4150 Holley swap for 1409 Edelbrock on 454 PCM

Hi everyone !
I finally did a swap of my old Holley (4160 with vaccum secondary and secondary metering plate). As it has a bad idle, with black smoke and unburnt fuel coming from the exhaust, sparkplugs are black, and mixture screws are tightened at maximum. Hesitation at acceleration as well.

The Edelbrock 1409 started good, just had to tune the idle screw to go to 800rpm.
I put a fuel pressure regulator with a gauge. Initial setup was 4.5 PSI (the factory mecanical fuel pump gives 6.5 PSI), power pump at 2nd hole.
I run at 300ft over sea level, use 90 aki octane gasoline with 10% ethanol (E95 E10 as we name it here).

The idle is ok but as I push the accelerator slowly, it hesitate, sometimes it stalls, and has no power until I go on secondaries. At 20mph it keeps the speed ok.
When I push accelerator quick, it backfires from the carburetor and stalls !
I tried the 3 holes on the pump : 1st it "paffffff" from the carb and stalls, 2nd it "paffff" and keep running if I go slowly, 3rd it stalls.
Went to 5.5 psi on the fuel regulator : no change.
Ignition setup is 8°BTDC @ idle 800rpm (as mentioned in the 454 PCM manual)

The floats are tuned the right way with 7/16 drill bit (I had to ask for new floats to the ebay dealer as the carburetor came with leaking used floats !), ah did I miss the fact that it's a remanufactured carburetor, actually a #9909 from National Carburetors.

It seems that the primary system is too lean for this engine, am I right ?

Is there a difference if the floats are set higher ?

Maybe the mettering rod spring is not strong enough for this displacement engine causing too lean mixture with the 454 intake vaccum ?

National Carburetors propose the kit#1488
On the Edelbrock forum, they propose to go to 10°BTDC

Do you guys have any recommendation for my setup ?

Regards

Rebuild the OE Holley and stop trying to change the system with an unknown product.

Unknown product !!! Edelbrock !? Come on guys, any inspiration ?
Don't forget that we don't have same Relationship on fuel consumption here. It's twice the price than in the USA. If I can save 30% fuel with an intelligent carburetor, it's tons of money saved at the end of the season.
The Edelbrock has a Metering rod system that saves fuel when no big load is required by reducing the fuel mixture.

Anyway, I already rebuilt the Holley, and still no good performance.

I have never seen a Edelbrock carb on a boat but it sounds like an accelerator pump problem, not even sure that they use one but that is what your description sounds like.

You already have the Edelbrock so it is a little late, but the Mercruiser Quadrajet works very well on a 454.

By unknown I meant that the carb you have was never made for your Supra . Is it even a marine carb? When the engineers at PCM built your drive train they chose the Holley for a reason . I am a X GM tech and have worked on hundreds of Rochester carbs I know them well but in my boats I stick with Holley. I guess I'm too old and not smart enough to re engineer the boat you might be smarter and younger. I don't believe any carb will give you a 30 % increase in fuel economy. INO if you are looking for fuel economy you bought the wrong boat.

Quadrajet was my first thought, but it's a spread bore carb, and Holley/Edelbrock are square bore, means it's a direct fit replacement. A Q-jet needs a square bore/spread bore plate to fit. Many forums says that Q-Jet are difficult to get properly tuned.

Michael, no offence to you, I just try to get a better mileage. Holley was THE solution maybe because they are the simplest carbs to rebuild and they don't need many adjustments, like the metering rod we find in the Edelbrock.
Notice that my Holley doesn't have a spring on the vaccum secondary diaphragm, I don't know why. It has 1 bowl leaking, an unadjustable metering plate on secondary, useless mixture screws, hesitation on accelerations, black smoke, black spark plugs etc.

The 1409 is a marine carb. It's a 600cfm, and some people here already have it on a 454, with no issue. Mine is remanufactured and came with dead floats. I maybe should ship it back to the dealer, but as I'm in France, it will cost me more than finding why it doesn't run the way it should.

Actually my tired Holley drinks 30L/hour at wakeboard speed : 20MPH @ 2200rpm. Some here reports 18L/hour with the same configuration/boat/engine. It's 40% better. Even if I see an economy of 7-8L/hour, it's 400L less per year and 600€ economy (basing on 50h/year).

My experience with any store bought rebuilt carb has not been good. When they tear down the carbs they combine all the parts from many carbs together so you don't get the same parts put together again. When I was a GM dealer tech and I learned that every part that is used is there for a reason . As soon as you start changing things you may unknowingly effect something else. I think my brother put it best '' For every action there is a reaction'' It looks to me you changed a bad carb with a different bad carb . At this point I think you should just order a new carb or get a professional involved.

There is no such thing as a "bad carb."

There is a dirty carb and there is a broken carb and there is a carb that has the wrong pieces in it, or a carb that is tuned incorrectly.....

I have a 1409 on my 454 and it performs flawlessly. The previous owner is the one that bolted it on (to save gas) and I have no idea if it was straight out of the box or if he messed with it. I've never done anything to it except run gas through it. The edelbrock is easy to rebuild with a kit, but I'm not convinced that your problem is carb related.

Backfiring and paffffff sounds (to me at least) sound like timing problems. Edelbrock have good documents on their website as far as tuning -- but if the boat won't even run, you aren't quite to the tuning stage yet. Are you sure your distributor is on the right tooth on the oil pump? Are you sure that your spark plug wires are in the correct order? Are you sure your distributor is in good shape?

Hi Wotan, I was expecting your feeling on it, as I know you run the same carburetor.
I agreed about a bad or at least a badly tuned carb for another badly tuned carb.
Believe me I regret to didn't buy a new one but a remanufactured. But understand me, it was half the price of a brand new one.

I should ask for a refund and send it back to USA. Or maybe try to sold it here in France. I don't know yet, have to think about it.

The ignition seems ok. It's not factory, it's an electronic one. I will probably go for a new HV ignition distributor with new wires for next season, it will be a good start for a good tune of the carburetor.

For every good running modified engine there is a hundred good running stock engines. What I am saying is now that you have strayed from the original components you cant get any useful information here because your engine is no longer stock . You will have to keep trying things until you get it working. Wotan lucked out and didn't have any problem yet. But even he cant help much with your problem.