Vortec with Quadrajet question

[gbracer08]

Switched to new vortec engines from a 270 Crusader. Setup is the same on the vortec but the engine burns more fuel. The carb primary have not been changed. Do the vortecs need leaner primary rods on the Quadrajet. Both engines run identical in terms of fuel flow and burn more than the non vortec counterparts. Ignition are est.

 

[Scott Danforth]

You need to tune the carb for the new motor

 

[gbracer08]

I’m trying to understand how much I should lean things out. Plug shows rich. It has 70/43 primary and wa thinking of going to 45 rods but looking to see if anyone has retuned the carb so I can get a better starting point

 

[Lou C]

Is the carb that's on it original to the original engine?
Given the fact that the Vortec heads flow more air, I'd expect the original carb from the pre-Vortec engine to run leaner but that's not what you are finding.
Any Quadrajets that are sold by the big "reman" outfits, can't be relied on to be set up right at all, that's why I'm asking.
The one on my engine is actually the OEM carb, un-modified, just cleaned out and rebuilt with better quality parts and the plugs color wise are pretty much the way they should be.
Running rich can also be caused by typical carb issues that a good rebuild will take care of (clogged air bleeds, float too high, leaky needle valve, etc). I would go through it and make sure all that is good (pay attention to the idle air tubes) before changing jetting/rods

 

[gbracer08]

The carbs have been rebuilt with all proper parts. The original cl secondary rods and the primary jets and rods are the same. They ran fine on the other engines. They are original Quadrajet carbs.

 

[Lou C]

https://www.florida4x4.com/tech/quadrajet/qjtshoot.pdf

probably more than you want to know, but the guy who wrote it is one of the Q-Jet gurus, along with Cliff Ruggles.

 

[Scott Danforth]

Are the welsh plugs leaking?

 

[gbracer08]

No leaks on the plugs. All sealed up

 

[Lou C]

Did you replace the fuel pumps? Ever check the fuel pressure? Higher than normal fuel pressure (over 7 psi for a Quadrajet) can overcome the needle and seat and force fuel into the bowl, causing higher than normal fuel level.
All Vortec engines have electric pumps, the older pre-Vortec engines used mechanical pumps, but switched to electric after 92/93? Rich running could also be a float that's set too high, or clogged air bleeds, even a really dirty flame arrestor can cause it to an extent. It just doesn't make sense that changing to an engine with Vortec cyl heads will cause it to run richer if nothing else changed.

 

[gbracer08]

I can check the fuel pumps. Only thing is how to hook one up from the pump to the carb. The line is all one piece. I guess I would have to fabricate a new one.

 

[Lou C]

I disconnected the steel line from the pump to the carb and made up a rubber line with the right size barbed fittings and put the fuel pressure gauge in the center of that line. That gives a more accurate reading than dead heading the pump.
Also just thought of something else, what did you do for the auto chokes?
Pre-Vortec uses a well type (divorced) choke with the spring heated by the exhaust crossover in the intake manifold.
Vortec has no exhaust crossover in the intake manifold.
The only auto choke set up that will work on these is electric, and I don't think the marine Quadrajets were easy to convert to electric....

 

[gbracer08]

I have an electric choke kit installed from a vendor. Pain to install but works well. @Lou C how did you attach it back to the pump and the metal line. Were you able to get barbed fittings with the proper ends to mate with the metal pipe.

 

[Lou C]

What I did was remove the metal fuel line at both the pump & carb (use a line wrench so you don't round off the hex fittings) and took it to a speed shop. I got barbed fittings matched up with the same thread to thread into the fuel pump and the carb and used 3/8ths rubber line with the pressure gauge in the center of it. So, the rubber line with the pressure gauge takes the place of the metal line just for pressure testing. Then you reinstall your original metal line. I always wanted a way to check fuel pressure because a lot of people have had problems with carbed engines due to fuel pumps putting out too much pressure.
When I tested my mechanical pump, I got 5.5 psi which is fine for the Q-Jet.
So, you got electric chokes which is good, are you sure they are opening?
The way they work, unless there is a constant 12V source and a good ground, they will close. The default position is closed, unless 12V is connected.

 

[gbracer08]

Thanks, I can make a new line by buying the ends i currently have that go into fuel line. Choke is open, heats up pretty quick and opens and stays open once engine is warm.

 

[Lou C]

Sounds good post up your results glad the electric chokes work properly. The will definitely open faster than the old manifold heated chokes.