Engine trouble

sounds like the clutch my be the issue. Pull the motor and check the clutch, pressure plate, etc for signs of wear. If the clutch wear surface comes loose from the metal plate it will vibrate  badly

Bet a spark plug popped out!  Either due to not being tight and normal vibration ---- or the threads stripped.  Easy to check for.

Could be a spark plug wire off too - but would no noise then.

No photo attached.

Vibration over 2500 rpm....could it be something to do with the shroud/fan?

Hi Ernie....I had similar symptoms when a sheet of newspaper was sucked into the fan while going down the road. You can feel around in there (with the engine off of course and in neutral) by turning the gen/alt and touching all the vanes in the fan for debris

Would a vacuum with a thin nozzel with or without a tubular probe help getting into the fan area ?

You might want to attach a screen that's made for your fan shroud to help prevent that from happening.

Ernie:

There are four small bolts holding the fan to the fan shroud.  

Remove the fan belt (keep all of the loose washers on the nut side of the pulley and replace them behind the nut when re-assembling everything).

Remove the metal strap holding the alternator to the stand below it.

Remove the four bolts holding the fan to the fan shroud.

Remove the fan.

You should now be able to look down inside of the fan shroud to make sure you get everything out of there.  Just be aware that you may end up pulling the fan shroud off of the engine to get any melted dynamat off of the head fins, but, if you need to, it should be relatively easy with the fan removed.

You should be able to easily clean everything off of the fan.  Heat, carburetor cleaner, acetone - what ever works to get that stuff off of the fan blades and make them squeaky clean again.

Put everything back together.

Good luck.

OH!  And get a screen to go over the fan inlet opening as Dave mentioned, to make sure this doesn't happen again!

x2 what Gordon said! You may have to remove the screws/bolts (10mm) on each side of the shroud (lower portion) in case you need a little more wiggle room to remove the fan/alternator for inspection. 

Remember that if you have internal air direction vanes inside of the shroud, they are activated by the bellows thermostat below the engine on the passenger side.  There is an actuator rod that goes from the thermostat up between the cylinders and attaches to one vane.  To remove the shroud, you must remove the thermostat bracket, remove the t-stat from the bracket and then unscrew the t-stat from the actuator rod (it's just threaded on).

Only then can the fan shroud be removed.

If, OTOH, you don't have a t-stat, then remove the screws holding the shroud down (there may be several, depending on who assembled your engine and what tinwork is there) and lift it up while angling the top progressively towards the rear - you must get it up over the oil cooling tower within and that sticks up about 8"-9" from the top of the case on the driver's side of center.  Lane's pulled his a few times and, while not easy-peasy, can be done by a newbie.

All that said, a newbie could pull the entire engine (a Craftsman Motor/ATV jack makes it super easy) in 2 hours at most, clean everything up and put it back in - like an all day Saturday job.  You'll STILL have to get the shroud off to do a proper job of it, but I would start by just pulling the fan out to see how much you have to clean up.

OH!  And don't put Dynamat (or anything else that might come loose) onto your firewall.