Any off the shelf leak down tester available for Yamaha RD400 ?
HVC and Economy sell them. Cheaper one looks out of stock and the other option is pretty pricey.
Search ebay for Banshee leak down.
Hardware store stoppers for the carb boots, thick rubber blank gaskets held in with the downpipes on the exhaust, couple fuel tees from auto parts store, fuel pump/vacuum gauge from Harbor Freight. Carefully press it up to 6 psi with your compressor regulator backed all the way off of a tire hand pump.
https://www.toolsource.com/upper-engine-tools-c-468_849/motorcycle-timing-gage-for-14mm-plug-size-p-124984.html?tsqtid=928030
Best price I was able to find shipped to HI. Mainland buyers have more options though.