79 CB750F falls flat over 5k RPM

[mrmach5]

79 CB 750F , This bike is new to me . When I got it I did a compression test all four range from 155-160 PSI. Adjusted the valves. Stock exhaust and factory air box. Complete carb (VB42A) rebuild , ultra sonic clean all new o rings, air cut off valves and accel pump. Used all factory brass parts 68 mid jet 102 main jet. Carb sync and dynamic timed. Idles nice and at part throttle it accelerates well . if you pull more throttle if falls over and sputters and won't go over 5k rpm. Brought it home and checked for any vacuum leaks at the boots. Changed out igniters to see if it might be ignition, no change.
Not sure my next move, perhaps a jet change ?

 

[mrmach5]

Checked advancer unit and getting full advance at 4-5krpm . Reset pulse generator air gap. Swapped gas caps. Still no change.
Guess carbs are coming back off,,,,,,,,,, oh joy !!!!

 

[plantguy]

Checked advancer unit and getting full advance at 4-5krpm . Reset pulse generator air gap. Swapped gas caps. Still no change.
Guess carbs are coming back off,,,,,,,,,, oh joy !!!!

Check your charge rate. I had a similar thing happing to my 900. I should put a sticky on my post in this thread.

https://www.cb750.com/threads/cdi-ignition-module.9296/

 

[mrmach5]

Well, file this one under I'm a dumb ass, or if you're gonna be stupid, you gotta be tough .
My problem was totally self induced . During the rebuild process , getting ready to set float height so Googled correct float height for a 79 CB750F and three sources popped up all listing 26mm . After chasing my running issue, off came the carbs again for perhaps a main jet change. Decided to check float height again, this time I see on a forum where a guy posted a photo of the carb specs page from the genuine Honda manual, that listed the float height as 15mm ! at 26mm I'm guessing the main jet wasn't even getting wet.
Feeling pretty stupid that I fell for that rookie mistake, I reset the floats to 15mm and the bike now runs perfect,,,,, imagine that.
Sorry if I wasted anyone's time

 

[PaPa Garry]

Well, file this one under I'm a dumb ass, or if you're gonna be stupid, you gotta be tough .
My problem was totally self induced . During the rebuild process , getting ready to set float height so Googled correct float height for a 79 CB750F and three sources popped up all listing 26mm . After chasing my running issue, off came the carbs again for perhaps a main jet change. Decided to check float height again, this time I see on a forum where a guy posted a photo of the carb specs page from the genuine Honda manual, that listed the float height as 15mm ! at 26mm I'm guessing the main jet wasn't even getting wet.
Feeling pretty stupid that I fell for that rookie mistake, I reset the floats to 15mm and the bike now runs perfect,,,,, imagine that.
Sorry if I wasted anyone's

Good job.

 

[mrtwowheel]

Naw, file that under "good find".