Hi, I have a mercury black max 135hp either a 90 or a 91 that is acting up. It starts fine and reaches top speed fine but after 10 or 15 minutes of running it starts to lose speed. With a tuber or skier it runs fine for only around 5 minutes then bogs down to just a crawl. It has new spark plugs and we've used a bottle of sea foam on it. we are a long way from home without the manuals, thanks for any thoughts or suggestions.
