Topic: 1978 CB550K Jumps to Full Throttle after Starting

[msh1285]

I just cleaned and put the carbs back together on my '78 CB550K and started her up for the first time. No problems there but when starting the bike immediately jumps to 6,500rpm and stays there. I didn't keep it running longer than a few seconds for fear that something might happen to it. Obviously something to do with the throttle but I have no idea what. I'm pretty new to the motorcycle mechanic stuff and if anyone has an idea I'd really appreciate it.

Thanks!

[calj737]

Have you reset the idle screw? You say "cleaned" the carbs, can you provide some more specifics?

Also, double check that the push/pull cables are properly installed on the linkage. You may have the wrong cable "pulling" the carbs open, hence it's revving the engine. All easy things to check, and all easy things to overlook.

[msh1285]

The idle screw is completely backed out at the moment, just barely touching the plate. I'm not sure what you mean by reset it.

I used this guide below to clean/rebuild the carbs. It seemed all-encompassing, but perhaps I missed something along the way.

https://s3.amazonaws.com/sohc4-tech/CB550/PD46A_rebuild.pdf

I'll double check the cables when I get home from work tonight and see if that was the cause. I had just assumed the longer cable went around the bottom of the actuator plate since it needed more cable to fit there. Maybe that wasn't right.

Thanks!

[flybox1]

bench sync done? while your carbs were off the bike, did you verify your slides were completely DOWN when the idle set screw was backed out?
boots on tight enough to not cause an air leak?
slides hanging up because of yur throttle cables or do your slides snap down  when throttle released?

[eigenvector]

Is your choke stuck on?

[TwoTired]

https://s3.amazonaws.com/sohc4-tech/CB550/PD46A_rebuild.pdf

Pity except for using pine sol used to etch away metal from the metal carb parts and the totally unnecessary complete disassembly, it seems a decent write up.

Check your choke linkage is retracing all the way clear of the fast idle stop screw, and or adjust your fast idle screw.

Ensure you haven't swapped slides among the carb bodies which would allow the slide cutaways to face the engine rather than the air filter as they should.

[PeWe]

Full throttle direct when cold is how I rode my bike back in the days. The piston rings however, did not like it at all. They all went into many pieces