[protowdriver1]

I am about to purchase a boat with a 2000 mercury 90 hp ob on it and i cant seem to find what the compression should be. If anyone can help then that will be awesome. Thank you in advance.

[hkeiner]

The specific level of compression is less important than making sure the compression is similar on all cylinders. Compression gauges are often inaccurate as far as the specific compression level shown on the gauge but they still work fine for comparing compression between cylinders. Having said that, if your gauge shows compression over 100 psi on each cylinder and the variance between highest and lowest compression is less than 10 psi, you should be OK. Search the FAQs and other forum posts on compression checks, as it is necessary to do the compression check the right way to avoid damaging ignition components.

This is my experience anyways. Others may have additional or better suggestions.