QuestionI'm about to install a pair of NOS carbs on my 74 cb450 and was unsure if I need to make any adjustments to them before installation, I also plan on upgrading to pod style filters after I get the bike running, any tips on how to setup the carbs once the new filters are installed?
AnswerChris, lucky you to have found new carbs. Are they the exact same ones as those you are replacing? Carbs are stamped with jetting codes on the outside. Look for 14H. 14I, 723A, 727A and 723B stampings on the bodies.
Setting carbs is the LAST thing to do on the bike, during a tune-up or installation of new components.
Check the condition/function of the mechanical spark advancer, behind the point plate. Clean and lubricate it and snug up the return springs with some needlenose pliers if there is some play in the weights. You want the weights to return snugly, to minimize the slop and freeplay in the point cam.
Turn the engine over to find the high spot on the point cam and then check the gap. Should be .012" to .016" maximum.
Turn the plate back and forth so that the left side points open at the LF mark alignment and then the right side to the F mark on the rotor. Once that is set and everything is tightened up, you can start the engine. Use about 1 turn out for the idle screws as a baseline. Be sure that the idle levers, which set the idle speeds are set the same on both sides. Probably about 1/8 to 1/4 turn from where the screws contact the base. Let the engine warm up and set idle screws when the engine is hot. Check part throttle response for any hesistation. Adjust idle screws to highest idle speed, then turn in just a fraction. Check throttle response again. Ride the bike and see if there are big hesitation spots in the idle to 1/8 throttle 1/8 to 1/4 throttle, 1/2 throttle and 1/2 to full throttle.
It is best to go too rich on the main jets when checking full throttle. Main jets vary from 130 to 150 for 450s, depending on calibration. Jetting was designed with standard air filter system and mufflers in mind, so deviations from that may require some different settings.
Get the wide open jetting settings established first, then check the mid range and low speed jetting for flat spots and adjust accordingly. You can shim the clip on the needle if it isn't adjustable.
Honda CV carbs are rather wide ranging in their ability to adapt to system changes without having to do a lot of radical jetting changes, for the most part.
Bill Silver
