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Discussion Starter · #1 ·
Not sure which category this would fit in so if it needs to be moved please feel free to. I have a CB450 K7 which I rebuilt the carbs and petcock and replaced the coils, plugs, and points among other things. When trying to accelerate I get to about 40 mph and start to lose power no matter what gear I am in and it eventually dies. I have noticed it happens more often going uphill - not sure if that matters. I made sure there was a full tank of gas and tried switching to reserve to avoid a possible clog in the main section of the petcock. I have also set the timing properly. Any suggestions/help is greatly appreciated.

Thanks!
 

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ride it until is starts to die and pop gas cap, if it picks up, gas cap vent is clogged. Check float level also along with flow rate from tank to carbs.
 

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Try using the choke as well when it does it, might too lean. I don't, but could the floats be adjusted too low and when ride a hill not enough fuel in the bowls to supply the demand?
 

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Discussion Starter · #5 ·
The choke doesn't seem to help it much and when it first started doing this, I opened the carbs again to check for any gunk and clogs and made sure the floats were set according to the manual. It doesn't hurt to recheck them as well.

Is there any diagram or resource for disassembling the tank cap? I'm not exactly sure how it assembled in order to try cleaning it.
 

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My original has a center screw, which holds it together. A replacement cap may be riveted together, and the spring assembly is pressed into the cap, so taking it apart can be a problem. Once apart, getting the parts to stay in again is the next problem.
The usual cause of the blockage is an after-market rubber seal that extends over the hole on the atmosphere side, and difficult to verify without disassembly; if you have one with the screw in the center, not a problem. The little hole on tank side is obvious, and you can clearly see if it is blocked.

BTW, was the tank nearly full? If you siphon about 2 gallons out, it will take longer for the engine to fuel starve, if it is the cap vent.
 

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If it’s riveted, you can usually very gently use a flathead screwdriver under one of the points of the star-shaped flange inside the gas cap. It pops right out, and presses back in easily.
 

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Discussion Starter · #9 ·
Thanks for everyone's help. I removed the cap guts and cleaned them out real good. It seems to have fixed the issue!
 

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