How to jet the carb 4150

[CatDaddyDrift]

Hello,

I’ve put a 650 DP 4150 Holley on my Nissan 4.5L v8. It runs drives well until I go over about 60% throttle. Then it spitters. I think I need larger main jets in the rear bowls. Not sure though. This engine makes about 300hp I’d guess. It feels a lot more torquey than with the EFI and definitely has better response.

Also does anyone know if the fuel screws are capable of closing off the idle circuit? Can I run them seated or do I have to be off a hair. I need probably 1-2 sizes down on the idle jets I know this for sure.

I’ve tuned 2 barrels but not 4.

[BOOT]

Novelty but not ideal https://www.youtube.com/watch?v=kNoqIKq57qA

[BOOT]

Do you have a regulator on it to drop the efi fuel pump psi down a lot?

[barnym17]

My first thought would be wrong power valve.

[CatDaddyDrift]

Novelty but not ideal https://www.youtube.com/watch?v=kNoqIKq57qA

Interesting indeed. That was pretty eye opening.
I was hoping to learn how to tune a carb better as I get ready for an American proper engine... might not be so.

Do you have a regulator on it to drop the efi fuel pump psi down a lot?

Yes just running a holley Red

[skinny z]

Hello,

I’ve put a 650 DP 4150 Holley on my Nissan 4.5L v8. It runs drives well until I go over about 60% throttle. Then it spitters. I think I need larger main jets in the rear bowls. Not sure though. This engine makes about 300hp I’d guess. It feels a lot more torquey than with the EFI and definitely has better response.

Also does anyone know if the fuel screws are capable of closing off the idle circuit? Can I run them seated or do I have to be off a hair. I need probably 1-2 sizes down on the idle jets I know this for sure.

I’ve tuned 2 barrels but not 4.

As with any carbureted build I've been involved in (and this is the 4150 platform in specific) the first things on the list are a vacuum gauge and a wide band O2 sensor with an AFR display. I've got those two permanently mounted in the cabin of the car and can reference them any time .
The idle, WOT, power valve (especially) and cruise tuning are all MUCH easier with those instruments.

[F-BIRD'88]

If that is a EFI intake manifold you will very likely need to rework the floor and runners entry of the plenum to be fuel (distribution, vapourization) friendly. "carb wet flow friendly)
Look up the stock carb jetting for thar carb holley list number.. Start tuning with jets 6 sizes bigger and work towards leaner jets while noting WOT performance and plug appearance. The AFR guage will warn yiu if you are getting too lean.. A nareow band type will do this just as good as a wideband type.
Yiur carb was designed to work with a functional PCV system. Do that.

Until you have modified the plenum floor of that efi intake. don't expect much.

[BOOT]

Part of the tuning problem is that intake is basically an Extra air gap like the TPI/carb intake in the vid and it doesn't appear your using a hood to add another few factors.

[V12MECH]

Boot is right about a regulator, looks like a Q45, running fuel pressure is 40 psi, dead heads at 70. ECM controls timing, spark , probably looking for injector pulse feed back , not to mention a tps signal, wonder how many codes are set. This will take a bit of sorting as the Brits say. Are you running a n aftermarket ECM?

[CatDaddyDrift]

Boot is right about a regulator, looks like a Q45, running fuel pressure is 40 psi, dead heads at 70. ECM controls timing, spark , probably looking for injector pulse feed back , not to mention a tps signal, wonder how many codes are set. This will take a bit of sorting as the Brits say. Are you running a n aftermarket ECM?

This is true it’s a Q45. Now it’s on a holley red. Not smart enough to look for feedback in this era.

The ecm defaults to a simple timing advance when the TPS is unplugged. I have it set to 28 degrees advanced at max right now.

(Probably about 40 codes set with injectors, mass air flow, knock sensors, coolant sensors unplugged, and the Cam Timing solenoids hot wired to the advanced position!)

Part of the tuning problem is that intake is basically an Extra air gap like the TPI/carb intake in the vid and it doesn't appear your using a hood to add another few factors.

That’s a good point about the hood also. I didn’t consider that but that’s definitely not helping. The weird air gap plenum is definitely the main issue after watching the video above about trying this on a Chevy TPI.


——-

I’m going to fabricate a simple sheet metal single plane manifold and go from there. No need to waste time on this weird intake.

[CatDaddyDrift]

Hello,

I’ve put a 650 DP 4150 Holley on my Nissan 4.5L v8. It runs drives well until I go over about 60% throttle. Then it spitters. I think I need larger main jets in the rear bowls. Not sure though. This engine makes about 300hp I’d guess. It feels a lot more torquey than with the EFI and definitely has better response.

Also does anyone know if the fuel screws are capable of closing off the idle circuit? Can I run them seated or do I have to be off a hair. I need probably 1-2 sizes down on the idle jets I know this for sure.

I’ve tuned 2 barrels but not 4.

As with any carbureted build I've been involved in (and this is the 4150 platform in specific) the first things on the list are a vacuum gauge and a wide band O2 sensor with an AFR display. I've got those two permanently mounted in the cabin of the car and can reference them any time .
The idle, WOT, power valve (especially) and cruise tuning are all MUCH easier with those instruments.

Thanks. I have a wideband I’ll install and pick up a vacuum gauge as well. Then get it dialed in once I build my new intake.

[CatDaddyDrift]

If that is a EFI intake manifold you will very likely need to rework the floor and runners entry of the plenum to be fuel (distribution, vapourization) friendly. "carb wet flow friendly)
Look up the stock carb jetting for thar carb holley list number.. Start tuning with jets 6 sizes bigger and work towards leaner jets while noting WOT performance and plug appearance. The AFR guage will warn yiu if you are getting too lean.. A nareow band type will do this just as good as a wideband type.
Yiur carb was designed to work with a functional PCV system. Do that.

Until you have modified the plenum floor of that efi intake. don't expect much.

The 4150 650DP is designed to use PCV? Connected to the air filter or what?

This manifold is definitely the main issue see above I’ll just make a new manifold.

[BOOT]

I’m going to fabricate a simple sheet metal single plane manifold and go from there. No need to waste time on this weird intake.

You could make the efi intake work ok, with a lot of tweaking but it'd still be far from a sheet metal intake done right. That efi intake plenum is prob to big for a carbs booster signal with also bad distribution anyways.

I have no clue bout that engine but judging from the pics your gonna end up with much longer outer and short inner runners with a single plane. More than normal on other V8's, good/bad depending on what you want. If your gonna go to the trouble, I'd almost fab two separate intakes, think tunnel ram. your gonna have less turns/angle on the runners going to two separate plenums. I think that'd be pretty cool and work good as well. I'm not a intake design guru but there are people on here who would have invaluable input, so if your gonna go that route start another thread and ask for some opinions.

Single plane I'd try a bit taller with a small plenum. Dual carbs, you could place the plenums where it makes all runner equal(kinda have to tah fit two carbs) and I'd also go taller to have a straighter shot but ask someone to give you ideal runner size specs or buy pipemax

Also plenty of people use carbs w/o a hood, it's just something else to effect your tune and that efi intake is already not ideal.

Stuff like this makes me wish I had a tig, be a cool project GL!

[BOOT]

I mean you could prob cut up a stock intake or two to help fab the dual quad intakes, just sorta rotate and reweld some of the runners. Give you a chance to texture them all nicely.

[1980RS]

Disconnect the sec side link arm and run it on the pri side only at WOT and see how it acts, if ok above 60% then either it's too fat or too much carburetor for that engine. Most Holley DP I have used have been a little fat out of the box and QF's are worse.