If it is the later carb, 1993 ish on, then it could be an air leak from the throttle butterfly shaft, I have known this a few times, try spraying a little wd40 or similar around the throttle shaft, if the engine note improves, and becomes smoother, then you have an air leak, that is air being drawn in where it shouldn't.
The reason the engine note improves is that because the wd40 is flammable the engine finds this better than normal air, where as the air alone means the mixture is too weak to burn.
Also this kind of leak usually only affects the cylinders near to it, so the other cylinders may sound fine.
Also worth checking is the inlet manifold gasket, I had one of these leak on number 4 cylinder, but on the underside, boy did that take some finding.
It may be one of the many ( Too Many !! ) air hoses that these carbs have, either split or just loose enough to allow air to be drawn in.
Sometimes these leaks improve as the engine warms up, mainly due to the expansion of the manifold , which can then mean the leak is much less.
Missfire on start up can be head gasket, but you should see water loss, but not always, as it could be a very small leak, so on a day to day basis, not much water/coolant is escaping, but it may be just enough to make the spark plug wet, and once it warms up the plug dries out and all is well.
Hope this helps,
Regards Rascalvan (Tim)
www.bedfordrascal.com
