Hi there
I had a very annoying and peristent misfire in my 2.25 petrol. I can share with you what was done to solve it. I checked everything I could but in the end I took it to a Land Rover specialist to have a look (Howe Engineering in Hertfordshire)...He set the timing using a strobe (which was way out, despite my thinking it was correct, by setting the static timing), set the points gap (I know not relevant if you've got electronic ignition), repaired a loose connection to the coil, took the head off the carburettor and gave it a top end service/clean, and at the same time tightened the exhaust manifold which was blowing. He also checked the spark plugs gaps but I think these were ok. All perhaps obvious, but I think much easier if you've servicved and fettled dozens of Series land rovers like the chap who worked on my vehicle.
This solved the misfire and it now runs very well. I don't like to give up on a problem, but I'm not sure I would have solved this alone...
Perhaps start with the carburettor?
Good luck.
Agree with all this except I would say leave the carburettor until you have done all the more easy to check bits, i.e. tappets, spark plug gap, (even though you changed them the gap may well not be correct for what you want as they come out of the box), also make sure everything in the distributor moves easily and is unworn, that neither of the advance springs is bust stretched or missing. If the carb has a vacuum advance check by sucking on the end of the pipe that the diaphragm is working and actually advances the timing. (If there is no vacuum, then I apologise for my ignorance.)
Once you get it running, even if you do not have a strobe, you can time it quite well by turning up the tickover until it runs pretty fast, say 2000 rpm? Pretty loud but at least all the advance should be in, then turn the distributor back and forth noting where the revs drop at each end of the movement, then put it to the middle of that where the revs are highest. But it is best if you can get hold of a strobe.
Once all this is done, buy a rebuild kit for the carb if you can. If not then at least strip it down and clean it without inserting anything in the jets. Blow thorugh them with an airline preferably after using carb cleaner to shift the gunk.
Ensure the float needle valve is working properly, again blowing through the fuel feed pipe and moving the float to check it stops the flow and then allows it to flow again. Then you can make sure the float level is where it should be, bending the tab if necessary to get it to where it should be.
Once you have put it all back together again, get it running adjust the tickover so it will tickover! then tune it according to whatever procedure is recommended for the carb. They are not rocket science, most of the time!
But it is true that leaking manifolds will cause thios problem. you can test for this by spraying the maifold with WD40 or carb cleaner or Eazistart. If there is a leak the engine will rev up as it "breathes in" the stuff you spray on it. Then you'll know to get the manif off, sort it out and replace the gasket.
Best of luck.
Oh and make sure the rotor arm is OK.
