Z900A4 running rough

[sprint]

Have just re-build the engine, top end only rings, guides and valves and put the bike back together again after a restoration.

The carbs were stripped and all the removable jets, valves etc ultrasonically cleaned, Alcohol was syringed through all the body orifices and blown through with a foot pump.

Have used some vacuum gauges which are between 7 to 8 in Hg.

Ignition timing has been set up with a strobe and is spot on, though one set of points faces were pitted, which were cleaned, but awaiting replacement points and condensers.

New plugs and suppressor caps fitted

However, it rides like the proverbial 'S.O.S'. Starts OK but at tick over No 1 pot continually pops and misfires but seems to clear once warmed up and the engine snatches and chatters at times and does not pick up cleanly.

Pulling away is difficult as it seems that not all pots are pulling together and you have to rev it to get going. At the lower revs, below 2K it snatches and chatters and does not pull evenly. Opening the throttle does not produce a responsive and smooth pickup.

Above 2K it is much smoother but it feels that it is not running in unison and is holding back and again the throttle is not responsive.

Removed the plugs and No 1 and 4 are running OK but No's 2 and 3 were black and sooty.

Where do I start? Is it a carb or ignition problem and what do I need to look for and investigate?

[steve bowdler]

I would re check fuel height in float bowls first

[sprint]

I would re check fuel height in float bowls first

Thanks for the reply.

I did check them individually and they were all around the 3 to 4 mm.

However, on putting them back on the bike they were all leaking. So re-checked them but decided to remove the bowls and bend the tabs up a bit and re-measured. Still all around the 4 mm level. Unfortunately still leaking and would appear to be the the feed pipe 'T' nipples, so have ordered pair of new ones.

So I can measure them again but they should all be around the 4 mm level?

[Pigford]

Swap coils/plugs/leads.... as 1+4, 2+3 are linked.

Check voltage feed to coils when running .... + 12v is vital.

[walshyco]

Agreed with Piggy, I reckon it is probably the condenser hence the pitted points. Good Luck.

[sprint]

Have measured the levels again and if anything they are now all a bit low? Measured at the front edge, near barrel, they are around the 5 mm mark and in fact the 1 and 4 plugs are more or less white so running too weak?

Is that something the air screws will/can correct or do I now need to raise the levels now?

Will try swapping over the coils and see if that transfers the problem, that being the case it must be down to the ignition side, possibly the condenser which may turn up tomorrow and a bit easier to change and try.

In fact it might be worth just swapping the existing condenser leads over first and see if the problem moves with it?

[Pigford]

Have measured the levels again and if anything they are now all a bit low? Measured at the front edge, near barrel, they are around the 5 mm mark and in fact the 1 and 4 plugs are more or less white so running too weak?

NOT NECESSARILY AS MODERN FUEL DOES NOT SHOW THE COLOURS (TAN) SO MUCH - FUEL LEVEL, TOO LOW AND MAKES IT A BIT LEANER

Is that something the air screws will/can correct or do I now need to raise the levels now?

AIR SCREWS WILL EFFECT MIXTURE TO SOME EXTENT - MAINLY 0 - 1/4 THROTTLE, WHILST NEEDLES 1/4 - 3/4 THROTTLE (APPROX)

Will try swapping over the coils and see if that transfers the problem, that being the case it must be down to the ignition side, possibly the condenser which may turn up tomorrow and a bit easier to change and try.

[sprint]

Having replaced the 'T' nipples and wet and dried the top faces of the bowls the carbs seem to be leak tight, but time will tell.

Have re-fitted the carbs and checked the levels again which all come out around the 4 mm level also fitted new points and condensers.

Ignition timing checked with strobe and OK and the No 2 and 3 plugs are now not so sooty but it still rides like a S.O.S with the same problems as originally reported, in fact is is actually worse as before once you got above 2 to 2.5K it actually smoothed out and was a bit more responsive now it is crap from tick over all the time. Starts OK but has rough tick over even though the carbs have been balanced giving around 8 in Hg. Putting hand over the ends of No 3 and 4 exhausts you got warm exhaust but No's 1 and 2 produced practically no heat?

Struggling with this as I do not know what to concentrate on is it an ignition problem or carb issue?

[steve bowdler]

Are you sure your spark plugs are good , some shit ones out there

[sprint]

Are you sure your spark plugs are good , some shit ones out there

Brand new NGK's and suppressor caps. Could try the the original plus and caps, nothing to loose?

[keith mayall]

ive had lots of bad ngk plugs so I got denso..much better and not off ebay www.sparkplugs.co.uk get the carbs right as well.also is the fuel cap breather clear.

[Farmer]

What about between the carbs and the head are you sucking air there ? 😊

[ZedHead]

ive had lots of bad ngk plugs so I got denso..much better and not off ebay www.sparkplugs.co.uk get the carbs right as well.also is the fuel cap breather clear.

Lots of fake NGK plugs about. Genuine ones are fine.

http://www.saisei-europe.com/Shop/Produ ... park-plugs

[Mowjoe]

Are you totally happy with the valve clearances and timing. Sounds like it could be a tooth or two out? Just a thought!

[davejames]

Change plugs for Denso's