Jib problems

I would check the rig settings before you do anything else, bat speed is key to get foils working pointing to high to early i find almost stalls boats but i ont sail a 420, is the jib sheeted corrctly it is possible to over sheet, reading more of your later post suggest spreaders are different on each side or the mast is bent!

The foils are spotless, never had a crash except once when the crew messed up the jib sheets. Yeah theres a few 420s at the club one went to worlds so ill compare the theirs for the shroud position. Its not that we're pointing too high, we'er on more of close reaches than beats, we are basically going across the lake while the rest are going up. It also only seems to happen on port so that may suggest to me that we're being stupid and the shoud position is different on one of the sides making the mast bend to that side, would that effect it?

420s don't point very high. Should sail with the inside tell tale lifting. Definitely below the average angle of a handicap fleet.

The whole set up of the boat, from mast rake to board position has to be though about if its a problem in a 420fleet though. Jib trim is quite crucial. Barber hauler in some conditions makes massive differences, there are quite a lot of various tuning guides around on the web. It does depend a lot on the sail, if its vibrating it sounds old, and a new less stretched sail will point higher. Letting off the jib cunningham flattens the entry which may help. Lowering the jib on the luff wire will allow you to sheet harder without having too closed a leech.

I think you are asking the impossible here

A little more info such as  what kind of vibration, whole sail, luff only, age of sail, rake, rig tension etc may help the knowledgable cast thier wisdom