QuestionI have just installed new pod air filters to replace the air box. The bike is running rough as I anticipated. Now I want to rejet the carbs to get the performance back. What are the steps involved in determining the right jets then installing them.
AnswerJames, the 77-78 750s had some pretty lean EPA jet settings, so changing either the exhaust or the intake parts will usually send it over the edge, as you have seen. The only really good way to check jetting is to find a shop with a dyno and pay them to dial it in. Lacking that... According to my Honda specs book, a 1977K model has 115 main jets from the factory. If it is not taking throttle under load at higher rpms, then it is WAY too lean. Probably around a 125 may be required, but try 120s first to see what happens. Before you go fiddling with the carbs, be ABSOLUTELY sure that the plugs are fresh, spark plug caps are okay (5k ohms) and that the ignition timing and advance are right on the money. We are assuming you have even and high compression on all cylinders.. right?
Look for signs of leaning out by pulling the choke on just a little bit, when it starts to stumble. If it gets better, then you are still too lean. If worse, then you overdid it.
The carbs are a pain to work on, but if you decide to pull the rack, you may have to raise the needles up a notch or if they are not adjustable, go to ACE and find some tiny little metal washers, that the needle will fit through and put one under the clip. If you do pull the slides and needles, you will have to have the carbs resynchronized before you go back to rejetting again.
Get a nice length small Phillips screwdriver and you may be able to remove the float bowls with the carbs in place, for jetting changes. Find the PARTS FISH or BIKE BANDIT sites for illustrations.
Bill Silver
