Topic: CB400 F experts assistance required

[horror]

Hi there
I have this old clump of metal I got off ebay for a cheap bike. I have tarted it up a bit since then.
(somebody tried to steal it too)



I wanted to see if any other 400 four owners have experienced the problem I'm having.

This bike has been running good for a couple of months, doing 40 mile daily trips to work several days at a time.

The problem is that now, if I set off in the morning the bike is fine as I ride through traffic for the first 10 miles or so, Then it seems once I get on the motorway and open her up, It does 80mph - 90 for a couple of miles then the cylinders start to shut down.
I end up limping along on one cylinder and the others are just dead.

This will last for the entire motorway part, Once I come back into a stop/start town riding situation, the othe rcylinders seem to start to
come back to life a bit. but in a spluttery sort of way.

I thought it may be the carbs but I had them off and cleaned them out but it's still the same.

Could it be overheating due to the unleaded fuel? as far as I can tell everything' standard apart from the exhaust. the main jets are stock i think.

Thanks for any suggestions of what this problem may be, I'm confused a bit

[scunny]

sounds like fuel starvation. pull the hose off the petcock and see if you have a nice constant flow. can also be a cap vent block, when bike starts to stumble pop the petrol cap open and see if the motor fires evenly.

[horror]

Thanks, cheers. the bike had no petrol cap when I bought it so I used a temporary one from the petrol station. It has no sealing capabilities
at all ha ha.

I did notice that the fuel tap (petcock in yank) has no filter inside the tank, Instead there is a rather tired looking inline
filter on te pipe. Maybe that's the source of this starvation that may be happening. blocked inline flter.

Aso the tank was contaminated with lots of red paint flakes from the previous owners paint job, that #$%* could have blocked it cheers for the suggestion

It seems wierd how the thing will go down to  one cylinder, but seemingly run all day on that one remaining cylinder.

[Bodi]

The fuel enters between 2 and 3, so 1 and 4 starve first then either 2 or 3 - whichever one is a bit lower at the nipple.
A plugged fuel filter will do exactly what's happening to you. The paint flakes are a clue that there's a lot of stuff to filter out. The petcocke "filter" is a fine plastic mesh "sock" over the parts inside the tank, it can plug up too and is often removed when people remove the petcock for servicing. It's a pretty good filter and is still, I think, available from Honda.
Riding like this leans out the engine as it starves for fuel, it burns extra hot when lean and can cause trouble if not resolved.
There are rabid anti-inline filter folks on this board, personally I like them and use them on every bike. No problems in 40+ years, just replace them when clogged. I carry a spare in the toolkit, it's about 1 1/2" long and 1/2" around. Filtering out all the grunge saves a lot of grief with the float valves.

[flybox1]

sounds just like a dirty fuel delivery system.
First.  get your tank cleaned.
got some coffee filters, a lg funnel, and a few pint jars?
slosh your tank around and filter out the gas into the jars.
Repeat until little or no flakes are visible in the filters.
you may need to resort to more drastic/toxic measures to get the rust bits out.
if you can get it really clean, you may or may not want to use an inline filter 
second.  remove and clean all parts of your carbs. 
get under the main jets to the emulsifier tubes. 
ensure all the tiny holes on the sides are open and clean.
set the floats, bench sync them.
if any of your fuel hoses are old, replace them.
you should be good to go...

[horror]

Yea thanks I'm going to do all of this. The other day I stripped the carbs and checked out the emulsifier tubes etc.
that was what I thought it was but then same thing.

I had an incling it could have been the filter but for some reason I never acted on that #$%*.

Ill try it out like

[horror]

Yea fuel starvation was bang on the money. I took out my pet cock and it was completely blocked with
paint flakes. what a twat I should have just used the old noggin instead of jumping on the web.

Advice = do not try to whip out the fuel tap and shove a funnel under quickly to catch the petrol that comes out of the full tank.
especially when the lid is still on the fuel can You intend to capture it all in.
schoolboy error. I actually did this. a tidle wave of petrol gushed down my street. what a knob