CB400 only firing on one cylinder

[Superjack44]

Just to make sure you are sucking on the vacumm pipe the large bore pipe is the petrol supply pipe and the small bore pipe is the vacumm pipe this is the one you suck on to see if petrol flows through the large bore pipe.
You should not be able to get petrol through the large pipe without operating (creating a vacumm) the small pipe

[frogdon]

Aye, that's the one, thanks.
Although one exhaust pipe gets warm, which made me think it was turning over, the same pipe gets hot warm if I run it with the fuel tap set to off, so I suspect that's red herring. I've drained the tank got my brother round to watch as I suck on the vaccuum pipe, and he's adamant that petrol vapour comes out when I suck (no juice, but there's not a lot left in the tank at the moment).

I suspect that leads me to check that the kind lead and dizzy are connected, and maybe spray some water dispersant into the connectors...?

[amorti]

Aye, that's the one, thanks.
Although one exhaust pipe gets warm, which made me think it was turning over, the same pipe gets hot warm if I run it with the fuel tap set to off, so I suspect that's red herring. I've drained the tank got my brother round to watch as I suck on the vaccuum pipe, and he's adamant that petrol vapour comes out when I suck (no juice, but there's not a lot left in the tank at the moment).

I suspect that leads me to check that the kind lead and dizzy are connected, and maybe spray some water dispersant into the connectors...?

If you're not getting fuel then fix that or any other diagnosis is guesswork.

Maybe the gauze filter is blocked?

[frogdon]

Is the gauze filter inside the tap assembly?

[amorti]

Is the gauze filter inside the tap assembly?

There is one in there, yes. It'd take a fair amount of crud to block it but you are running out of obvious things to check.

[Superjack44]

Agreed the petrol tap needs to be dismantled and cleaned you need a good flow through the petrol tap

[frogdon]

OK, final update... Connected a small pipe to the fuel tap, and turned it over, and fuel came through good. Finally found my spark plug socket, checked spark plugs, and they were black. Replaced, and it now starts on the button

It's not there yet, but next thing on the list is to give it a good run out to clean out the crap

Thanks all for your help.... Much, much, appreciated.

[amorti]

OK, final update... Connected a small pipe to the fuel tap, and turned it over, and fuel came through good. Finally found my spark plug socket, checked spark plugs, and they were black. Replaced, and it now starts on the button

It's not there yet, but next thing on the list is to give it a good run out to clean out the crap

Thanks all for your help.... Much, much, appreciated.

Question is why are the plugs black. Rich mixture?

http://www.spark-plugs.co.uk/pages/tech ... gnosis.htm

[frogdon]

Thanks, I'll check that.

My initial thought is that we've put redex in the night before, and run it for a while. Although not a lot came out of the exhaust, it may have cleaned out the carbs, but only as far as the pistons.

According to my father in law, if I didn't thn leave it for LNG enough to burn the junk in there, next startup would throw the carbon from the pistons onto the sparks, coating them and making them very broken.

If that's the case, it's going to be interesting to see if it starts again tomorrow...

[derry]

if you turn off the fuel switch and let the petrol burn from the carbs by turning over for a min or two,
the plugs get wet from using the choke .if she starts the turn the fuel tap to straight up for on.this is what works for me as she floods easily