Tuning Holley 80551 (4160)

[saf]

Hello everyone.
So, I just got myself a new Holley 80551 (600cfm, 4-barrel, vacuum secondaries) carb for my 5.7 engine. After initial tuning the boat runs great in low rpm range, starts right up. WOT is very good too. The engine bogs down in the mid range. After reaching about 2500rpm RPMs stop increasing until the throttle is fully opened, then she opens up (I am guessing as secondaries open). I hear loud whistling sound as I bring throttle back to mid range (presumable secondaries closing). I understand the carb needs tuning. I am leaning towards increasing the main jets. Jerking the throttle a bit while at 2500rpm seems to give it a little boost (presumably due to accelerator pump) making me think that it wants more fuel. Does this sound right to you? Any tips for tuning a Holley?

 

[kenny nunez]

Is it a marine carburetor?

 

[Scott Danforth]

that 600 CFM carb will be a bit small for a 5.7 (considering they installed 600 CFM carbs on 4.3's and 715 CFM carbs on 5.7's)

to answer @kenny nunez , yes its a 600 CFM vac secondary 4160 marine carb

However you are most likely going lean base on what you are describing

best you can do with that small of a carb is the following:
about #70 primary jets, #88 secondary jets, lightest vac pot spring, and about a #35 power valve. if your carb doesnt have power valves, you have to bump the primary jets up by 6. you will be a bit rich in the mid range, however you should read your plugs

as a reference, the 715 CFM 4150 that VP installed on many 5.7's was a #72 primary, staged (#80 and #90) secondaries from the factory. When I changed to vortec heads and changed the cam, I was running #74 primaries and #90 secondaries to keep from going lean

 

[saf]

that 600 CFM carb will be a bit small for a 5.7 (considering they installed 600 CFM carbs on 4.3's and 715 CFM carbs on 5.7's)

to answer @kenny nunez , yes its a 600 CFM vac secondary 4160 marine carb

However you are most likely going lean base on what you are describing

best you can do with that small of a carb is the following:
about #70 primary jets, #88 secondary jets, lightest vac pot spring, and about a #35 power valve. if your carb doesnt have power valves, you have to bump the primary jets up by 6. you will be a bit rich in the mid range, however you should read your plugs

as a reference, the 715 CFM 4150 that VP installed on many 5.7's was a #72 primary, staged (#80 and #90) secondaries from the factory. When I changed to vortec heads and changed the cam, I was running #74 primaries and #90 secondaries to keep from going lean

Thank you @Scott Danforth ! This was extremely helpful, you saved me quite a bit of time/money/aggravation. Went to our local O'Riley autoparts and got a pair of #71 jets and #50 power valve (this is what they had in stock, ordered #35 power valve separately but it will only come in a week). Switched to #71 main jets first (from stock #63) - almost brought me there. Still had some hesitation before WOT due to lean condition (could hear backfire when coming off WOT). Switched to #50 power valve (from stock #25) - lean hesitation before WOT is gone. Still have small hesitation before WOT, I am guessing #50 is too reach. But the boat is perfectly drivable and feels great. Will switch to #35 power valve once it arrives, hopefully it will make it perfect.

 

[Scott Danforth]

read your plugs.... what is your secondary jets?

what is your spring color? should be the light white.

https://documents.holley.com/199r8219-3.pdf

 

[saf]

Thank you again @Scott Danforth - very interesting read. So, the idea is to open secondaries sooner to compensate for insufficient air flow that 600cfm carb provides, did I get it right? I looked up the stock configuration for 80551, it says the secondary spring color is RED. I guess it translates onto PINK listed in the document you attached. Which means I need to downgrade my secondary spring as well. I guess I'll be ordering WHITE springs now...

As for reading plugs, I just ordered a new set for this purpose. What is the best procedure to do the reading? I mean should I put in new plugs, go into 2500-3000rpm range for a while, stop quickly and examine the plugs? This sounds problematic in real setting, I need to find a place to anchor first, drop the anchor and only then I can kill the engine and remove plugs. On the other hand, if I go back to the dock wouldn't all the idling needed to get to the dock skew the reading? Any wisdom there?

Oh, and as for secondary jets, this carb does not have any.

 

[Scott Danforth]

Yes, tool along at 3500 RPM, cut throttle, key off and read plugs. I usually pull cylinders 1, 2, 7 and 8

If you are on a lake or in the ocean, no need to toss anchor. However if you are in a river, you may need to toss an anchor

 

[saf]

Yes, tool along at 3500 RPM, cut throttle, key off and read plugs. I usually pull cylinders 1, 2, 7 and 8

If you are on a lake or in the ocean, no need to toss anchor. However if you are in a river, you may need to toss an anchor

Looks like I need your wisdom again. So, replaced the stock secondaries spring (red) with the white one (the softest spring in the kit). Went out for a test run with new spark plugs and vacuum gauge connected. No appreciable difference. Still getting the "surge" at WOT (flat spot before WOT). The vacuum gauge readings are most curious though. It looks like I am getting ~7in of vacuum at 3000rpm. I noticed that the "surge" starts as the vacuum drops to ~5.5, which happens to be the number of the power valve I put in last time. I also recall that the "surge" was starting later (more throttle) with the stock 2.5 power valve. So, maybe the "surge" has nothing to do with secondaries opening but rather power valve supplying extra fuel, which, in turn, increases rpms that opens secondaries?

Plugs read lean (very light touch of brown) although I am not sure this reading is conclusive. I only ran for a mile or so @3000rpm before stopping and pulling the plugs (ran out of room in the little bay where I was doing the testing). Is this enough time for plugs to change color?

So... it looks like I have two options (that I see): 1. increase the power valve number so it opens sooner (I have 16in of vacuume @ idle in gear, suggesting that I need #7.5 power valve according to Holley standard guidelines); 2. increase the main jets (I am at #71 at this point). What should I do?

 

[Lou C]

I'm wondering if your vacuum secondaries are opening too soon....
see this:

 

[Scott Danforth]

If the vac secondaries are opening too soon, go heavier on the spring. However you should hear them opening. Should be about 3500 RPM with moderate load, or 2500 with heavy load. They will go whhhhaaaaaa when the open, and whistle when they are almost closed

I wouldnt go to a 7.5 power valve. 4.5 max. Holly "standard guidlines" are for a sedan on the road with an automatic trans. Not a boat. Tuning books on holley and demon carbs do help.

The 71 primaries are still a little low for my taste

Wish you had a 4150 to tune the 2ndary fueling

 

[saf]

So... I swapped a stiffer secondaries spring. The stock spring was medium, so, I went for the brown one (one step down from the stiffest). Big improvement! I got maybe another 1000 rpm of usable medium range. I still feel secondaries kick in but much later. There is still a "surge" though right before WOT. Should I go all the way to the black (stiffest) spring? Seems a bit excessive. Besides, looking at the chart, black spring starts opening secondaries almost at the same RPMs as brown, I guess it opens them slower.

Seems weird that 600cfm carb is so much off with stock tune. I had Edelbrock 1409 (also 600cfm) prior to this one, it worked fine in stock configuration.

I still have problems with spark plug reading. I went to #73 main jets, ran for several miles @3000rpm, still getting perfectly white plugs. Is it possible that #73 jets are still not enough? How soon should I see the color on plugs?

 

[jhande]

Years ago I ran a Holley 650 CFM single feed vacuum secondaries on a power built street/strip 350 cu.in.. I only had to fine tune it a little out of the box. Before we go any further I'm curious what your idle vacuum is?

 

[saf]

Years ago I ran a Holley 650 CFM single feed vacuum secondaries on a power built street/strip 350 cu.in.. I only had to fine tune it a little out of the box. Before we go any further I'm curious what your idle vacuum is?

The idle vacuum is 18in "neutral" and 16-17in in gear.

 

[jhande]

The idle vacuum is 18in "neutral" and 16-17in in gear.

I was able to get my idle vacuum up to 22 after adjusting the timing and dialing in the carb. Here's a bit of reading that might help.

Carb Class: 5 Basic Carb Tuning Tips

Quick Fuel Technology® (QFT™) ships carburetors only after they have been thoroughly run-tested and adjusted on a typical engine. Engine testing all carburetors prior to shipment ensures that when a new QFT™ carb is bolted on an engine, it will start, idle and perform up to the customer’s...

www.holley.com

Tuning Your Holley Carburetor Made Easy

The traditional Holley four-barrel carburetor is incredibly robust, and the inevitable problems often have more to do with poor tuning than anything else. We thought we'd address a few common driveability issues that never seem to go away.

www.motortrend.com

 

[saf]

I was able to get my idle vacuum up to 22 after adjusting the timing and dialing in the carb. Here's a bit of reading that might help.

Carb Class: 5 Basic Carb Tuning Tips

Quick Fuel Technology® (QFT™) ships carburetors only after they have been thoroughly run-tested and adjusted on a typical engine. Engine testing all carburetors prior to shipment ensures that when a new QFT™ carb is bolted on an engine, it will start, idle and perform up to the customer’s...

www.holley.com

Tuning Your Holley Carburetor Made Easy

The traditional Holley four-barrel carburetor is incredibly robust, and the inevitable problems often have more to do with poor tuning than anything else. We thought we'd address a few common driveability issues that never seem to go away.

www.motortrend.com

What was your idle RPM? Mine are set to 600. I see vacuum going up to 20in or higher (did not take exact measurement) ~ @800rpm as I give it just a bit of throttle.

 

[saf]

So, I've been thinking about my own question - why my new 600cfm Holley is so much off tune in stock configuration. Holley's answer to this: the carb is sized incorrectly. My choice of 600cfm was determined by the size of the carb I had prior - Edelbrock 1409 (600cfm). (Edelbrock was installed by a mechanic who worked on my engine a few years back). I went to calculate the proper carb size for my engine using online formulas, now I am even more confused. Max RPM for my engine is listed as 5000rpm (in reality I am only getting 4600 @ WOT). Plugging it into the "standard" formula I am getting 430cfm "street" and 550cfm "racing" suggested carb sizes. Either way 600cfm appears to be too big! This would explain the bad tune (for my engine) in stock configuration. An oversized carb would cause weaker vacuum requiring bigger jets and stiffer secondaries spring to restrict air flow - this is consistent with what I am seeing in tuning process. Ant yet, VP puts 715cfm carbs on this engine! Although I see some 5.7 models that had 450cfm factory carb. I am confused... Any thoughts?

 

[Lou C]

I am confused as well to an extent, my 4.3 was equipped with a 600 CFM Holley after the Quadrajet went out of production but larger engines like a 5.0 Ford V8 came with a 450 CFM. My original Quadrajet is also a 600 CFM. I have heard that the Qjet has this flexibility built into its design being a spread bore carb with small primaries and large secondaries. All the Holley marine carbs except the 4175 are square bore carbs.

 

[jhande]

What was your idle RPM? Mine are set to 600. I see vacuum going up to 20in or higher (did not take exact measurement) ~ @800rpm as I give it just a bit of throttle.

I cheated a bit, my cam profile recommended 1,200 RPM for idle. I felt that was to high so I set it to 800 RPM. Once my timing was properly set I also fine tuned it watching the vacuum gauge. Just a slight adjustment helped raise the vacuum.

Well the standard size calculator produced multiple sizes including a couple of 600 CFM's. Including one for a 6 cyl.

https://www.holley.com/products/fuel_systems/carburetors/marine_carburetors/parts/0-80492

 

[saf]

My final settings are: #71 main jets (going to #73 felt less crispy), #35 power valve (did not feel much difference to be honest between stock #25 and #35 but settled on #35 to be consistent with VP), BLACK secondaries spring. These settings give me nice crispy response all the way from idle to about 3000rpm. After 3000rpm she still responds to throttle but more sluggish. I still get a slight surge over the last 1000rpm to WOT as I hear secondaries making the swooshing sound. Looks like this is the best I can do with this carb - still not perfect. I managed to get my hands on another Holley. This one is 750cfm (model #9015-1) . I'll start another thread as I attempt getting better results tuning a bigger carb...

 

[saf]

This is a "sister" thread to my other thread on tuning a smaller (600cfm) Holley. After failing to reach perfection with tuning a 600cfm Holley (going on 5.7 stock engine) I got my hands on a bigger Holley (750cfm). Runs a bit better out of the box compare to the 600cfm Holley (out of the box). This 750cfm Holley comes with #76 main jets, #105 power valve and PLAIN secondaries spring (no secondary jets). One problem out of the gate is a bog down around 1500rpm. She almost stalls once I try increasing RMP above 1100. As I push the throttle further she responds and kicks in above 2000rpm. 2000-3000rpm feels fine and crisp. Then she bogs down again until ~3500rpm. Then secondaries kick in and there is a nice throttle response all the way to WOT (WOT is good as well).
Things I tried so far:
1. Going down on main jet size to #73 made things worse
2. Increasing the secondaries spring stiffness (to BROWN) did not cure the flat before WOT. The engine gets into a surging mode increasing-decresing RPMs (instead of a flat spot) as the secondaries start to open
3. Decreasing the secondaries spring stiffness (to YELLOW) also leads to oscillating RPMs before secondaries open. I am also getting backfiring (presumably from lean condition) at WOT

Again, any pointers/advise is very much welcome.