Z1000j ....pilot jets...pop.pop.pop.

[timyoungman]

I am setting up a Z1000j engine with a neta 4-1 exhaust. The engine ticks over fine and is good/smooth at high revs. but between 1500-2000 there is a fair bit of popping and banging both in the zorst and back thru the carbs. I am presuming the mix is too rich ??? and have tried to open up the air mix screws but with little success. The maunal says 1 and 1/4 turns out but I am nearer to 2 turns out now on all four carbs...I have standard pilots jets fitted...so, should I use bigger pilot jets and if so what size ??

I have already thoroughly cleaned out all jets and set floats etc....

Any advice appreciated...

Thanks.

[Al]

Tim, best advice i can offer is to get a 14mm colourtune and run it in all four carbs.
I set mine just a little richer (yellow) than the recommended bunsen blue colour at 1000 RPM because they like a rich mixture low down and need a lot of choke to get them going.
That is to say; adjust them 'till you see the whiteish colour dissappear and a yellow corona appear round the outside of the blue 'core'.

Then lift the throttle to 1500 and see if it turns back to blue or even white at the periphery. (not what you want).
This may be at 1 1/4, 2 or even 2 1/2 turns or whatever it takes.

If its in excess of two turns out then there may well still be a restriction in the pilot capillaries assuming the dynamic (running) float heights are correct. If the float heights are set too low you may well need to open the pilot fuel screws too much to compensate for this.

If set absolutely correctly then you will get some popping and banging back through the carbs and this, i believe is due to weakness, not overly rich mixture but i stand to be corrected.
Popping and banging dissappears when fully off choke and warmed sufficiently. On mine about a couple of minutes maximum.

Lift the throttle to 2 or 3000 and see what happens in the transition from pilot to jet needle. Colour wise i mean.
With a little time and observation it should be possible to get them to run perfectly with no noticeable faults.


Some tests:...
Dont forget the jets screwed into the bottom of the float bowls.
Take out the pilot fuel screws and examine the ends carefully they are thin as pins.
Fill the pilot fuel screw holes with WD40 and see if any of them drain through at a slower rate than others.
Spray WD40 with its straw down through the jet holes in the bottom of the foalt bowls and see that it emerges into the bowl through the holes at the bottom.
Remove the pilot jets and hold them up to the light. If blocked with water (very usual for me) blow through and and replace after firing WD40 through the pilot jet seat holes (vertically upward).
Test the flow rate of the individual pilot jets. Mikuni tolerance is +- 10% per jet, from new so if partially blocked, replaced with pattern ones or burred where the screwdriver goes into the slot, rectify as appropriate.
I used a graduated bottle of water suspended above the sink with a bit of windscreen washer tube fitter to it and the jet screwed into the end of the tube. Very surprised by the result.
If you do need to increase the size of the pilot jets, dont buy new, just ream them out 'till they are all the same size with gas jet nozzle cleaners.
I increased the flow rate by 10% using the bottle and timing over one and a half minutes.
Make sure the vent in the fuel tank cap is breathing correctly. Mine has swollen probably due to ethanol in fuel attacking the rubber 'O' rings and prevented the transfer of air and vapour.

And so on and so on.

AL