SOHC.co.uk Forums > CB350/400
IDLE PROBLEMS CB400/4
Nurse Julie:
Well Dave, if you send me over the gauges you 'acquired' I will have a go. But in the meantime, it's such a fantastic evening, I'm off out for a ride and a rough bit of idle isn't going to stop me having fun.
kevski:
Have you checked the vacuum take off screws, as they only have a copper washer they can sometimes let by, i always put a twist of ptfe tape around these.
Nurse Julie:
I have got new aluminum sealing washers in place and I'm sure they are not leaking as only idles high when hot.
K2-K6:
It's an interesting problem, certainly with others saying the same in trying to get a constant idle.
Also the bit about running rich confuses me as anything I've worked with will usually hunt and drop rpm, eventually stalling if running rich at idle. Usually you'd have to give it more air to keep it going.
I always associate increasing idle with extra air assuming everything else is ok.
They use an air bleed on many fuel injected cars to control the idle with just a small amount of air bleed to raise even something like a V8 of 4lts, it's a surprisingly small amount. It's why many latter engines have o-rings on the dipstick, as when you pull it out it changes the idle as crankcase is vented into the intake systems.
S'pose it could be drawing some small amount of air down the inlet valve guides when hot if they've got a bit of wear of them.
Clem2112:
Air getting down the inlet valve guides sounds possible especially when hot.
Extra hot and slightly oily? air is also pulled in from the crankcase via the air box.
This must vary according to what volume is getting past the rings.
Might be worth checking the drain tube and the manifold vent tube underneath, the handbook says that one of these needs a squeeze periodically !
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