SOHC.co.uk Forums > CB350/400

cb400-four speed.

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Nurse Julie:
It's definitely not running right, or it has a problem, as these are little pocket rockets when running on top form and ridden hard as that's what they were designed for. You do need to use the gears a lot, that's the nature of the bike, they need high revs, they absolutely hate being lugged in the wrong gear.

McCabe-Thiele (Ted):
My 400 will easily reach 70 mph, I expect it would readily reach  90 mph plus if it were legal in the UK.

As Julie  says you need to rev them through the gears, pretty sure mine would do 60 mph in fourth gear with two to spare.

scifi:
Thanks for the replies..
I'm putting two and two together here...
I am unable to get the seat to open, as the lock is stuck.  Also the plugs are a bit sooty.   
So maybe my air cleaners need cleaning, as it is most likely running too rich.

Thanks for all the replies so far..

McCabe-Thiele (Ted):
Figures from 1974 road test on CB400F.
Top speed 98-104 mph in favourable conditions.
6th 98-104 mph
5th 90 -95 mph
4th 82 mph
3rd 68 mph
2nd 52 mph
1st 33 mph

mph/1000 rpm in top 11.
speedo error 4 mph fast at true 70 mph.
Reprinted in Classic Motorcycle mechanics Feb 2010.
             

K2-K6:

--- Quote from: scifi on May 03, 2026, 02:17:43 PM ---Thanks for the replies..
I'm putting two and two together here...
I am unable to get the seat to open, as the lock is stuck.  Also the plugs are a bit sooty.   
So maybe my air cleaners need cleaning, as it is most likely running too rich.

Thanks for all the replies so far..

--- End quote ---

When contemporary, a few friends completed the "I left something under the seat" routine, that to restrict the air intake. Notably a pair of waterproof overtrouser that his bike shop removed for him when he put it in for service because of the poor running  :)

He was suitably embarrassed about that one  ;D

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