No reverse and other issues

[OneMoore]

Hello everyone, this forum has been a big help for my build and just wanna say thanks!!! Now on to my problem/questions. I have a 2003 Ez Go TXT that I put a 18hp Briggs in and I was having a problem with the cart trying to take off everytime I sarted it so I figured my belt was too tight. So I went ahead and moved the motor back some more to losen the belt and no my problem is the motor builds RPMs for a sec and then takes off like a bat out of h#$!. What am I doing wrong here? Is there an exact measurment from center of drive clutch to center of driven clutch when installing a big block? DOes it have to be that exact?

Next question. I've ran the cart about a dozen times trying to get the bugs worked out of it and the reverse has worked great every time. Tonight I hopped on it to go cruse around and NO REVERSE! the cable seems to be moving up and down freely so I dont know if I broke something internaly or is there something I don't know? Thanks in advance for the help.