CB400 only firing on one cylinder

[frogdon]

Hi guys,

I'm new to this forum (and CB400's - my firts big 'un). I'm trying to gain a little mechanical knowledge, but I think I may be falling at the first hurdle

Received my 1995 CB400 F2 on Friday, started OK. Cleaned her up and started her a few times over the weekend, all still looking good.

MOT booked for today, so last night I nipped up the indicator switches (previous owner had added Renthal bars) by adding inner tube to give it something to grip to (short term fix - amalgamation tape is being sought) and cleaned her up a bit more. Again, started OK.

Came to start her this morning - all excited as it's my first ride on her - and nothing. Turns over, but refuses to start. Only one manifold pipe is warm (right-most as you sit on the bike). Checked all the connections I can find, but nothing would make her start despite trying for 10 minutes with different levels of choke etc.

I've checked the choke is working (incase I'd misplaced the cable), and it definately moves on top of the carb.

Any suggestions? I'm sourcing a battery charger in case it's that, but would that not try a few times and then fail? And if so, why only on one cylinder?

As I said, I'm new to this, so any suggestions would be much appreciated!

[frogdon]

One final thing... I put new unleaded in it before starting it yesterday.

[amorti]

After trying for 10 minutes to start it, it will be the battery by now if it wasn't before.

Can you get a jump start from a car? That'll usually beast most stubborn bikes which can start, into starting. It is very common for a battery to get down to about 75% (maybe you've been starting it on/off in the garage a lot?) and then it has enough to spark the engine, or enough to run the starter motor, but not both at the same time.

[frogdon]

Cheers Amorti; I'll give that a go.

[Superjack44]

How much fuel did you put in?
Make sure the petrol tap is in the right position Pointing straight up for main and straight down for reserve.
Make sure the vent pipe is clear, thats the small pipe on the right side underneath the tank, blow through both ways back into the tank and down through the rubber pipe to make sure it's clear it must breathe easily.
Check the petrol tap water trap remove the small bowl underneath the tap 10mm nut it should be clean,if it's full of rubbish clean out job required.

[frogdon]

Hi Superjack.

I put in 5 litres of unleaded, and tried the fuel tap on main and reserve - same effect either way.

I'll try the rest of your suggestions tonight... many thanks.

[Superjack44]

Be aware that the tap is operated by vacumm from number one cylinder make sure there is vacumm otherwise fuel will not flow into the carbs.
I check by disconnecting the fuel pipe and watch to see if the tap opens by placing a small bore rubber pipe/tube on the tap and sucking to create the vacumm needed to open the tap.

[frogdon]

OK.. Battery was fine, but is now fully charged anyway (still wouldn't start though).

Tanks now off. Wiring is fragile (tank earth snapped when I moved the tank and made it a little tight, so that'll need fixing as well ).

Is the vent pipe the little metal pipe coming out of the bottom of the tank? If so, I can blow into both of them, but can't find any rubber attachments to check... They seem to be just going into thin air.

Water trap was spotless

Tank leaks out of the top when upside down,.. Is this normal?

Other than that, all looked secure and relatively tidy.

I need a rubber pipe to check the vacuum... I'll get that tomorrow I think (when I'm getting my electrical connectors)

[Superjack44]

There should be two rubber pipes one( bigger of the two) to drain the tank filler recess and the smaller one to allow the tank to breathe they drop down through the frame and are push mounted in a small metal clip fastened to the bottom of the engine.
Try opening the drain screws on the bottom of the carbs to see if there is any fuel in the carbs if not
Next job take the fuel pipe off the petrol tap and place a small pipe onto the vacumm pipe on the petrol tap and suck on it to open it you should feel it opening and petrol should be seen to come out there should be a good flow once you stop sucking the flow should cease immediately.

[frogdon]

Cheers superjack. I don't get fuel through the tap when I suck on the pipe. Ive tried shortening the pipe, and sucking on the tap directly, with no joy.

Disassembled and cleaned the tap. What I found was that I can blow/suck through the tap until I add t centre section (the bit with the black disc that change based on the pressure I guess). Even if I cover the holes of the main section I can suck through, until I add this middle section.

I'm going to dig through the manual, and see if i can find a diagram of how this should fit together.

Cheers again.