It should be an 12N 12A-4A battery
According to WikiAnswers, the proper battery for a Maxim 400 (the Seca's sister) is 12N 12A-4A. I'm looking for one also. This is the same battery I used in my '72 Yamaha XS650 although it had a "-1" designation at the end.
try the yamaha seca store.
Try one off of a yamaha seca 400
If there is one it will be located from the main fuel line running from the petcock to the carbs.
it's behind the right suspension bar. it's a black allen tip.
ebay
Yes, a round headlight will fit on a Yamaha Seca. Just be sure that the model and specifications match what will fit into the mounting brackets.
81hp
2
The spark plug gap in a Yamaha Seca is 1/2. It can be easily obtained and is very affordable and likely to be replaced by the owner. It is a quick replacement.
There is NO WAY a stock Seca 2 will do 140. About 115-120, which isn't bad.
the difference is the Yamaha is better