Need help diagnosing my 1980 Honda 750c. Jumps to 4K RPM on a cold start

[blingbao]

Hey everyone this is my first time owning a bike and learning how to fix it. I have a 1980 Honda CB 750 C I just recently clean, rebuilt the carbs, and replaced the boots. But when I started it up, the idle jumps to 4000 RPM. The idle would lower when I pull the choke but runs a lil rough. Ive checked the boots to make sure they’re sealed properly, check for any leaks, bench synced, and haven’t fully installed the throttle (throttle mechanism moves freely and snaps back with no issues). My assumption is something can be clogging the carbs or the spark advancer is stuck in an advance position and needs to be serviced. If anyone have an idea or has dealt with this before, any input would really help me out. Again this is my first time dealing with motorcycles so I’m learning and would love to learn more. Thank you!

 

[kirky]

if you mean cold start with the choke on they all do that well mine does

 

[blingbao]

if you mean cold start with the choke on they all do that well mine does

Choke isn’t pulled at all. When it is pulled the idle would be lower but have a bit of sputtering

 

[kirky]

i don't think i can help but the these engines are normally on full advance at about 2500rpm so i think you can rule out that.

 

[blingbao]

i don't think i can help but the these engines are normally on full advance at about 2500rpm so i think you can rule out t

I just figured out the issue. I decided to start over and thoroughly look through everything. Came across the carbs and found the culprit. I put the adjusting screws in the wrong orientation allowing two of the throttle plates on the carbs to be more open than the other two. Removed and reinstalled the adjustment screws in the correct orientation. Looked over everything once again. Ben’s synced. Reinstalled the carbs, boots, and cables. Started her up with the choke pulled all the way and after so many disappointing nights she finally started up beautifully and very healthy. Of course, i got to do a carb sync but there’s no better feeling than finally figuring out the problem and having the answer. Moral of the story, need to double check my work. At the end of the day no matter how hard it is, it’ll get figured out .