5.7 vortec pertronix and Holley big carbs timing

[QBhoy]

Hi guys…
Something I know little about and less again, with this ignition system being pertronix…less further with a big Holley tuneable carb !
What are the general thoughts on timing settings on these ? A good friend has a pair of repower 2015 350 vortec engines with petronix ignition and Holly’s. The starboard engine seems to run well with around 9 degrees btc at about 800 rpm. But the other isn’t happy really. Would someone mind telling us what we should be aiming for at what rpm settings ?
Much appreciated and thanks in advance. Info on it isn’t easily available, or if it is…quite ambiguous, as far as I can tell.
Cheers.
Allan.

 

[Scott06]

Hi guys…
Something I know little about and less again, with this ignition system being pertronix…less further with a big Holley tuneable carb !
What are the general thoughts on timing settings on these ? A good friend has a pair of repower 2015 350 vortec engines with petronix ignition and Holly’s. The starboard engine seems to run well with around 9 degrees btc at about 800 rpm. But the other isn’t happy really. Would someone mind telling us what we should be aiming for at what rpm settings ?
Much appreciated and thanks in advance. Info on it isn’t easily available, or if it is…quite ambiguous, as far as I can tell.
Cheers.
Allan.

My vortec lives really with 10 degrees initial total is in low 30s, this is with a TBV ignition. total is in by 2800 or 3 k if i recall.

assume you have done compression checks and plug readings ? Try swapping carbs or pertornix engine to engine

 

[Scott Danforth]

What is the advance curve? Total advance?
Is it knee shaped or linear?

Stock motor? Modified
Cam duration? Lift? Rocker ratio?

What intake? Single plane, dual plane? air gapped?

What size carb? Series? List number?

Primary jets, secondary jets, power valve size?

Carb spacer?

My slightly modded 5.7 SBC with a 264 degree duration cam, ported vortec heads, dual plane port-matched intake, 1" carb spacer, Holley 715 vac secondary 4150 with 78 primary jets, 92 secondary, #45 power valve on primary ran best at 12 BTDC, 24 degrees of advance, linear ( no knee )

It was a tad fat (rich) between 950 and 1200 rpm

 

[QBhoy]

What is the advance curve? Total advance?
Is it knee shaped or linear?

Stock motor? Modified
Cam duration? Lift? Rocker ratio?

What intake? Single plane, dual plane? air gapped?

What size carb? Series? List number?

Primary jets, secondary jets, power valve size?

Carb spacer?

My slightly modded 5.7 SBC with a 264 degree duration cam, ported vortec heads, dual plane port-matched intake, 1" carb spacer, Holley 715 vac secondary 4150 with 78 primary jets, 92 secondary, #45 power valve on primary ran best at 12 BTDC, 24 degrees of advance, linear ( no knee )

It was a tad fat (rich) between 950 and 1200 rpm

Thanks Scott It’s a standard repower marine vortec 350. But with the Holley carbs. Good info. No idea on the other stuff to be honest.

 

[QBhoy]

What is the advance curve? Total advance?
Is it knee shaped or linear?

Stock motor? Modified
Cam duration? Lift? Rocker ratio?

What intake? Single plane, dual plane? air gapped?

What size carb? Series? List number?

Primary jets, secondary jets, power valve size?

Carb spacer?

My slightly modded 5.7 SBC with a 264 degree duration cam, ported vortec heads, dual plane port-matched intake, 1" carb spacer, Holley 715 vac secondary 4150 with 78 primary jets, 92 secondary, #45 power valve on primary ran best at 12 BTDC, 24 degrees of advance, linear ( no knee )

It was a tad fat (rich) between 950 and 1200 rpm

Thanks Scott. Standard 350 repower engine with big 4 Holley cabs. One engine runs great. The other seems to be lazy getting past 1800-2000 rpm (right about when the back two open). Can occasionally stall at idle going into gear.

 

[stresspoint]

remove the fuel line and pull out the fuel filer , its probably gummed up , FWIW i usually take them out and chuck them to spare parts.

 

[jimmbo]

Big Holley Carb, really don't say much. But a 5.7 turning 5000rpm, with a VE of 80% is only gonna need about 430cfm. So a 600cfm is more than enough, anything bigger is just a waste and the Primaries too big and that can lead to poor Off Idle response.
Are both Carbs you have the same Part #? Are both jetted the Same, same Accelerator Pump Cams and Settings? If Vacuum Secondaries, do both have the same Springs in the Diaphragm housing? If there is a Stumble when the Secondaries are opening, it is usually cause they are opening too soon. If the carb is a Double Pumper(mechanical Secondaries), then it is likely the Accelerator Pump circuit for that side is not functioning correctly
Also, most Holleyes have an adjustable Idle Stop on the Secondaries(it is there to provide a means of setting the Primary Throttle Plates in the proper location in relation to the Idle and Idle Transfer Slot, and provide enough Air for the engine to run, when wild Camshafts are used), are both set the same?

 

[Scott Danforth]

Thanks Scott. Standard 350 repower engine with big 4 Holley cabs. One engine runs great. The other seems to be lazy getting past 1800-2000 rpm (right about when the back two open). Can occasionally stall at idle going into gear.

Standard 350 doesn't mean anything

Flat-top pistons? Dishes pistons? Heads?
Cam?
Rocker ratio?

If it's a generic 350, it's flat top pistons, 220 ish duration cam with less than 0.40" lift

All Holley 4150 carbs are physically the same dimensions externally. By Big, are you talking 500CFM or 1050CFM?

A generic 350 will only need a 600-650 CFM max

Define getting lazy? You mention when the back two open. Is this a mechanical secondary carb?

To second Jimbo, are both carbs not only the same list number, however set up the same? Are both motors identical? (Because if they are generic ramans, they may not be)

 

[QBhoy]

Big Holley Carb, really don't say much. But a 5.7 turning 5000rpm, with a VE of 80% is only gonna need about 430cfm. So a 600cfm is more than enough, anything bigger is just a waste and the Primaries too big and that can lead to poor Off Idle response.
Are both Carbs you have the same Part #? Are both jetted the Same, same Accelerator Pump Cams and Settings? If Vacuum Secondaries, do both have the same Springs in the Diaphragm housing? If there is a Stumble when the Secondaries are opening, it is usually cause they are opening too soon. If the carb is a Double Pumper(mechanical Secondaries), then it is likely the Accelerator Pump circuit for that side is not functioning correctly
Also, most Holleyes have an adjustable Idle Stop on the Secondaries(it is there to provide a means of setting the Primary Throttle Plates in the proper location in relation to the Idle and Idle Transfer Slot, and provide enough Air for the engine to run, when wild Camshafts are used), are both set the same?

Hi.
They are Holley 4150 600cfm. Both identical parts.
Engines are the usual vortec 5.7 you get here to replace old engines with, if needed. In this case, it’s twin 350 vortec rated at 4600-5000 I’m sure. Standard cam and all the rest. But with the delco ignition thrown out and petronix fitted instead. Carbs have been set up fairly well, after much tinkering with the valves and feeler gauges, as far as I know. But one of the engines doesn’t quite like the change over stage for a few seconds when accelerating…but afterwards will push through and produce enormous power. Enough to push a heavy classic princess 286 to around 50 mph through VP290dps turning B5 props to the top of the rpms or close.
Just that occasionally one engine will bog and be a little rich at idle or when slowing down.
Just heard from the owner that the timing at the top end hasn’t been set we think. Only been set at about 809 rpm and at 9 degrees at that.

 

[QBhoy]

Standard 350 doesn't mean anything

Flat-top pistons? Dishes pistons? Heads?
Cam?
Rocker ratio?

If it's a generic 350, it's flat top pistons, 220 ish duration cam with less than 0.40" lift

All Holley 4150 carbs are physically the same dimensions externally. By Big, are you talking 500CFM or 1050CFM?

A generic 350 will only need a 600-650 CFM max

Define getting lazy? You mention when the back two open. Is this a mechanical secondary carb?

To second Jimbo, are both carbs not only the same list number, however set up the same? Are both motors identical? (Because if they are generic ramans, they may not be)

Hi Scott. Just realised it was yourself. Yeah, see reply to Jimmbo there. Excuse the ignorance. I think the owner is signing up as we speak. He has endlessly bed time perused the Holley manual recently and knows the carbs inwards fairly well by now. But just very close but not quite there yet. Not ruling out any electrical gremlins being responsible just yet though.

 

[Scott06]

Hi.
They are Holley 4150 600cfm. Both identical parts.
Engines are the usual vortec 5.7 you get here to replace old engines with, if needed. In this case, it’s twin 350 vortec rated at 4600-5000 I’m sure. Standard cam and all the rest. But with the delco ignition thrown out and petronix fitted instead. Carbs have been set up fairly well, after much tinkering with the valves and feeler gauges, as far as I know. But one of the engines doesn’t quite like the change over stage for a few seconds when accelerating…but afterwards will push through and produce enormous power. Enough to push a heavy classic princess 286 to around 50 mph through VP290dps turning B5 props to the top of the rpms or close.
Just that occasionally one engine will bog and be a little rich at idle or when slowing down.
Just heard from the owner that the timing at the top end hasn’t been set we think. Only been set at about 809 rpm and at 9 degrees at that.

Would make sure timing is ok should be 10 btdc at idle rest sounds like a carb or fuel pressure issue

 

[QBhoy]

Ok. Just heard back again from him. He has set the timing further up it turns out. His words below
“Had a wee read there… i both engines timed to 9deg with medium springs in the pertronix giving 24deg at 3k with a total timing of 33 deg. “

 

[QBhoy]

Would make sure timing is ok should be 10 btdc at idle rest sounds like a carb or fuel pressure issue

Thanks Scott. Fuel pressure is known as good. Gauges in line recently fitted and showing well.

 

[QBhoy]

Would make sure timing is ok should be 10 btdc at idle rest sounds like a carb or fuel pressure issue

Scott. Would you be setting them to 10o literally at idle speed ? And in gear and warmed up or not loaded up and warmed up ?

 

[Beatman19801]

Hi fellas. It’s my boat… thanks for the information. They are pertronix distributers set to 9deg btdc and medium springs giving 24deg advance at 3k odd with a total timing of 33deg. The issue is at approx 2800r there is a flat spot on one engine. She’s fine if you push through it. Would it be the spring in the vaccum secondary’s that would need a look?

 

[QBhoy]

Hi fellas. It’s my boat… thanks for the information. They are pertronix distributers set to 9deg btdc and medium springs giving 24deg advance at 3k odd with a total timing of 33deg. The issue is at approx 2800r there is a flat spot on one engine. She’s fine if you push through it. Would it be the spring in the vaccum secondary’s that would need a look?

Ah. Higher up the rpms than I thought. Apologies for the info earlier. Good to see you joining up Stephen. You won’t get too much better than these guys currently responding now.

 

[Scott06]

Scott. Would you be setting them to 10o literally at idle speed ? And in gear and warmed up or not loaded up and warmed up ?

Warmed up in neutral is where I’ve set mine . This is the merc TB V vortec spec in base mode when you take it out of base just like the Delco est they are adding more advance at idle maybe 15-16 or so

What’s the total advance

When u say it is rich sometimes wonder if float bowl is over flowing needle seat or too much fuel
Pressure. What do plugs look like at idle


If they look ok and fuel level in bowl is ok would look at accelerator pump especially any slop in the linkage. Had that on my Eddy carb slight delay in pump shot due to linkage slop … took the boat a long time to recover under holeshot. Didn’t see how lean it was after stabbing fasa until I put AFR on it

 

[jimmbo]

What is the part # of the Carbs? It would be on the Air Horn.
Do both carbs have the same Spring in the Vacuum Control. Holley makes several, and they will change the Rpm the Secondaries start to open, and how quickly they open. All Holleys, have Idle and Off Idle Circuits on the Secondary Side. This is to insure the Fuel in the Bowl is Fresh. Any Dirt/Gum/Varnish in these Circuits can cause Issues. Of course so can a Vacuum Leak, due to a leaky Gasket(s).
The big Question, is; Have these carbs been modified from Factory Calibration?
Holley Accelerator Pumps on these is easy to set. Just make sure that at WOT, there is still a bit more Movement(about 0.025") available for the Lever that pushes on the Diaphragm, other wise that Lever will get bent. However, by 2800, the Fuel will, or should be flowing solidly from the Main Venturi Nozzle, so the Accelerator Pump is not likely the Issue.
I would be pulling both Fuel Bowls off, as well as the Metering Blocks(a 4150 has Metering Blocks with replaceable Jets, some Secondary Blocks even have Idle Mixture Screws. However, a 4160 uses a Metering Plate with no provision for Jet Changes. Different Plates with various Main Jetting and Various Idle Jetting are available), for inspection and Cleaning. it also allows for Verification of the Metering Jets and Power Valve. A lot of People mistake a 4160 for a 4150, as they, at a glace don't really look much different.

 

[Scott Danforth]

Hi fellas. It’s my boat… thanks for the information. They are pertronix distributers set to 9deg btdc and medium springs giving 24deg advance at 3k odd with a total timing of 33deg. The issue is at approx 2800r there is a flat spot on one engine. She’s fine if you push through it. Would it be the spring in the vaccum secondary’s that would need a look?

Read the thread

Identify your motor. Very specifically identify the combustion mix of bore, stroke, piston style, heads, rocker ratio, cam duration, etc

Identify your carb. Specifically the air horn numbers and any mods done

Report it all back here

 

[flashback]

Swap the carbs and see if the gremlin follows.