Z1OwnersClub GB

Basically ran out of idea's and patience!!
Spent the last 6-7 weeks going round in circles.
Z1 engined bike won't rev above 3500 rpm under load.
If I go in the garage and whistle, the tank, carbs and points cover jump off by themselves, they've been off so many times.
Fuel flow checked.
Carbs dismantled twice, cleaned and float heights checked.
New plugs.
New leads.
New wiring loom.
Ignition system removed, returned to manufacturer, checked and refitted.
Ignition timing checked and ok.
Engine has been rebuilt and valve clearances adjusted prior to my purchase.
Next stage is to start taking the motor apart to check valve timing and clearances.
Spent ages looking back through the help pages but nothing similar appears to be there.
But I may be missing something obvious, so if anyone can have a look at it, that would be great or recommend anyone that I can load it up and take it to.
Cheers.

very likely valve timing out. have you done a compression test ?

I haven't carried out a compression check yet, as I don't have a gauge but I should be able to borrow one.
Engine has recently been rebuilt and I'm sure everythings in order.
I'll report back once I've carried out a check.

Check advancer behind points plate make sure the bob weights move free

Thanks for the replies.
Ignition system is the Boyer Branden Micro Power unit, which does away with the advance mechanism. I've returned the system to them to check it's functioning ok and it's come back with a clean bill of health.
Still scratching my head!

What exhaust are you using ? What carbs ? Jet sizes ?

Thanks for the responses.
The exhaust is a 4 into 2 under seat exhaust.
The carbs are standard 26mm with 120 main jets and K&N type filters.
I've stripped the carbs twice, fully cleaned and checked everything. then reassembled them and set the float heights.
The symptoms have remained the same regardless of the work I've done.
I haven't tried another set of carbs yet, so that may be worth trying. I have another set on a Z1000 project bike I have but they'll need a good clean and check before fitting.
Sometimes when first started the bike appears to be crisper and runs evenly but when you go to ride it, it won't run cleanly under load and won't rev above about 3500 rpm.
At other times the bike will run unevenly and cut out and when trying to restart it, the bike sounds like it's struggling to turn over freely, like it's locking up. As previously suggested, I'll check the valve timing, when I have time.
If I don't see the bike for a few days, I'll get a bit more enthusiasm to try some more ideas!

have you tried anther set of ignition coils? & what voltage do you have at the coils it should be battery voltage when they are disconnected from the coils ?

I've checked the voltage at the coils, which is just over 12v and also checked the power, carrying out the 'headlamp bulb check' so there is sufficient power as well.
The coils are the Boyer Bransden micro coils and have been sent back and checked by the manufactures and passed ok.

get it on a dyno see what the fuel air mix is like,with an underseat pipe and k&n "type" filters which in my experience are shit as they dont flow enough air you need to get a good idea of what the fueling is like

Have you tried rejecting it ..drop mains to std that should give you something to go with wether it's better or worse ..

Thanks again for the advice.
Not sure what the original jetting would be, could it be 110's?. Currently have 120's in there. I think I have a set of 117.5 jets but do you think it's worth trying a much smaller size?

standard main jet for the a1 is 107.5