Can i go a tire size bigger on it? it came with 16-7-7 front and 16-8-7 on back can put 18-7-7 and 18-8-7 on it? The original fronts are hard to find

 

Check the clearance between plastics and tyres, remember clearance alters when suspension goes down, and check on full lock at the front. If it looks like you have still got over 1" now, 2" bigger tyres are not going to foul. Acceleration may drop a bit though.