i just got a 1983 xj650 every now and again it revs really high for no reason(bit scarey when riding)itook carbs off and noticed the inlet rubber mount was worn and cracked inside,any ideas how to repair it and would this cause it to rev up or could it be somewthing else,in need of some help of you clever people please

toss 'em.

get new ones.

you would want a repair compound going in to the combustion chamber.

Here is something to consider.

Manifold Repair

Auto zone and ace hardware has that stuff cheaper than $8.90