Can I still make the section 167 HST election if only some of the business assets are being sold?

Possibly, but it depends on what "some of the assets" actually means in your deal. The election under the Excise Tax Act is available where the buyer acquires all or substantially all of the property needed to carry on the business, or a clearly identifiable and separately operable part of the business, as a business. If what's being sold is genuinely a distinct part of the business — a division, a separate location, a separable product line — that can still qualify, so long as the buyer is acquiring essentially everything needed to run that part on its own.

Where this breaks down is when the assets left out are actually necessary to operate what's being sold as a going concern; leaving out something essential, like key equipment, customer contracts, or the lease for the operating location, can mean the sale doesn't meet the test at all, even if most of the value changed hands. There's no fixed percentage that decides this on its own — it's a qualitative assessment of whether what's being sold can actually function as a business in the buyer's hands.

Because getting this wrong exposes both parties to an unexpected HST assessment, confirming the specific facts against the test with an advisor before relying on the election is essential.