I'm just wondering what causes boost spike?

My 2 wheel drive Cosworth sometimes spikes the boost up under load It's hard to describe but in higher gears it boosts up 1.3 bar and blows out the spark I don't mind a spike as long as the boost comes down to the preset limit if you know what I mean.

I re-gapped my plugs to 0.6mm because they were gapped at 1.1mm and it still did it and I've now fitted a Group A coil but I haven't tested the car yet.

My car now has a -31 actuator on it and it holds 1 bar/15psi nicely but sometimes it spikes and you have to back off and then apply the throttle again, it also did this as standard with a standard actuator.

Would adjusting the actuator rod either way control the spike? I thought that it would but I wanted to check before adjusting anything

This afternoon I am going to check the vacuum hoses and make sure they are all tight etc but I want to make 100% sure the car is A1 rather than just trying to get around the problem.

Sorry if this post is hard to understand

Thanks