So I ride a 72 cb450. Its been running great, then after sitting for about a month, it decided to develop a disorder and I can't for the life of me figure out what the problem is.. I'm thinking electrical, but heres what its doing and hopefully someone has some input that will help..

I kickstart it. Bike in neutral, neutral light illuminated, idling at around 900.... then moments later, it starts surging. the rpms dip and the neutral light dims, then it goes back, then back down, then back up. even if i'm giving it steady throttle, it does the same thing. SO if I was riding, in any gear, say my rpms are at 2000, it would dip down to 1500, then jump back to 2000, and back and forth. Consistently. like 3 seconds at normal, then 3 seconds down, then 3 up, and 3 down....

I've gone through the carbs and tested different air/fuel mixtures, and thats not the issue. Floats are perfect. My only conclusion is that its a coil issue. since the neutral light dims when the rpms dip down, it leads me to believe its an electrical issue. The rectifier is new, the battery is newish (and not the greatest) ...I'm just stumped, and now the weather is amazing and I wanna ride!!! If anyone has any ideas as to what it could be, please share. Thanks!!

 

this happens at any rpms? even when your riding at speed?

 

Yep. I could be riding at 20 mpg at 2500rpm, keeping the throttle steady, and it would do it. Up down up down. Like every few seconds it loses power then regains it.

 

Have you checked your grounds for corrosion? The surging sounds like an air leak due to a cracked boot. The lights dimming and brightening could be from the stator trying to charge a weak battery and run the bike at the same time. Just throwing ideas out there. It has been a long time since I was in tech.

Use carb cleaner to check for an air leak. spray it around the boots, if the idle goes up, you found a leak

 

Try charging the battery

The alternators on CBs are pretty weak and you have to idle above 3k to charge the battery. Also try www.sohc4.net