Z1OwnersClub GB

No1 not firing.Have compression but no vacuum.
Not used compression gauges but you can feel a good compression with your finger


DOES THIS HELP
this started after changing valve oil seals.
compression 1=110 2=95 3=95 4=95

vacuum 1=0 2=20 3=22 4=21

Sticking intake valve maybe?

Check valve / shim clearance

See my last thread m8, might help. I'm still have a problem with No 1 pot but It's firing at least, the header pipes just not as hot as the other 3. I'm now down to a blocked / dirty carb or a duff silicone HT lead but now leaning towards the carb as the problem.

Have you looked to the vac take off blanking bungs?
Had a couple recently that may as well have not been there for all the good they did.
Holed through in the moulding process!!

AL

Im no expert But hows it possible to have compression & no vacuum.
If the valves gaps are to tight there would be no compression.If they are to big may be a bit tappy.But would still be ok to work even if not at its best.

Is there a vacuum circuit in the carb that could be block

zman wrote:Im no expert But hows it possible to have compression & no vacuum.
If the valves gaps are to tight there would be no compression.If they are to big may be a bit tappy.But would still be ok to work even if not at its best.

Is there a vacuum circuit in the carb that could be block

Good question. 2 thoughts - 1 If you have the spark plug out to finger test compression don't expect to draw a vacuum at through the carb with the pug still out. 2. A leak in the intake rubbers/vac take off plugs as per Zorded.

Finger for compression but what are you using to determine lack of vacuum on number 1?
Yes you will get compression with no vacuum because the cylinder can draw air through the exhaust valve if it needs to in a dynamic system that it being tested statically.
Its the expanded gasses clearing the cylinder which in part account for the lower pressure in the cylinder which draws in a new charge. That and the downward movement of the piston. Again though that is running dynamically which brings me back to my question above.
My comment about vac take off bungs reflects the fact that with a bung missing or damaged that would be enough to stop the vacuum developing in the inlet manifold and kill that cylinder.
On my bike that will stop the engine because that cylinder then reverts to pump mode and with nearly 11.5:1 compression it conks out.
If yours will continue to run on three cylinders it implies low compression and thereby low pumping or correct compression and low vacuum.
Its also true that, cam timing makes a significant contribution to both compression and vacuum.
We need numbers

AL

We need numbers but just not those numbers .
Valve timing appear to be more or less spot on.
Compression across the board could be better though and just seems a bit on the low side.
Its conspicuous that #1 has the highest comp and still zero vacuum so i will stick to my original thought that there is a massive air leak on the inlet side.
Its the only thing that might partly explain both sets of numbers but even then i am still not remotely sure.
I take it that you have used the standard method for comp testing;
Same number of spins per cylinder, fuel removed from carbs, bike upright, oil level correct, all plugs removed, throttle pinned etc etc etc.
Does it have a vacuum fuel tap? If so which cylinder is it connected to?
Are the carbs still in a good state of balance from where you had been running it previously? Valve clearances all spot on?


AL

Have you got fuel in the carb? No 1 is on the side stand side and sits with the fuel evaporating gradually and silt settling at that end of the feeder tube between the carbs, check for a blockage on top of the needle seat, it's happened to me!

The carb can fill while it's stood, so when you check with the drain screw it looks like there's fuel, then won't refill quick enough to run the cylinder properly.

Quick check while it's running is to squirt easy start or WD40 in the inlet to No1 carb, if it picks up there's your problem.