Sorry guys.
I did'nt explain very clearly.
I never EVER free rev my cars.
I know it is bad for them.
I did the tests in first gear and second gear to see what happens in the rev range.
Never in neutral. The car is is perfect tune.
No miss. and the wheels are in balance. It is something with the engine.

What I forgot to mention.
My clutch was replaced a couple of months ago. They needed to give the flywheel a skim. Can this have caused the flywheel to be out of balance?
I was present with the skim process.
It was done evenly accross the whole flywheel and no step was cut into the flywheel.

sounds like a miss to me too.

some engines do this - technically it should be okay free-revving and holding steady, but generally i have found that (A12s especially) don't like being held at 5000rpm with no load.

let the clutch out though, and the miss disappears.

it could be dizzy float, it could be backlash in the dizzy gears, it could be your points - geezus there's a million things it could be. it could even be as simple as your coil is breaking down or a lead shorting on the rocker cover.

engines aren't designed to be free-revved so chances are they won't like it. rev it to 5000 in first and hold it there and see if it smooths out. if not, then check for problems.

are you sure its tuned ok, Sounds like a miss to me

Hi All

I just want to get people's opinion about something.
As you all know I have the A12GX engine.
This past weekend I decided to drive my car slowly in the revs to see what happens where.
all the way to 3500rpm it is nice and smooth.
At 4000rpm it starts to make alot of engine and exhaust noise and a bit of vibrations.
At 4500 it really starts to make noise and more vibrations and at 5000 it makes alot of vibrations.

I was informed that the engine and exhaust noise is normal as the revs increase.
My question is about the vibrations.
How must the vibrations be if the engine is out of balance.
The vibrations is not like asif the front wheels are out of balance and whole front is shaking it is more like when you have a small hammer drill (Not the big heavy duty ones, but one of those that you buy at a hardware store)and you are busy drilling into a wall with the hammer drill. This is the only way I can explain the vibrations.
Is it not the harmonics of the engine?
I would like to balance the engine but this is the maximum revs I will use as we do not have a race track and I mostly will use it on the roads and rev it a bit hard.
I do not want to spend money that I can use for something else, for example buying a 5 speed gearbox .
Can I drive the car like this or will it later give me problems or cause premature wear.