Bike Z900 A4 not running correctly (FINALLY SORTED)

[Gray17]

Well This has been a real saga This bike has had a small fortune spent on it. Whilst theres several posts currently running on poor running (read each with interest and comment), mine has been ongoing for a long while to no avail.
Work done so far inc;
1. Full engine strip, vapour blast
2. Carbs stripped ultrasonically cleaned, complete new Keyster carb kits inc all jets replaced. 4 new take off rubbers. Float heights set
3. New viton choke plunger seals ( courtesy of Rob)
4 Cylinder head vapour blasted, skimmed , replaced valve guides, new exhaust valves all seats re cut and lapped (no fuel leakage) no valves sticking all shim clearence on loose side 15thou rather then tight so valves def all closing ok.
5 Barrells re bored, new pistons and rings (IMD)
6. Electronic ignition fitted Dyna S type (no points)
7. New plugs (Denso on recomendation )
8. All new timing guides and rollers fitted.
9. new 4 into 4 exhaust, standard air box and filter.
10 . Engine rebuilt all new gaskets, new oil , filters etc timed up checked 4 times everytime spot on to the marks pretty sure its correct. Everything set to stsndard as per manual.
11. Relay mod done to coils, to ensure good 12v+ and good spark on all plugs.
12. New combined voltage regulator fitted 14v
So engine starts and runs however still very hesitant on throttle, tick over at 1500 wont tick over below that, if you blip throttle it revs then cuts out, runs better on choke, but plugs black ish, havnt taken it for a run as yet, was hoping it would run better but it just doesnt.
Im now at a loss as where to go with it, thought rebore new pistons etc would solve it, but runs the same as before rebore, everything suggested has been done, nothing seems to have had any great effect so far. Clearly somethings not right but what?
Isuggestions other then sell it???

[wheelysteve]

I would think this is still a carb issue. Have you tried another set of proven carbs since the rebuild?

[Gray17]

Thanks for reply, yes its possible, but everything but the bodies has been replaced already, i would gladly try another set of carbs but dont have that facility myself, even advertised sets need fully refurbishing so may end up worst then what ive got now.
However if anyones reading this, lives local( Hull area)/ or ship at my cost and would allow me to try using spare proven set, please PM me.
However understand its a lot to ask!

[stusco]

Do the revs hang when throttle blipped maybe an airleak on the carbs
Spray wd40 around the rubbers if the revs rise theres a leak

[Gray17]

Hi no def not air leak, removed all 4 rubbers previously after Nigels suggestion used 3 bond silver gasket seal around joint to cylinder head and checked with carbs in place seems to be air tight. Rubber is still supple and clamps tightly around carb mouths with clamp tightened. Probably been renewed recently. As stated all 4 take off rubbers renewed amd are a tight fit.
The rear rubber to airbox are a little hard but warmed them up before fitment to soften them up then fitted to rear of carbs, then tightened clamps. Again seem a snug fit, suppose its possible but unlikely, as did the WD test and made no difference to revs.

[kev edwards]

If you have the old exhaust system, put it back on and try it, sometimes the repop exhausts are just not right, how do I know? I think you can guess, filter might also be restricting it.

[Philippe]

Hi Gray17

perhaps a stupid question but did you check the timing advancer? If there's still one mounted since you have an electronic ignition...
If there is one make sure it works correctly: springs can be weak, not enough lubrication on the axles where the weights rotate, a defective thin washer between the plate and the tube where the weights are hooked in,...
If there's no timing advancer mounted, just forget what I wrote.
GrtZ
Philippe

[Gray17]

Thanks for reply, well gluton for punishment, re checked all carb rubbers pretty much 100% sure no carb to head leaks, the rear ones seem sound also but are harder then the front ones but with clamps in place seem to be good. The 4 take offs are all new and seal well.
Believe if theres an air leak its the front that causes the issues rather then rears.
Phillippe yes still using original advance mechanism, stripped it and lubricated it, it seems to work ok, if i put timing light on it doesnt advance at tickover only when revved and mark goes back when revs die so believe its working ok. If springs weak whatceffect would this have, sticking bob weights ( they dont), advancing at tick over ( it doesnt). Id wish it was as a simple fix, but everything suggested has been done, nothings worked so far, or its the way im doing it thats wrong (likely).
Carbs replaced would be good idea if i knew someone who has a good set, but their expensive and may get damaged in transit, not the easiest things to get on and off either, so understand anyones reluctance to loan. Think id be hesitant too.

[Peteypops23]

Hi Graham,
Have you balanced the carbs? It makes one hell of a difference.
Pete

[Gray17]

Hi Pete, thanks for reply, balanced slides on the bench seem very similar openings, however i bought a set of 4 gauges, unfortunately they are useless, so much flickering their effectively unuseable even with the adjusters almost closed, basically a waste of money.
Was hoping to get bike running reasonable then take it somewhere to get it done properly using a dealer with quality gauges rather then trying to guess whats good and whats not. I know carb ballancing makes a big difference to how it pulls and max power getting all 4 cylinders syncronised. But hoped the bike would at least run reasonable as is, alas it doesnt.
However judging by the many posts relating to bad running it seems to be a lot more common, or perhaps like me a lot of the owners struggle to get them running properly, due to lack of said knowledge?
What ive learnt on the journey so far is that 40 year old machinery, needs bottomless pockets and expert knowledge in vast quantities to allow that setting up to get any type of enjoyment from it.
Im sure other owners struggling probably feel the same, when all you want to do is ride it, instead your spending every minute in the garage just trying to get it running, in the hope you may actually get to ride it!

[CAT3]

What exact type/make of vacuum gauge did you buy ?

When you say the vacuum gauges were flickering, are there not adjusters on each gauge to dampen the needles ?
Usually there would be a knurled ring at the bottom of each gauge, where the vacuum pipe connects to, you would just turn this one way or the other until the needle on that gauge is steady.

[Gray17]

Hi,

Sorry no idea who manufacturer is, but advertised as suitable for all 4 clinder motorcycles. Appeared ideal and looked good too.
Came as a kit with 4 gauges on a steel bracket, and 4 lengths of hose, 4 adjustment valves and 8 brass ext nozzles.
When they arrived all were at def atmospheric pressures, so not great, but perspex covers were removed and all 4 set identical, using brass zero screw, Next cut small length of hose and fitted the valves then remainder of hose. Conbected each to take off on carbs, hung from garage roof over tank.
Started bike and adjusted valves, no matter how much i closed or opened the plastic valve, gauge swings was so erratic completely unreadable on all 4. So couldnt even use 1 on each carb at a time.
Gave up in the end. Clearly £39.99 igets you rubbish quality, but how are you supposed to know that,vive seen them at as low as £19.99 and up to over £100, i just assumed a mid price would work, correctly but perhaps not be as accurate, which as long as all read the same didnt matter, but not totally unreadable. Im talking 1/2 the scale deflections at tick over and above.

[kev edwards]

Sadly those gauges are crap at that price, I have Morgan carb tune I bought in the early nineties, from what I've read on this whole thread your problem is your dyna and set up. You would also be better off investing in a morgan carb tune, old adage buy cheap buy twice.

[Gray17]

Hi Kev,
Yes ive discovered that myself, but as stated thought they would be useable, if not that accurate.
Moving on you say the problem sounds like the dyna s setup, in what way? As this was recomended in preference to the existing points system. Theres only 3 wires a 12v + which in my case goes to the coil feed wire from the relay mod along with coil feeds.
The other 2 are coil - , the system works in that you have no moving parts and a decent spark at plugs. Its also statically timed and both are 180deg apart. I do have a zenon timing light and the marks look good and move when revved showing advance working, what else is there?

[zed9]

I always time mine on full advance as this is where engine spends most of the time. To me its more accurate and stable strobing at full advance rarther than tick over.