Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor
Tuning for a mopar 318
omaha:
I have a 318 in my 1980 Power Wagon. It has a Q jet from a 1985 Dodge van, 3/4 ton. It also has the 360 heads and the factory intake from the dodge van. this can be a very good combination. I can get up to 18 mpg if I keep it at 60 mph or less. Check your intake adaptor. As far as I know the performer Rpm has the square pattern and you need to be careful that this are is sealed up good and does not have any vacuum leaks in this area. That is it, I cant come up with anything more other than 318's are notoriously "cold natured" engines. ( a good working choke is essential) You cant "get on it" until it is warmed up and this takes a while with a 318. By the way, I think with the magnum style heads you should be able to achieve more power and more fuel mileage.
toocheaptosmoke:
You're right about the rpm intake being the square pattern, I have an edelbrock adapter plate in there which has a bigger mounting surface than the other generic adaptor plates.
I went back to the 73 main jets, and double checked other stuff in the carb. Float level at 1/4", spring hangers look good, power piston moves freely. I drove it and the bog is back pretty bad, but it only happens when you apply throttle. For example, say you're cruising in 4th gear at 2000 rpm. Give it some throttle, bogs for a second, then she comes back to life and takes off. The power is better now than with the larger jets, but the off idle lean spot is worse. I think it may be a problem with the power piston not having enough spring, this could be causing a lean spot off idle if it is taking too long to raise the primary metering rods? I used a straw to "feel" the power piston while revving the engine, it never budges from fully seated. I already have the heaviest spring I got in there, but just ordered a kit from Cliff's to try a heavier one.
toocheaptosmoke:
I received the spring kit, and it looks like none of the springs were any heavier than the one I was already running. As a last resort I took one of the old springs I had and stretched it out, it put quite a bit of preload onto the power piston. After installing that spring I also was finally able to feel the power piston rise (using a straw) while cracking the throttle, this was the first time it has ever done that. Initial test runs showed a greatly reduced bog, sometimes almost no hesitation at all. After a few miles the bog started to return a bit, which I think may be from the spring taking a set back towards its original length. I don't have a vacuum gauge, but I may try to get one just to see how much vacuum this engine is pulling at idle and cruise.
Also, I've ran the accelerator pump on both settings throughout the tests, it never really makes a noticeable difference what position it's in.
Cliff Ruggles:
The dark blue spring in our kit is really strong, and will pick the piston up quickly. I'm still not sure why your set-up is wanting so much fuel from the main system right to start with? Did you verify that all the main airbleeds are in place and what size are they?......Cliff
toocheaptosmoke:
Next time I work on the carb I'll try the blue spring. I have never measured the airbleeds, if I remember right I just visually compared them to make sure they weren't the large size. (should have kept better notes along the way) Here's a picture comparing the old primary rods to the .044 ones, I think you can see the air bleeds pretty decent.
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