What's a Typical Idle Mixture Setting On A Marine Holley?

[Mutinous_Scallywag]

Engines are 351 Fords with Holley 4160s. Previous owner had the idle mix screws set around 3/4 turns, and the idle was also a little lower than I like. I've since adjusted idle up to about 600 RPM and the mix screws out to 1 1/2 turns.

But that 1 1/2 turns is a typical car setting. Wondering if the physics of it are a little different on a boat engine. I would hook up a vacuum gauge and test, but there's no easy place to do it. I'd pretty much have to yank the PCV hose off the manifold and use an adapter of some sort.

What does your marine Holley typically like for its idle mixture? I know it doesn't spend nearly as much time at idle as a car would.

 

[Scott Danforth]

there is nothing "typical" about carb settings. they are a starting point.

no need for vacuum, you can set the idle mixture screws with an un-lit propane torch. if adding a bit of propane raises RPM, then back out the screws a bit. if adding a bit of propane lowers the RPM, then turn in the idle mixture screws.

however at only 3/4 turn out, I would have suspected a leaking power valve.

does your 4160 have a rear power valve, or just the blocked off metering plate?

Make sure to dial in the point gap and dwell and timing prior to setting the carb mix as dwell and timing have a direct effect on idle speed as well.

 

[Mutinous_Scallywag]

Thanks. Both engines were set at the same 3/4, so I doubt both power valves are leaking. These carbs have rear metering plates.

 

[Scott Danforth]

Thanks. Both engines were set at the same 3/4, so I doubt both power valves are leaking. These carbs have rear metering plates.

all Holley 4 barrels have 2 metering plates

but do the rear plates have a power valve, or a block-off?

 

[Mutinous_Scallywag]

all Holley 4 barrels have 2 metering plates

but do the rear plates have a power valve, or a block-off?

Difference in terminology maybe, but the front has a metering block with jets, power valve, idle screws. The rear does not.

 

[Scott Danforth]

Difference in terminology maybe, but the front has a metering block with jets, power valve, idle screws. The rear does not.

Holley makes about 150 different metering blocks depending on application, then the aftermarket multiplies that by about 10x

All have jets
many have idle mix screws
Most have air bleeds
some do not have power valves
the emulsion tubes, passage size, etc. make up most of the differences.

Most 4160 carbs are set up with the following:
Vac secondary body
primary metering block - main jets, power valve, idle screws, 3-hole emulsion tubes, accelerator pump plumbing
secondary metering block - Secondary Jets, no power valve, no idle mix, 2-hole emulsion tubes, no accelerator pump plumbing

because the lack of a secondary power valve, the main jets are usually increased by 4-6 sizes

 

[Lou C]

I have a Holley 4160 that was set up specifically for the OMC/Volvo 4.3 V6 these had a metering block on the primary side (with no power valve incidentally) and a metering plate on the secondary side (no mixture screws). The primary side jets were increased in size to compensate for no power valve but I'm not sure why Holley deleted the power valve on these.

 

[Redrig]

I dont know if this will be terribly relevant for reasons listed above but I went through this a couple years ago. I had a leaking power valve (running pig rich with idle mixture screws all the way in)

I did a full rebuild on the 2 barrel. My settings ended up at a touch more than 1 , call it 1 1/8 , Like I said though, may not be relevant at all , I am at 5400ft elevation.

 

[Mutinous_Scallywag]

I've been refining my Google searches and finding that the condition I describe is somewhat common for 351W/Holley owners. Many of them seem to end up with a mixture under 1 turn and wonder why that is.

I dunno. Maybe it's the incline of the boat raising the effective fuel level in the bowls, or maybe the floats are just set high (no external adjustment). These carbs are supposed to have blowout protection, but I suppose it's not impossible that leaky power valves are to blame.

This weekend I'm going to fire up the engines again and lower the mixture to see if there's a discernable difference in RPM, or in the noise of the engine.

 

[Scott Danforth]

Never understood why Holley ham-strung the 4160 carbs with the non-adjustable float when the adjustable float is less expensive due to the volume of parts