QuestionHi Bill!
I've got a '72 CB450, and last night I took my bike on the freeway. No matter how far I pulled the throttle, it would not go past 3500rpm. It SUCKED going only 45mph! If I let off full throttle it would stay at 3500 until the normal place in the throttle range where it usually drops below 3500. It would not idle once warmed up.
With the clutch pulled-in it could go over 3500. It could be carbs. I just hope not. The guy I recently bought it from hadn't ridden the bike in 20 years, and the carbs were cleaned & rebuilt before I got it. It may have had old gas, though. It ran great up until 2 weeks ago.
I just put in new plugs. I'm thinking its the points or timing. When it was cold it would idle, so I should be able to set the timing before she heats up. I'm going to check the fuel filter too. What do ya think?
I'm just looking for some direction to keep from having to do a bunch of extra work. MANY THANKS!
AnswerAlan, set the timing carefully, but make sure that the mechanical spark advancer, located behind the point plate is functioning properly. Otherwise your timing will never be correct. Timing isn't affected hot or cold unless the advancer is sticking on one condition or the other or a condenser is breaking down when hot.
Check the fuel flow through the petcock (fuel valve) to be sure that both sides are flowing properly and that there is no debris blocking the screen or the sediment bowl.
Drop the float bowls to see what it looks like inside. Check the bottom of the bowls for signs of water or debris.
Sometimes the float valves get blocked from the back side by debris that comes down the fuel lines from a contaminated fuel tank.
If the carbs were rebuilt and not contaminated by old fuel, then I suspect that the small vent holes in the gas cap are plugged up from sitting causing a vacuum lock on the fuel as you ride. Clean the small holes with a toothpick or small drill bit, flush the holes and cap with some carb cleaner or blow them out with compressed air.
Bill Silver
