
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?
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http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique
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Posted By: 79nautique
Date Posted: June-26-2006 at 2:12pm
Alan when you re-built the carb did you soak it in a tank of carb cleaner or just use can's of cleaner?
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http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique
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Posted By: 81nautique
Date Posted: June-26-2006 at 2:16pm
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.
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You can’t change the wind but you can adjust your sails
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Posted By: 79nautique
Date Posted: June-26-2006 at 2:28pm
don't buy a new cap and rotor if they where replaced recently they should be fine. The idle is a carb or vaccum leak issue. Just wanted to make sure something else wasn't appearing as a carb issue.
Try disconnecting the throttle linkage at the carb and then adjust the idle mixture screws and varify that the shift linkage doesn't need adjusted as well. If it is off you could be pulling it off the idle circuit of the carb.
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http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique
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Posted By: 81nautique
Date Posted: June-26-2006 at 2:42pm
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.
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You can’t change the wind but you can adjust your sails
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Posted By: 79nautique
Date Posted: June-26-2006 at 3:12pm
have you checked the timing?
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http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique
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Posted By: 81nautique
Date Posted: June-26-2006 at 4:17pm
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.
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You can’t change the wind but you can adjust your sails
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Posted By: 79nautique
Date Posted: June-26-2006 at 4:24pm
I'm leaning towards the carb isn't quit right internally, dirty idle passage or spacer plate carboned up.
disconnect the thottle cable at the carb, adjust your base idle, check the timing leave at 8-10, then re-adjust idle mixture screws.
Before you do anything tighten all the bolts on the carb, intake and make sure the PCV valve is good and there are no leaks coming from it either.
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http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique
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Posted By: stang72
Date Posted: June-26-2006 at 8:45pm
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.
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stang
Face plants are not that funny when it's you face!
http://www.correctcraftfan.com/diaries/images/3720/photo1.jpg" rel="nofollow - The Super Air
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Posted By: 81nautique
Date Posted: June-26-2006 at 10:04pm
All fixed guys, I pulled the primary bowl and the metering block. Tool out the idle mixture screws and blew some compressed air throught the port. Small piece of something came flying out. I assume that was blocking the orifice and was acting like one side mixure was not even open.
This boat sat for a couple of years without being used and the inside of the bowls was filthy, I guess I didn't clean it out well enough when I rebuilt it. Put everything back together and it idle beautifully right away. If it happens again atleast I know where to go.
Thanks for sticking with me on this one Chris.
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You can’t change the wind but you can adjust your sails
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Posted By: 79nautique
Date Posted: June-27-2006 at 7:30am
good deal
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http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique
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