Carburetor swap out, what adjustments are necessary?

[ryno1234]

I've had nothing but issues with my Rochester Quadrajet and cannot find a local boat shop that will work on my boat because its too old (early 90's).

After buying several reman's and having nothing but issues with each, I decided to purchase an Edelbrock 1409 (https://www.summitracing.com/parts/...MI7qyp0pLw6wIVwB-tBh06NA0TEAQYASABEgLbX_D_BwE)

I have a low performance GM 305 (~200 HP if I recall correctly). The Quadrajet has huge CFM (750+) and this Edelbrock is 600. From what I understand, 750+ CFM is way too much and 600 should be more than enough and then some.

My question is, can I simply bolt up this new carb, adjust the idle and it will be "good"? What tuning is necessary for basic reliable operation? I'm hoping the carb simply works out of the box with basic idle adjustments.

 

[Rick Stephens]

I found the process to be fun, but definitely has a learning curve and requires some patience. I *think* the 1409 ships calibrated for the Vortec 5.0L. But that is an assumption based on looking at the installed jets, needles and springs on the one I purchased. No matter what though, if you want your motor to run like it should, and want to avoid the possibilities of either burning a bunch too much fuel or being too lean and burning a hole in a piston, you will need to calibrate to your own motor. That process can be as painful as your personality makes of it. Or fun, which is somewhat in line with my personality.

First step is to read the manuals, you can access online or I think one comes with the carburetor. You need to understand how the carburetor works through out the range of throttle plate openings and produced vacuum. Understanding things like the somewhat reverse logic of stronger needle springs mean more fuel provided, make it fairly easy to tune. You need to start at idle, work your way up through midrange throttle and end with secondary jet mixtures. It takes buying parts to make changes. You can get those all over, I bought mine mostly through Summit Racing online site.

The 1409 is the easiest carburetor made to work on. There is quite a lot of experience with them on this forum and a lot of quality assistance when you get stuck trying to figure out what you are experiencing.

Rick

 

[nola mike]

Ya know what I was thinking, Rick Stephens ? I wonder if this carb *is* tuned out of the box for a non-vortec 5.0...That would mean that HP wise it's probably also close to the 4.3L vortec?

 

[Rick Stephens]

Ya know what I was thinking, Rick Stephens ? I wonder if this carb *is* tuned out of the box for a non-vortec 5.0...That would mean that HP wise it's probably also close to the 4.3L vortec?

I get where you're trying to go. But if we did everything to the 5.0L that are done to make a high end 4.3L Vortec, the 5.0L would be up over 250 HP. I rather prefer the 4.3 in my smaller boat for its efficiency. But nothing wrong with the 5.0 for a bit bigger barge. More torque definitely has its place.

I think ryno1234 is going to like the results if he puts the time into calibration. He may even luck out and be close out of the box. If anything, your experiences and others lately have made me doubt the one size calibration fits all opinion I had.

 

[nola mike]

If anything, your experiences and others lately have made me doubt the one size calibration fits all opinion I had.

...But I don't know why it shouldn't be 1 size fits all. It's the same damn engine. You think mercruiser custom tunes each carb that ships with their engines? I would still love to find out the stock settings on the webers...

 

[Rick Stephens]

I believe the stock Weber for the 4.3LX came with .080 primary and .089 secondary jets.

 

[nola mike]

I believe the stock Weber for the 4.3LX came with .080 primary and .089 secondary jets.

That's not the vortec though, right?

 

[Scott06]

I think it will be reasonably well set up for a non vortex 5.0. I ended up changing out to a bigger accelerator pump nozzle but otherwise I was pleasantly surprised how well it did out of the box.

and yes 600 cfm is better sized for a 5.0 than a 750, but both the q jet and edlebrock use a secondary air flap that opens based of engine demand, essentially vacuum secondaries. This is what allows the to be used on such a wide range of engine displacements.

you may need a square to spread bore adapter, different throttle bracket if bolt spacing is different, and modify the fuel line