Topic: CB400F bogs at 7,000 rpm

[mjptexas]

I have a new (to me) 1975 CB400f, 34,000 miles.  Previous owner rebuilt the carbs earlier this year.  The bike starts easily and idles.   It pulls well to about 7,000 rpm then bogs down.  Won't rev any higher.

Any suggestions as to what to look for would be welcomed.

Mike

[robvangulik]

Find a quiet road, get it to that 7000rpm, hold it there for a few minutes, pull the clutch, stop the engine and pull up on a safe place, in that order.
Remove a (or several) spark plugs and look what color the 'nose' is, if light or white you need a bigger mainjet, if dark or black a smaller one.
If light brown or 'tan' you need to search for other causes for the problem!

[jgger]

If the carbs were just done as you say, do a clear tube test for the float level. Could be a low float level. Also check the air box for restrictions,  if you placed anything under the seat it could be choking off the air.

One more thing to try, on a safe stretch of road get it to bog and hold it there and open the gas cap. Could be a clogged cap vent. That is not likely here but it is possible.