Well, it’s that time again… Time to get that old Keihin dialed in for smog testing.
If you’re super lucky maybe you even have a bitchin set of sidedraft Mikunis that howl like an angry wolf on fire. If you live in a state (Or country) that doesn’t do smog testing then you’re in luck, and having an aftermarket carb is simply a matter of choice. That being said, the Keihins used in most early European and JDM models were a bit simpler to work on and lent themselves to easier tuning (Relatively speaking of course). The 3 barrel octopus under MY hood however is a finicky beast, and never seems to be perfectly tuned. This is not due to lack of trying on my part, I can assure you. There IS a reason why it’s such a pain though: Back in 1975 Honda introduced something called CVCC (Compound Vortex Controlled Combustion) in the newly released Civic as a way to meet stringent new emissions and fuel economy standards laws that were to be met by all manufacturers by 1975.
Most other manufacturers (Namely domestics) tried to solve the problem by running their cars on a leaner fuel-air mixture and using air injection pumps, catalytic converters and other performance inhibiting devices. By the time the U.S. manufacturers had reached the 80’s the Engine displacement VS. Horsepower output figures were abysmal: For example the 4.4 liter V8 found in the 1980 Chevrolet Camaro put out a whopping 120 Horsepower. Honda tried a different approach and realized the easiest way to meet these standards was by simply leaning out the mixture, however if you run too lean eventually you reach a point where you can’t start the combustion process.
That’s where CVCC comes in, it solves that problem through the use of what is essentially miniature extra combustion chamber located in the head itself. By feeding a rich fuel-air mixture into the tiny thimble sized pre-combustion chamber you can then ignite the much leaner mix in the primary chamber. This allows for greater gas mileage, less wasted fuel and much lower emissions. Now scientifically and environmentally speaking this is fairly brilliant, in fact at the time Soichiro Honda openly offered the technology to several American manufacturers who had mixed results integrating the technology into American engines and eventually gave up:
Fast Forward to present day California:
In California, in order to keep your car registered and legal to drive, every 2 years you need to have your car tested for smog output, a test which measures it’s HC (Hydrocarbons) CO (Carbon Monoxide) and NOX (Oxides of Nitrogen) while driving at 15 and 25 mph.
There are 2 parts to the test: The actual “sniffer” test and a visual inspection to make sure you only have factory installed or officially approved equipment on the car. As much as I can appreciate being environmentally conscious there’s one thing that really annoys me when it comes to these laws:
The one that effects me is a law by C.A.R.B. (California Air Resources Board) that states that any modifications done to a car that can effect it’s fuel delivery or emissions must have what is called an Executive Order Number, which shows that the product has been tested and approved by the state. If a company doesn’t want to pay for the relevant testing it’s product will not be legal for use in California, whether it actually meets those smog testing standards or not. So, in effect if I use a Weber, AND pass the sniffer (Ergo test CLEAN) I will still fail the test because the Weber doesn’t come with a CARB E.O. #. (At least not for Hondas). This to me is unacceptable, and it leaves me to battle with this:
Now unfortunately not only did Honda make their carb with 3 Barrels, but they made it very difficult to adjust, in fact if you don’t know exactly what you’re doing, you’re better off leaving it alone. Most carbs are relatively simple to adjust or tune…and yet in comparison adjusting the 3 Barrel Keihin can seem like trying to perform brain surgery with chopsticks.
With this in mind I’ve been stupid/stubborn enough to attempt the impossible and I have not only rebuilt my carburetor but also managed to tune it to pass smog testing, something which I dare say I’m quite proud of. I’ve had an ongoing personal battle with these carbs for many years and after so much time, research, and effort I’m going to pass my knowledge on to anyone who wants it. So, with this in mind my next piece will be about the various components of this nightmare of a carb, and what you need to do in order to dial it in for testing. After that I will do an installation video showing you how to remove the factory carb and put a Weber on it which is not only a LOT easier to tune but will allow you to remove those ugly black boxes, that tangled mess of vacuum tubing and clear up some real estate under the hood. Since I would never use an unapproved carburetor on my car (Insert knowing wink here), I’ll do it all in the name of science!
Ethan – Editor.