5.7 Vortec Runs Great On Land but Bogs Under Load in Water

[carrera205]

I'm at a loss here. My 5.7 Vortec runs like a top in the driveway on muffs but when i put it in the lake under load it can't get above 1700-2000 rpm without sputtering and trying to die. I can put it on muffs in the driveway and take it up to 3k and it purrs but put it in water and it wants to die. I've tried just about everything I can think of maybe ya'll can help me here because I'm stumped.

Here are the details.

5.7 Vortec
Edelbrock 1409 Carb (just rebuilt for good measure)
Put a Digital Timing Light on it to dial in the fuel-air mix
Timing Set to 8 degrees BTC
Holly Electric Fuel Pump keeps constant 7-8 psi to carb
Thunderbolt 4 Ignition

 

[jimmbo]

Running the Muffs means Sweet F all. No backpressure so the engine can run and sound fine even if 1/2 the cylinders aren't firing
Compression Test
Is the ignition System providing a Good Spark to all Cylinders? By Good, I mean, can the spark jump a 3/8" gap?
Fuel System, is the engine getting enough gas from the Fuel Pump?
Even a misadjusted Throttle Cable can mess up the Engine's power output

 

[Searay205]

Air mixture isn't set with timing light, it set with a vacuum gauge. Google or search engine masters, its a tv show. About a month ago they explained how a Holley Carburator worked, the theory and how to adjust.
You set fuel mixture to highest rpm then readjust idle. What is your full advance timing? Who cares about base timing. Sounds like your running lean, is your fuel filter clean?

 

[Lou C]

The anti siphon valve at the gas tank fuel line connection is a possibility

 

[Scott06]

I'm at a loss here. My 5.7 Vortec runs like a top in the driveway on muffs but when i put it in the lake under load it can't get above 1700-2000 rpm without sputtering and trying to die. I can put it on muffs in the driveway and take it up to 3k and it purrs but put it in water and it wants to die. I've tried just about everything I can think of maybe ya'll can help me here because I'm stumped.

Here are the details.

5.7 Vortec
Edelbrock 1409 Carb (just rebuilt for good measure)
Put a Digital Timing Light on it to dial in the fuel-air mix
Timing Set to 8 degrees BTC
Holly Electric Fuel Pump keeps constant 7-8 psi to carb
Thunderbolt 4 Ignition

Describe in detail what happens when on the water does the rpm not go up or does it sputter when advancing the throttle. Does it die when you put it into gear?
as discussed on land there is no load on engine so it doesnt need to make any power to rev to 3 k

 

[Scott Danforth]

I'm at a loss here. My 5.7 Vortec runs like a top in the driveway on muffs but when i put it in the lake under load it can't get above 1700-2000 rpm without sputtering and trying to die. I can put it on muffs in the driveway and take it up to 3k and it purrs but put it in water and it wants to die. I've tried just about everything I can think of maybe ya'll can help me here because I'm stumped.

Here are the details.

5.7 Vortec
Edelbrock 1409 Carb (just rebuilt for good measure)
Put a Digital Timing Light on it to dial in the fuel-air mix
Timing Set to 8 degrees BTC
Holly Electric Fuel Pump keeps constant 7-8 psi to carb
Thunderbolt 4 Ignition

Which Holley fuel pump do you have?

The marine ones flow more that you would need with twice the motor. 7-8 psi is on the edge of holding the needle open on the 1409

What is your compression numbers?

What do the plugs look like?

 

[tank1949]

I'm at a loss here. My 5.7 Vortec runs like a top in the driveway on muffs but when i put it in the lake under load it can't get above 1700-2000 rpm without sputtering and trying to die. I can put it on muffs in the driveway and take it up to 3k and it purrs but put it in water and it wants to die. I've tried just about everything I can think of maybe ya'll can help me here because I'm stumped.

Here are the details.

5.7 Vortec
Edelbrock 1409 Carb (just rebuilt for good measure)
Put a Digital Timing Light on it to dial in the fuel-air mix
Timing Set to 8 degrees BTC
Holly Electric Fuel Pump keeps constant 7-8 psi to carb
Thunderbolt 4 Ignition

make sure all plugs are firing or you don't have a plug wire that has come loose. MC have some very sturdy engine mounts that can mislead boaters into thinking that all plugs are firing. Also, manually advance throttle while pointing timing light at timing tab to check if ignition is advancing.

 

[dubs283]

I think a tune up (baseline) is in order. Guessing t bolt ignition, sensor on the dist can cause issues too......

Funny how you have a weber carb but suggestions on how tos on holley are suggested

 

[Scott06]

Funny how you have a weber carb but suggestions on how tos on holley are suggested

yeah no idle adjustments make sense here.
holley fuel pump comments scott makes are spot on though

 

[carrera205]

@Scott06 it'll go into gear and i can roll around up to roughly 1500-1700 RPM but anything higher and it wants to bog down and die so I'll come off it and it'll keep running.

I pulled the plugs today and all but one we're decently black like it's running rich. One plug was pretty clean however so wondering if that one maybe wasn't firing. The wires were in all the right places. I'll post some pics later. I'm pretty certain the fuel pump is keeping constant pressure to the engine.

Based on all of your comments I'm going to start with the following

1. Change all spark plugs
2. Change all plug wires
3. change the distributor cap and maybe the ignition sensor
4. Once it's back together i'll get a vacuum gauge on it and see what's happening with the fuel/air mix.

I need to inspect the anti-siphon fitting but not sure where that might be. I have two tanks that feed into a switched diverter so i can be between tanks then from there it feeds to the fuel pump then to the fuel filter and then into the carb. I replaced the fuel filter and the pre-filter to make sure it wasn't clogged.

 

[Rick Stephens]

Sounds to me like more in depth carburetor cleaning needed. Not plugs or ignition. A compression check will tell a lot.

 

[carrera205]

Sounds to me like more in depth carburetor cleaning needed. Not plugs or ignition. A compression check will tell a lot.

I pulled it apart and rebuilt it making sure to clear out every passage, jet, etc. not sure what else I could’ve missed.

 

[Rick Stephens]

Bogging out in midrange sounds like needles aren't pulling up properly. Check the ability of the vacuum powered plunger to move freely.

 

[Scott Danforth]

Regarding the 1409 Edelbrock

Do not use more than 6.5 PSI fuel pressure. Excessive fuel pressure may cause flooding. If your fuel pressure is too high, install an adjustable pressure regulator, such as Edelbrock #8190.

 

[Scott06]

Bogging out in midrange sounds like needles aren't pulling up properly. Check the ability of the vacuum powered plunger to move freely.

Agreed would check fuel supply and pressure then re rebuild carb

 

[Scott06]

I pulled it apart and rebuilt it making sure to clear out every passage, jet, etc. not sure what else I could’ve missed.

Based on being rich would think the needle and seat/ float arent working or power piston is stuck in rich position. Dose it have the stock jets and step up rods in it? Would make sure vacum isnt low for some reason which would make it go rich all the time

 

[Rick Stephens]

Based on being rich would think the needle and seat/ float arent working or power piston is stuck in rich position. Dose it have the stock jets and step up rods in it? Would make sure vacum isnt low for some reason which would make it go rich all the time

No power piston. Just mains and secondary jets and vac powered needles on the main jets.

 

[Searay205]

The reason I suggested the engine builders Holley video is to UNDERSTAND how a carburetor functions. How the power valve interacts with other components, how jet sizes are determined. Once you understand how or the physics troubleshooting becomes efficient vs monkey see monkey try.

 

[Scott Danforth]

However Holley and Edelbrock have completely different setups, designs and tunability which will confuse all but a diehard gearhead

 

[Lou C]

That’s true then on older boats you have Quadrajets which are totally different from those 2.