Carburetor modification
 

I drive 400 miles to work on rural roads every Monday in temperatures varying from -5 to 40c. I need more mid range power for overtaking trucks, and thought a carburetor change/modification would help. The car, a 1984 convertible, is standard apart from a better manifold and exhaust.

It was suggested having bigger jets in the standard carby with a better air filter such as a Racing Beat version would be a simple solution. Any advice would be appreciated.

Install a K&N filter element, run some sort of ducting from the front of the car to the airbox for cold air intake, convert the secondaries to mechanical and then have the car dynoed and the carb re-jetted if necessary. Other than that there's not much more that can be done to the stock carb unless you wanna spend big dollars and for a stock motor it's probably not worth it.

carb mods
 

Revhed has a good idea!, the cold air ram is effective. Some holes in the top of the air box outside of the filter is also helpful. If you check for vaccum in the air cleaner at full throttle in most cases you will find that the ram helps but there is still vacuum in the air cleaner. The holes will help further. The stock snorkle is too small. It is easier to drill some holes(than make a snorkel for most people) and use a 6" duct. The "leftover" duct air should be directed over the top of the air cleaner to get this cold air (12deg drop in air temp = 1% power gain) to the drilled holes. Since you are "on the fly" if you don't have a light fly. think about it. It frees up torque during accl. that would "go into" the flywheel, to the rear tires. If you don't have a lot of hills to start on I use the aluminum. What rear end gears are you running? Remember to balance getting more torque with having to turn more rpm's/road speed. Rob

I've been playing around a bit, and discovered a simple mod that can work wonders.
First of all, you can eliminate the vacuum operated secondaries, and wire the linkage together so that the secondaries are mechanical. It's a real ass-kicker. (If you take the vacuum diaphragm box off, be sure to close up the vacuum hole. It should'nt cause a "vacuum leak", but can allow dirt in because it's unfiltered.)
But what I've done with good results, is to enlarge the volume of the accellerator pump by adding several gaskets to the housing, along with longer screws. (Two or three gaskets on each side of the diaphragm. Pull the spring a little longer as well.)
Then, most importantly to get the best result, I attached a small extention to the bottom of the piston lever so that it's about one inch longer. (Basically this is a 1 1/4 inch long strip of metal with a hole at either end. Bolt it to the hole that the linkage arm normally goes through, and then the bottom hole may have to be made oval with a chainsaw file. The bottom will also have to be bent slightly to make a perpedicular contact when the linkage arm is put through it. Pull the linikage arm spring a little longer.)
What normally happens is that the pump shot finishes long before the primaries are fully open. What is ideal with mechanical secondaries, is that there is more of a pump shot, over a longer duration.
With this modification, I now have an accelerator pump shot that is very strong, and lasts the entire opening duration of the secondaries, as well, due to the longer arc.

If anyone is interested in trying this, you can drop mail in my box here.
I only know of one other person who's tried this per my instructions, and he's having other problems, so he can't say if he's happy with it or not yet. But the best thing aside of this costing zero bucks, is that it can all be "undone" with no harm to the carb.

carb mods
 

Converting the carb to mechanical secondaries works great at the track, and for some hardcores. The usual complaint I hear is about flat spots. I just fixed one 2 days ago. Something to consider, this is written in most carb performance books I've ever read, it goes something like this: If you can feel the vacuum secondaries "come in", it usually means they have opened to early or late. You had the hp already dropping off, then it comes back. This is the power boost you feel, it is actually a loss of power, followed by getting it back, plus some(from the additional air/fuel). Check it out next time you are on the dyno! If you want to play with the top end with a small flat spot at the begining of the secondaries, you can have the secondary venturis(removable in the 12a)bored out and rejet the secondaries richer to balance the decrease in vacuum the jets will see from the bigger venturies. Rob

I feel the secondaries "come in" but there's no flat spot, the car just pulls even harder. (and breaks the tires loose in the rain in 3rd gear... :eek: )

I just don't use a spring, wiring it together is overkill IMO.