few problems still after head replacement

[WARRIOR72]

hi guys me again
im sure you remember i replaced my head/gaskets/bolts etc etc, i still have a few problems need ironing out!!
when starting i wait for the beep of the glow plugs and start..engine starts and runs fine for about twenty seconds then begins to misfire,if you rev the engine its very lumpy and a lot of grey/black smoke comes out which didnt happen before!this will eventually clear and itll run fine but the weird thing is if you stop it and then start again itll go back to running lumpy and smokey again until you rev the engine and it clears again!!the exhaust gasses smell like unburnt diesel, and ive noticed a considerable drop in acceleration/ mpg (was doing 21 now down to 16) and top end (was 95 mph now down to 80!) could this be down to bad injector spray pattern? or im thinking maybe the diesel pump one tooth out or jumped a tooth maybe?ive squirted carb spray around the injectors and inlet manifold and cant notice any leaks/change in idle when i do this! also i had problems with it over pressurising again,replaced the new thermostat with old one and is fine... new stat was only 3 weeks old!! any ideas/advice apreciated (ps ive bypassed the primer pump housing temporarily as when i bled it i noticed diesel coming out the top and thought it might be sucking in air from there but its still the same!)
cheers guys

[BUSHWHACKER]

hi guys me again
im sure you remember i replaced my head/gaskets/bolts etc etc, i still have a few problems need ironing out!!
when starting i wait for the beep of the glow plugs and start..engine starts and runs fine for about twenty seconds then begins to misfire,if you rev the engine its very lumpy and a lot of grey/black smoke comes out which didnt happen before!this will eventually clear and itll run fine but the weird thing is if you stop it and then start again itll go back to running lumpy and smokey again until you rev the engine and it clears again!!the exhaust gasses smell like unburnt diesel, and ive noticed a considerable drop in acceleration/ mpg (was doing 21 now down to 16) and top end (was 95 mph now down to 80!) could this be down to bad injector spray pattern? or im thinking maybe the diesel pump one tooth out or jumped a tooth maybe?ive squirted carb spray around the injectors and inlet manifold and cant notice any leaks/change in idle when i do this! also i had problems with it over pressurising again,replaced the new thermostat with old one and is fine... new stat was only 3 weeks old!! any ideas/advice apreciated (ps ive bypassed the primer pump housing temporarily as when i bled it i noticed diesel coming out the top and thought it might be sucking in air from there but its still the same!)
cheers guys

After a run, remove the fuel filler cap and listen for a hissing sound. If it hisses, then the fuel tank breather is probably blocked and causing a vacuum preventing smooth fuel delivery.

[plumb bob]

You may want to recheck your glowplugs, just to make sure they are all working correctly.
They are, apparently, supposed to coninue heating for a while after the engine starts, to continue to warm the bore/fuel until relay shuts them off totally.

It could also be, as you say, the fuel pump timing, so check all your t/marks are all correct.

Also check all the vaccum pipes are fitted correctly, I think the enrichment device, associated with cold start workd from these.