Motorcycle Repair: throttle handle, throttle linkage, vacuum leak

Question
1894 Honda 700 nite hawk for my son cleaned carbs but the throttle does not return starts fine but if you load it open throttle if sputters and conks out have to turn throttle forward and the bike does not always shut down some times it revs up

Answer
Tom, your 1984 CB700SC may have a combination of mis-adjusted choke and throttle cables to start with. Verify that you do have some free-play slack at the throttle handle when the carbs are all shut down to the idle speed screw. There should be a little bit of a rest between turning the throttle open and hard closed again. Look at the cables and throttle linkage to see that they are adjusted correctly. The choke has a fast idle function, so make sure that it is also set up properly so that turning the choke OFF creates some slack in the cable end to the choke linkage. These bikes are cold-blooded, so you do need to start them with full choke and keep a lot of it going until the engine warms up.

Getting these bikes fired back up after draining the carbs can cause the battery to wear down, if you don't apply some vacuum to the diaphragm fitting on the petcock to help refill the carb float bowls. You can use a section of hose and just suck on it or use a vacuum pump to apply steady pressure to the fitting. There are two fittings on the back side of the diaphragm housing, which look alike. One applies vacuum to the diaphragm and the other one is just a vent to atmosphere. If you hook them up backwards, you don't get fuel flow. If the diaphragm is damaged, you get a vacuum leak and no fuel flow at the same time.

There is a fuel filter inside the fuel tank, so you might want to check it for any blockages due to old gasoline, water residue or other contamination.

Make sure you have the right vacuum lines hooked up to the correct fittings, too.

Bill Silver