Just after a few tips.

I've ordered some new engine mounts, as the engine felt rather loose in the frame. I've managed to change the front ones without too much hassle, however the bottom rear are posing problems. I removed the bolt which goes through the side stand, and the allen screw thing from the RHS. However, I cannot get the rubber mounts to come out.

Maybe removing the rear upper mount would allow me to move the engine around in the frame somewhat, but undoing that looks like a huge job. It needs to be done, however, to replace that rubber mount. So far, I have removed all of the fairing. I am wondering if I will have to remove the rear swing arm or subframe to make access possible? I cannot remember what I did last time when I had to remove the engine, that was three years ago!
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MC21 Honda NSR250. TYGA 300 conversion.

If memory serves me correct (on my mc18):
You will need to remove the top engine mount, the short one with the allen bolt. You need to be able to drop the rear of the engine down low enough to get at the mounts. It s the rubber insert with the steel sleeve and the two rubber cap/washer thingies on each end. Then you can get at them. You don't need to remove the shocks/subframe, let the engine pivot on the front mounts, it won't drop all the way out because it hits on the frame. You will need to remove the exhausts if you haven't done so already. (I assume you have). A reminder, the top rear engine mount rubber - steel cap thingies are difficult to fit, there is not enought room to fit them with the engine in place, so if you drop the rear and they fall off, you will need to hold them in place with tape of grease or something when you lift the rear of the engine back up. Hope this helps!

Thanks for the info.

We've been at trying to get the mounts out for over an hour now. We've removed all three bolts going through the engine, however, it will not drop down far enough at the back so that we can remove and replace the mount rubbers. Can't see how to get it out any further...

Is there a way to do this without completely removing the engine (and carbs, radiator etc.) from the frame?

Just cannot get those bottom engine mounts to budge.

Sorry if you already know this.
They are meant to pull out from each side of the engine. Don't try to knock them through towards the middle of the engine.
They shouldn't be very tight. Can usually just push with your fingers, grabbing them underneath the engine.
If they're tight, you should be able to use a wooden drift and mallet to gently tap them out. Because the MC21 lower mounts are two-part, just locate the drift on the inner end of one mount under the engine.
If they still won't budge, and you're changing them anyway, you'll have to use a bit of squirty lube and a set of grips to twist the bleeders to free them.
Grip them on the tubes under the engine. Just be careful not to damage the cases!
Good luck!

That's right, Chester.

Today I had my Father helping me on the bike. Where a lesser man would have given up trying to pull them inwards and reassessed the situation, looking for another angle of attack, my Dad persevered and was able to pull one out the wrong way. Totally destroyed, doesn't matter though, as we are installing new ones. So, a bit too late

You suggest removing them the correct way, which is what I intend to do. The problem is, how do I get them out the correct way? There is no room between engine and frame to remove them! I can't seem to get the motor any lower in the frame...