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I have a 73 Mustang with a 70K mile 351C-4V motor (stock long block). Edelbrock 600 cfm VS carb and Performer intake. Factory exhaust manifolds, dual exhaust, Unilite distributor. C6 with a low gear kit and 2800 stall converter, 3.89 gears.

I've always had a problem with a "bog" on acceleration, which is not surprising considering the huge ports on the 4V Cleveland. Setting the initial timing to 12 degrees helped some. So did the looser converter (2800 stall).

The Edelbrock was a 1405, stock right out of the box. I decided to try tuning it a little bit. First I moved the accelerator pump linkage to the hole closest to the carb body. This gave me an earlier pump shot upon acceleration. That helped a little bit.

Then I bought a Step-Up spring kit (Edelbrock #1464 about $6). The step-up spring controls when the metering rods go from "cruise" mode to "power" mode. The carb is delivered with a 5" (Hg) step-up spring. I wanted the carb to go to power mode EARLIER, so I installed a STRONGER step-up spring (the pink one, 7" Hg). This made a definite difference, but there was still a slight bog under certain throttle conditions. Next I went to the 8" spring (strongest one in the kit). WOW, bog gone and some wheelspin off the line. This car would not spin its tires before--now it will.

I think the carb's a little rich in cruising mode, so I'm going to experiment with the metering rods next to try to lean out the cruising mode. I'm also going to try richening the power mode a little more to see if it makes a difference. Edelbrock makes a whole assortment of metering rods with various cruising/power mode combos, so you don't have to change the jets unless your carb is way off. Just get the right metering rod. Look on the Edelbrock website to see which springs, metering rods and jets your carb came with (different between 1405 and 1406). The bigger the metering rod diameter, the leaner the carb gets. For example, my factory metering rod is .070 cruising and .047 power. If I change to a .073 x .047 the cruising mode is leaner but the power mode is unaffected. For a richer power mode I would go to a .070 x .042.

If you have an Edelbrock carb and are having a bogging problem, I strongly recommend you try this. It is ridiculously easy to change the step-up springs and metering rods. Takes about 60 seconds (I'm not kidding) and you do it with the carb on the engine. Just don't drop anything down the carb while doing it. Changing the jets is a little harder - you have to remove the top of the carb.

I would like to thank Hemikiller. In a previous post he suggested changing the step-up springs. That's what got me started on this.

 

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I still have the stock cam, which AFAIK is rated at 204/214 with .480 lift. I also still have the stock valve train (with 70K miles on it) which is why I don't rev the motor much above 5000 rpm anyway (don't want the head of a valve bouncing around in the combustion chamber).

I have a whole other set of heads with one-piece valve, studs, stronger springs, roller rockers, a more aggressive cam and headers all waiting to go on it, which is part of the reason why I went to a 2800 stall converter. Obviously I'll be able to rev the motor higher with those pieces and the higher stall won't limit me as badly.

That being said, I've had this car for 15 years and as the motor was pretty solid I didn't want to make major changes to it. As a result I've been trying to get the best driveability/performance out of the basically stock motor that I could. I just listed the items that helped me achieve that goal. I know that there are some people out there with a basically stock 4V Cleveland that want as much performance as they can get without having to "get into the motor". Once you start upgrading the cam you really need better valves and better springs and better rockers and so on and so forth and the next thing you know you've got another 2 grand into the top end of the motor. That's great for the people ready to take the next step in making more power with a Cleveland (like I am) but I figured some people just want to do the best they can with what they already have and that they could benefit from my experiences. The truth of the matter is that the 2800 stall converter did more for seat-of-the-pants performance than any other single thing I did, even if it did "narrow" my rpm range.