A method of modifying the activity of a solid acid catalyst by contact with a carboxylic acid is presented. The modified catalyst is exposed to a feed mixture including olefins in a reaction zone, and an effluent including an isomerized olefin product is withdrawn from the reaction zone. The isomerized olefin product includes a more random distribution of internal olefins than the olefins of the feed mixture. The feed mixture and the isomerized olefin product include linear olefins. The isomerization results in no more than about 10 weight percent additional branched, compared to the olefins of the feed mixture, among the olefins of the isomerized olefin product. The isomerized olefin product includes no more than about 20 weight percent dimer. The olefin monomers of the feed mixture and the isomerized olefin product include from about 4 to about 30 carbon atoms. The effluent includes no more than about 20 weight percent ester. The solid acid catalyst may be an acidic ion exchange resin. The feed mixture may include olefins, esters, and carboxylic acid.