SOHC.co.uk Forums > CB350/400

Small problem with my 400

<< < (2/3) > >>

K2-K6:
Hi Shaun

Yes general mixture check would be to get it properly warmed up and then check the plug colour, it should look like a slightly pale milk chocolate colour going whiter is too lean and likely to get too hot, going blacker would be too rich.

If it revs and runs ok at wider throttle opening then it seems like it's not far out as unless someone has previously changed them then it's probable that the jets are standard.

The size of the main jet controls max fuel demand, the needle progressively shuts this off to give less fuel as the throttle is closed toward lower speed.

In addition there is an idle circuit that is more accurate than the above to control the very slow running, hence the questions to try and isolate a particular area of the problem.

They should all work in a linear fashion from clsoe to full throttle but if one parameter has been shifted too much away from ideal you end up with a stepped feel as you've described.

The idle screws should be visible to you, one on each carb a small flat blade brass screw in a casting recess. they are not hard to adjust yourself.

Yoshi823:
The tips of the idle mixture screws used to have a habit of getting coated with fuel residue...something to be aware of when attempting to get the tickover to idle correctly once the float heights had been properly set.

shaunc:
Don't know what I've done now but I decided to have a go at adjusting the idle screw before I went out for a ride this afternoon.  I had a quick look in my Haynes manual for anything that looked like an idle screw but couldn't find anything.  I had a look at the right hand carburettor and saw a black plastic adjuster and something in a similar position on the inside carburettor but metal. Confident these were the idle screws I started to turn the outside one out by half a turn.  Unfortunately, I didn't get to unscrew it half a turn before it stopped.  I then noticed that this black cap had a little thing on it to stop it being turned too far.  Panicking I tried to turn it back to where I thought it came from.

I don't what it was I adjusted but it seems to have made the bike slightly better at picking up when the throttle's closed.   Do you think it is it the idle screw I've adjusted and how come I can't unscrew it any more?

Thanks
Shaun 

PatM:
Shaun- sounds like the mixture screw for idle- the black cap comes off and you can remove the screw- that

K2-K6:
The black cap you speak of is as far as I can tell is to limit the range over which you can adjust the screw.

The method "I think" is to set them up as PatM says and then you'd put the caps back on to effectively give you a small adjustment range that could be used to tweak them when out on a run without having to go and count turns etc again. I think this would be more relevant in coping with altitude to trim the low response just enough to improve running at extremes, don't think it's so useful in the flatlands of UK but central Europe and USA may be a more normal situation with big elevation shifts throughout a trip.

If you do them as PatM says you should be somewhere in the middle of their range and I would expect to see 1/2 turn in either direction to get it as you need if it still didn't feel quite right.

If you find that they need to be very far away from stock it would indicate that something else is influencing it.

Navigation

[0] Message Index

[#] Next page

[*] Previous page