I think not that mixture can cause this symptom "when in neutral you rev the engine it takes a few seconds to comeback to normal"

The dashpot is supposed to keep it from falling to idle right away:

Carburetor Dashpot

no it dosnt but it has a dampner kind of thing i have scrwed it all the way out but it still does it but its fine in drive its just in neutral or park!

Thanks!

Does your 120Y carburettor have a Throttle Opener?
It may not be corrected connected, then it will hold the throttle open too long.

hi thanks everyone

i just realised that when in neutral you rev the engine it takes a few seconds to comeback to normal maybe more than 10 seconds i checked for sticky linkages but even if you force it up with you hand it still takes time to return to idle speed

is this somthing to do with carb mixture?

Have a look at it in the dark, you'll see it flashing if the leads are dicey.

As for a potential leak a piece of hose with one end in your ear is a good way to listen for whistles and pops.

If it is an actual miss rather than just 'sounding' like a miss then would suspect a spark problem. You would suspect a plug lead or a plug before the coil. The coil would cause a miss on every cylinder. See if you can narrow down the miss to one cylinder (remove a plug lead at a time - while it's missing - and see if it misses more or no different when you pull each lead off. If it makes no difference when you pull one lead off then you've found your problem cylinder. Swap the lead to another cylinder and see if the miss is now on the cylinder you swapped it to. If it does, you've found your problem. If it doesn't, swap the plug.

Vacuum on a stock motor should be close to 20 inches. If you have a high overlap camshaft it will be lower.

Check the directions that come with your vacuum gauge. They will give several things that can cause a low reading.

i highly doubt it as i put in new hotbox gasket and bolted it all up recntly but will check!

could it be a vacuum leak causing low readings though i couldnt find any!

faulty coil? (causing the possible misfire?)

Is it a leak from the exhaust donut? (Connection between manold and engine pipe?). A very common issue.

hi i have questions regarding my 120y a12 engine

at idle near the exhaust you can hear like a missfire and fell it in the exhasut but in the car its not noticable is it a missfire or somthing else?

also i hooked up the vacuum gauge and it read low like 14 or 15 and needle moves up and down slightly.

i tried looking for vacuum leaks but cant find any!

would this symptoms be normal or something i should worry about to much?

Thanks!