[] They give CG as 25 to 35 percent but what is the best starting point. if I take 25 to 28 percent I have to put a lot of weight in the nose to balance it

What airplane and what is your flying skill level?

Nosehevy is safer than tailheavy. A nosehavy airplane's controls will be a little "sluggish" A tailheavy airplane will be excessively touchy.

Its bettr to add the weight (as far forward as possible) to get the forward balance point for test flights...then adjust moving the balance toward the rear by removing weight. If you start off too far back... you won't get the opportunityto adjust it... you'll just have the opportunity to fill a garbage bag.

What I would like to know is what is the best percent of the cord to start with 30% 35% or 1/3

For a typical engine in front... large main wing, small tailplane in back design.... The best place to start is 25% if you have no other guidance. Starting back at 30% to 35% without knowing how a particlular design responds to the rearward CG is dangerous.

Better... read the plans and put the CG where the plans say it belongs. its a SAFE starting point. (you can almost always move it back some as you get used to the airplane.)

Never go behind 37% unless the design REALLY has a lifting tail. (then you'll be back around 60%.... but its a whole new ballgame in how to trim the model.)

As FH asked already, what is the plane and what have you flown previously??

If you're building your first 3D kit, but have flown 3D for awhile now, then 30 to 35% might be okay. If you're talking about your first or second plane, then 25% is almost a must!
Dennis-