1983 Z400J not firing on no 4 cylinder

 Number 4 cylinder has been playing up for a while and has finally stopped firing..Have had the float bowl off  and there's petrol inside it and main jet and emulsion tube are clear. have had the float and needle valve out and cleaned the valve seat. I haven't tried to adjust the float height as I don't know what it should be and bending the metal tab seems a bit imprecise for my big fingers.  Plug and coil are new and there's a good spark and still nothing.  I found out that spraying carb cleaner into the tube sticking out of the inlet manifold makes it fire but once its burnt off still nothing. Same if I spray it into the airbox end of the carb. This points me to the float level as the petrol isn't being sucked up into the venturi part of the carb or is there something else I can look at?

Ey up lad, the 400J carbs are slightly smaller version of my Z500 TK22, looks like you narrowed it down to no fuel. you set the fuel height via the float height so with the bowls off and carbs upside down start at around 18mm from gasket serface to top od the stepped bit of float. measure the other 3 for reference, if 4 is withing 1 or 2 mm of the 1,2,3 then you may have an air passage blocked not a fuel passage.
float height and fuel level explained

 

my float height at 19mm note where i take the 19mm from
 

this gives me a fuel level in spec when i put my clear tube on the over flow out pipe

 

if not fuel take out the pilot jet , idle mixture screw and spring on no4 and spray carb cleaner down the air passage on back of carb and see if it comes out of the pilot jet hole and then down mixture screw hole  also clear out the main air passage hole at the back.

tell us how you get on. plenty red rubber grease on the inlet rubbers to get them on easier

 

How old are your carb mounts? Air leaks between the carb and head can also cause it not to draw fuel

Great pictures and explanations, this is just what i need. I tried the clear plastic tube from the overflow fitting yesterday and found that No4 was just below the bowl gasket line,then compared it to No1 which was bang on the gasket line, so tried bending the metal tang on the float down a bit. I'm going to start it today (I'm a bit limited by noise as my wife works above the garage) and see if there's any improvement. Lovely clean engine and carbs on your 550

Wookie58 wrote:

How old are your carb mounts? Air leaks between the carb and head can also cause it not to draw fuel

I would say just on appearance they are most likely the originals. I have sprayed carb cleaner on the  engine side rubber mounts and it seems to be OK. The airbox side rubbers are harder than a 15yr old with a flick knife.

 

zedordead wrote:

Wookie58 wrote:

How old are your carb mounts? Air leaks between the carb and head can also cause it not to draw fuel

I would say just on appearance they are most likely the originals. I have sprayed carb cleaner on the  engine side rubber mounts and it seems to be OK. The airbox side rubbers are harder than a 15yr old with a flick knife.

 

Spraying them doesn't always give a reliable indication. From everything I have seen on this forum it's almost "a given" that if the rubbers are that old then they won't be sealing as they should.

How's compression?  Valve clearances in spec?

Wookie58 wrote:

zedordead wrote:

Wookie58 wrote:

How old are your carb mounts? Air leaks between the carb and head can also cause it not to draw fuel

I would say just on appearance they are most likely the originals. I have sprayed carb cleaner on the  engine side rubber mounts and it seems to be OK. The airbox side rubbers are harder than a 15yr old with a flick knife.

 

Spraying them doesn't always give a reliable indication. From everything I have seen on this forum it's almost "a given" that if the rubbers are that old then they won't be sealing as they should.

Good to know, It's something worth looking into but for now its running on N04. I took the carbs off the bike and  took the bottom half apart and sprayed carb cleaner through everything as advised above and i'm as certain as I can be that nothing is blocked.  I did the same to the other three and they look in good nick. I didn't dismantle the slides and needles as they all looked well syncronised and  I raised the needles and gave them a good spraying and they look clean enough. The floats on 1-3 were almost identical in height with 4 being the only one I tampered with to let more fuel in.
    Started it up today and No4 still wasn't firing. I haven't put the airbox side rubbers back on yet so I sprayed some carb cleaner in there and it coughed and ran on it. I put my hand over the back on No4 carb and it started running, so in effect I was chocking the one carb leading me to think its running lean. I had all the mixture screws out yesterday and tried to remember how many turns out they were from full in. I've screwed No4 in a bit and its running. I'm going to let it cool down and start it again to see if it was a fluke and then I'm going to watch some Youpube clips on airscrews and mixture setting
 

Nessism wrote:

How's compression?  Valve clearances in spec?

Haven't tested compression properly other than the tried and tested finger in the plug hole and It's sucking through the back of the carb.  I have no idea when the valves were last checked as there was no service history with the bike. its got nearly 56,000 on the clock but who knows?
 

zedordead wrote:

Nessism wrote:

How's compression?  Valve clearances in spec?

Haven't tested compression properly other than the tried and tested finger in the plug hole and It's sucking through the back of the carb.  I have no idea when the valves were last checked as there was no service history with the bike. its got nearly 56,000 on the clock but who knows?

 

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Regarding the valves, you might want to read through this... www.kzrider.com/forum/forum-index/faq-wi...owner-things-to-know