Hi all, I have a 2007 sherco 300. Do you need to warm the engine up after start before you sellect a gear, because  when I started mine then about  1 minute  later I selected 2nd gear and it shot off

Some bikes tend to get stuck clutches when sat for too long, take the bike for a slow put around for a few minutes working the clutch in and out and giving it small feeds of throttle and they will unstick. Happened to my kids KX65 last week for the first time ever for me.

If I read you correctly; your clutch sticks on cold startup and needs to be broken free before you have clutch action.  That is a function of your clutch plates and the lubricant you selected, not so much a 2-stroke engine operating temperature thing as your transmission oil viscosity is regulated by the environment.  example: if you are riding in sub-zero temperature your transmission oil might never get hot.  

... going to guess you are using a multi-grade engine oil in your transmission.  I rarely to never have a clutch stick issue running ISO 46 UDT hydraulic fluid, even in sub-zero weather.

For safety sake, you should always be prepared for the clutch to stick initially by off-weighting the rear tire and applying the front or rear brake when you first engage the gear.  It should break free almost immediately.

Its a very common beta problem. Either try putting in gear and rocking back and forward with clutch in before start it to free sticky plates. Or be ready for it to move off when put it in gear but ride for a bit with clutch in until it releases. If its stood a while hopefully it will  ease as its used more

Sticky clutches on trials bikes are a thing - I usually get the bike running, hold the clutch in, roll it forward and drop it into 1st and then keep running with the clutch in until it frees off (can take a minute for some bikes if they've been sat a while).  As always, switching to Dexron 3 ATF gearbox oil either cures or eases the problem.

 

As for the bike setting off, yes any modern 250 or up is going to do that - that's part of the reason people who are new to trials can learn easier and faster on a 125 or 200.

Two more thoughts re cold stick, based on Beta ownership:

My Beta 4T had really bad cold stick. I used to put the front wheel against the wheel of my car, hold in the clutch and kick it into 2nd. Sometimes I needed to bump weight down onto the rear wheel to get it to release, otherwise the wheel just spun.

After trying various oils, I found Putoline Nanotech was the best for both cold stick and progressiveness. I never tried ATF though, that some people recommend.

 

If you look in the Beta section you'll find a thread on the fix, Sherco & Beta share friction plates until Sherco changed to the diaphram clutch. Basically the fix involves removing the excess glue between the friction pads

My 2007 Sherco 250 does the same thing when it has hasn't been ridden in days or weeks. Seems to be a European trials bike problem for bikes without diaphragm clutches. Japanese bikes with basket clutches don't have this problem. My old Fantics had sticky clutches.