I thought I'd post this in case anyone else has the problem / does the same thing.
I have a 7.5m M4 Turbo twin Cam that is my most used sail.
For a few years now I've had the boom cam pop off occasionally. I 'assumed" it was because the sail was getting old and stretched and adjusted things to get it better.
I put in a lot of spacers , added downhaul ( over the years it eventually went to 2 extra stops) and added batten tension. This worked in that the cam stayed on but the sail was over down hauled , flat and gutless. The boom cam looked very knuckled over.
I used it yesterday and found it very heavy and exhausting to use. I blamed my lack of fitness.
Anyways.. I got Mike and Pete to look at it yesterday . Low and behold I had SDM cams on a RDM mast! 
A few years ago I'd swapped all my sails from SDMs to RDMs. I must have overlooked the Turbo as it's my 'freeride sail. 
Today I changed the cams to RDMs and adjusted spacers and batten tension and I have a new sail! Thanks guys,.
It now has a lovely deep belly, good profile and I can downhaul to specs.
I can hardly wait to use it . It should be much more powerful and light to use.
So don't assume..it stopped me from looking further.
While we are on the subject of mismatched cams I've also experienced the other.
I bought a new Mach4 - 5.5m sail. At that time I was using SDM masts but I didn't notice the sail came with RDM cams.
I sailed across to the other side of the lake and had to actually sit in the sail to get the sail to rotate! That's when I learned that Severne RDM cams are 4mm longer than SDM. Swapped to SDM and everything was ok. 
All a learning experience.
Select to expand quotepowersloshin said..
I managed to foil with my foil mast back to front, but only once !
I think that trumps me.. although I persisted for years..
Turbo seems sensitive to the right amount of downhaul. A bit less than optimal, and the bottom one pops out.
Even when optimal sometimes.
After talking to a Severne rep, I was told that it needs the correct mast. I use a NP mast - apparently too soft for the sail.
Turbo has been replaced by Moto?
3 cams now. It would be interesting to hear from Moto users.
Select to expand quoteObelix said..
Turbo seems sensitive to the right amount of downhaul. A bit less than optimal, and the bottom one pops out.
Even when optimal sometimes.
After talking to a Severne rep, I was told that it needs the correct mast. I use a NP mast - apparently too soft for the sail.
Turbo has been replaced by Moto?
3 cams now. It would be interesting to hear from Moto users.
For sailing in chop I prefer the Turbos.
I replaced my 7m Turbo with a 7.2m Moto. It's pretty good and I imagine it has better control in the top end but the wider luff tube can fill up and it's heavier to uphaul as a result. It's better for shallow water speed sailing if you've got enough wind.
The luff tube isn't as wide or as bad as an Overdrive or Mach but a bit more than the Turbo. That's a big issue for me as a lightweight weakling..
I feel it's bottom end isn't as good as the Turbo but I may not be rigging for that it as well as I should.
Select to expand quoteObelix said..
After talking to a Severne rep, I was told that it needs the correct mast. I use a NP mast - apparently too soft for the sail.
It is not the stiffness but the bendcurve, the Neil Pryde ones are softer at the top and stiffer around the boom height, compared to Severne masts. I would recommend to get the correct severne mast first, before buying a second severne sail to use on the NP mast.
Going from a 7m to a 7.2m you have added 0.2m of sail.
It does not sound like much but the swing weight will be apparent.
I tried a 6.5m Mach proto the other day and straight away it felt much bigger than the 6.2 Severne race sail i previously owned.
Much more physically demanding. The sail itself felt good but the extra 0.3 metre made the sail feel a lot heavier.
Going any bigger than 6.2 to 6.3 i start to enjoy the sport a lot less.
My 6.3 i use 430 total luff length. The 6.5 had a luff length of 460.
Shorter luff lengths for a given sail size i think help to reduce the physicality of sailing as the power is closer to your body.
Select to expand quotePcdefender said..
Going from a 7m to a 7.2m you have added 0.2m of sail.
It does not sound like much but the swing weight will be apparent.
I tried a 6.5m Mach proto the other day and straight away it felt much bigger than the 6.2 Severne race sail i previously owned.
Much more physically demanding. The sail itself felt good but the extra 0.3 metre made the sail feel a lot heavier.
Going any bigger than 6.2 to 6.3 i start to enjoy the sport a lot less.
My 6.3 i use 430 total luff length. The 6.5 had a luff length of 460.
Shorter luff lengths for a given sail size i think help to reduce the physicality of sailing as the power is closer to your body.
You obviously get more wind where you live..
Select to expand quoteObelix said..
Cams not popping out?
With the correct mast and matching cams I've never had issues with cams popping off. RDM mast and cams give great rotation but I'm a lightweight.
