A "Carb Tune" For Honda
A GARB TUNE FOR HONDA
A New Device, Carried Permanently On The CB750, Takes The Headache, And Expense, Out Of Balancing Four Carburetors.
WITH FOUR CYLINDERS, a cush-drive in the rear sprocket assembly and meticulously worked out carburetion, the Honda CB750 is one of the smoothest motorcycles in the world. If the four carburetors become maladjusted, however, the feeling of riding a smooth running electric motor gives way to a feeling of frustration.
Trying to adjust the carburetors by ear rarely gives satisfactory results, and with a minimum flat rate labor charge of $7 to have the carburetors adjusted at the local Honda shop, many owners (more than 36,000 of them) content themselves with riding their CB750s in less than perfect tune.
Now the enterprising CB750 owner with even minimal mechanical experience can adjust his carburetors, using a permanently installed unit which costs about as much as four trips to the shop.
Multiple carburetors must be kept very accurately balanced if the machine is to run smoothly. This is most often done by measuring the vacuum in each carburetor, then equalizing the differences in the readings obtained.
The vacuum measuring apparatus used in Honda service shops consists of four separate gauges, with a vacuum line coming from each of the four carburetors. Although the mechanic can read all four carburetors’ vacuums at once, the assembly costs over $60, dealer net. Therefore it is not practical for the single owner. A much less expensive unit is available from Bowman Products, and it works just as well.
Using the instructions that come with the “Carb-Tune,” and the owner’s manual, synchronizing the four carburetors becomes quite easy. Owners report that after performing the adjustment sequence a few times, they are able to tune their machines perfectly in about 1 5 min.!
To simplify construction of the Carb-Tune, and to eliminate any possibility of inaccuracy between multiple gauges, Bowman Products has chosen to use only one large vacuum gauge mounted on a log manifold.
Each cylinder’s vacuum take-off from the carburetor terminates in a thumbscrew on the manifold. These screws are tapered and fitted with a rubber o-ring. The lower taper fits into a similar taper in the manifold, which completely shuts off the air when fully screwed in.
By following the instructions, which include making sure the valves and timing are set to Honda specifications, we were able to obtain excellent results in about 25 min. With practice, the time could be shortened considerably. As long as the steps are followed, it’s pretty difficult not to get good results.
Installation is very simple, but a couple of precautions should be followed. First, wire the rubber hoses to the carburetor vacuum screws (supplied with the kit), and to the manifold. This will prevent any possibility of moving the hose off the screws and obtaining an incorrect reading. Another safeguard is wrapping electrical tape around the four hoses where they might come into contact with the rear chainguard.
Being a permanent part of the machine, the Carb-Tune need not be worried about. The rubber hoses should be replaced when they show signs of cracking, of course.
The price, including shipping, is $29.95.
