I have a '73 Merc 1500 'Tower' I bought last summer. I went through the whole fuel system first then new impeller, fuel line & pumps, plugs, normal tune & clean, ran in the dark, cle aned carbs twice, etc. It is on a 17' Checkmate and was stored the last 8yrs or more. I have 120psi +/- 1lb compression on the starter for all cylinders (& 5lb water pressure). I have read here it should be 125+, unless my tester is off. Checked timing to Merc manual and everything else I had tools for. <br /><br />It would not go over 4000 rpm@40mph in the water with a 19 prop. Acted like it had a rev limiter. Otherwise ran great, no surge, bog, miss or anything. Tried 17 plastic prop with same results. I figured it would over-rev and need 21 prop, but no(according to tach). <br /><br />Took it to a dealer this spring for a dyno run. They said it is good on dyno, and ran it on the water to find problem. It did 4000 rpm thing and they said I had the wrong difuser on the prop(MI wheel from them)and it needed a Merc 21 they put on. They reported 5400 rpm and run nice. I have yet to test it, but how could the small prop lower the max rpm to 4k? The manual says prop for max 5800 rpm on an empty boat. What gives with this? <br /><br />I also put in a new tach & speedo since the stock tach read the same but was boucing around. Also new rectifier to make this alternator tach work & get voltage right. Is my tach way off? 
The previous owner swears he saw 64mph+ from this boat with an unknown SS prop, I figured it had low hours and maybe 60mph for the size & type boat. Thanks for any suggestions, and the fantastic site.
The previous owner swears he saw 64mph+ from this boat with an unknown SS prop, I figured it had low hours and maybe 60mph for the size & type boat. Thanks for any suggestions, and the fantastic site.