Hesitation on 351W

orttauq

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1976 American Eagle (American Boat Company) with 351W; new Edelbrock 1406 600 CFM 4-Barrel Carburetor, Edelbrock Performer intake (older version), Edelbrock 1791 Electric Fuel Pump and Edelbrock Max-Fire Distributor. New ½ inch fuel hose from new vented tank to remote spin-on fuel filter/water separator then to pump. Mercruiser 888 but I do not know the pitch.
Runs very strong out of the hole at WOT to just short of 5k RPM but then 5-10 seconds later it starts to hesitate. Back it off to ~4500 and it runs okay again. Back to WOT and it hesitates again. The carb has the original jets. I think when I am backing it off it is running on 2 barrels but not sure, just sounds like it.
The 1791 fuel pump with 120 GPH is what the tech specs for the 1406 say it should be running but is this issue it running out of fuel? Any ideas?
 

Bondo

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1976 American Eagle (American Boat Company) with 351W; new Edelbrock 1406 600 CFM 4-Barrel Carburetor, Edelbrock Performer intake (older version), Edelbrock 1791 Electric Fuel Pump and Edelbrock Max-Fire Distributor. New ½ inch fuel hose from new vented tank to remote spin-on fuel filter/water separator then to pump. Mercruiser 888 but I do not know the pitch.
Runs very strong out of the hole at WOT to just short of 5k RPM but then 5-10 seconds later it starts to hesitate. Back it off to ~4500 and it runs okay again. Back to WOT and it hesitates again. The carb has the original jets. I think when I am backing it off it is running on 2 barrels but not sure, just sounds like it.
The 1791 fuel pump with 120 GPH is what the tech specs for the 1406 say it should be running but is this issue it running out of fuel? Any ideas?
Ayuh,..... That's a unsafe automotive carb, the marine version is the 1409,....
 

Scott Danforth

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600 CFM is a bit light for 351 cubes. I run a bigger carb on a V6. Not to mention the automotive carb issue.
 

orttauq

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Well now you have me searching back through orders, I thought it was 1406 but I am sure it is a marine carb because @Bondo said what to get...
 

Scott06

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Ok just bad memory. It is a 1409 Marine 600cfm.
Doubt you are running out of fuel supply -what do the plugs look like and are you sure your ignition is not missing or hitting a rev limiter?

You may need to put in fatter secondary jets or try richer step up rods on the primary. the carb book from edlebrock is available on line has calibration charts for the 1409
 

orttauq

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Pretty sure it is not ignition, it is not a misfire since that would be more of a stumble. I have not looked at the plugs but can pull one to see. What I have is like not enough fuel so I like the suggestion to look at the secondary jets. Never heard of step up rods so will read up. Thanks
 

Scott06

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Pretty sure it is not ignition, it is not a misfire since that would be more of a stumble. I have not looked at the plugs but can pull one to see. What I have is like not enough fuel so I like the suggestion to look at the secondary jets. Never heard of step up rods so will read up. Thanks
All carbs will have some type of enrichment system that kicks in as you get to WOT. Usually runs off vacuum that drops as throttle opens.

on an edlebrock there is a step up rod that goes down in the primary jets that restricts the fuel at part throttle and cruise, at full throttle lower vacuum signal will allow the springs to step the rods to up to the rich position and fatten up the mixture. you can change the rod to smaller or larger diameter( richer/leaner) , and change the springs to affect when it goes from lean to rich. On a edlebrock this is easily done by removing two torq screws on top of air horn , no need to remove bowl top.

all this is outlined in the edlebrock manual here https://www.edelbrock.com/media/wys...RyR9Eh70CNVa18t4bcXik-_6Fj6QKMoJfMlPvQZFmh0mT
 

orttauq

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Thanks @Scott06. That helps to know that. I have been reading up and pretty much across the board I see that the 600 CFM is what is needed for marine applications; either Edelbrock or Holley.
 

Scott06

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Thanks @Scott06. That helps to know that. I have been reading up and pretty much across the board I see that the 600 CFM is what is needed for marine applications; either Edelbrock or Holley.
I think either a 600 or 750 will work on a stock engine that size. When I bought my partial engine from michigan motorz in 2016 they were using 600 cfm edlebrocks (1409) for the 5.7 L engines, while Mercruiser will use a 750 webber/edlebrock on their 357 reman engines...

Since you already have a 1409 try tuning it.

I also had a lean spot during holeshot that was due to slop in the accelerator pump linkage, I didn't figure this out until I put the AFR meter on the boat and saw it go way lean when I stabbed the gas but the engine took a long time to recover, I was increasing jet size which ultimately was not the issue. bent the linakge rod a little longer so it was under spring tension from accel pump and that took care of it, also put in a bigger pump nozzle.

when reading the plug you have to run a bit at what ever rpm you are trying to see , then cut the engine off and pull the plug, otherwise you are just reading mixture at idle

the charts in the eddy book are super helpful for tuning part throttle vs WOT
 

Lpgc

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My 302W started having similar problems, would run OK at part throttle but seem like it was leaning out at full throttle. The problem got progressively worse, it started doing it at lower throttle settings. Some who have contributed to this thread suggested it might not be a carb or ignition problem, it could be that the none return valve in the fuel pickup pipe at the tank was stuck or clogged, I checked that and found it was stuck/clogged, cleaned it all up and the problem hasn't re-occurred.
 

orttauq

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My entire fuel system is new, including tank to carb without backflow (not needed with electric). When I am next on the water I am going to see how it does from idle to WOT out of the hole (I rarely do this-I am either at speed and go WOT or pulling a skier up and that is nowhere near WOT)
I tried to get the Edelbrock 1488 Performer Series Carburetor Calibration Kit but on back-order from all the usual places. Thanks all
 
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