15 hp merc 1994

Author Message   Dan Member Username: dshffer Post Number: 10 Registered: 04-2008 Posted on Thursday, June 19, 2008 - 06:54 am:    I have bought a used boat and motor. it is 1994 15 hp. Mercury, 16' alumacraft boat. took it out last night after a a week of getting ready, (impeller change, thermostat, and new plugs/wires. It starts great, idles fine, and runs ok, but my problem is it doesnt seem to have very much top end. it doesnt seem like it is running at high enough rpms at wide open throttle. Seems like at 3/4 throttle all the way down it doesnt change the rpms. Could this just be a out of adjustment carb or bigger problem? Everything else seems to be fine except the top speed. My other motor i had was 9.9 johnson and it just seems to me that the johnson had more push than this new motor. thanks for any help DAN   JB Senior Member Username: beckerjs Post Number: 1075 Registered: 11-2005 Posted on Thursday, June 19, 2008 - 09:01 am:    wrong prop? need max rpm   Graham Lamb Senior Member Username: galamb Post Number: 3434 Registered: 05-2007 Posted on Friday, June 20, 2008 - 11:16 am:    Dan, own 9.9's and a 15, have swapped them back and forth on the boat under different conditions, fiddled with props, foils, grades of gas etc. I currently run an 11 pitch 4 blade cupped on my 14 footer when loaded light and switch to a 3 blade 10 1/2 pitch in middle of the summer and/or when pushing more weight, even drop down to a 9 pitch 3 blade. Bottom line - there just isn't a whole lot of difference - best I came up with was about 2.5 mph more out of the 15 (but that may have been a bit of a fluke). The one noticable difference is the 15 burns way more gas. On a 16 footer I would expect you to be turning an OEM 9 pitch or maybe an 8 depending on the total weight you are pushing. As to how the throttle acts - your observation is what I am used to. From the time you hit max timing (about 3/4 throttle) to the rest of what's left I rarely see a noticable difference in speed (unless wind speed is zero and you are cruising across glass like water) and only then it's measured by the gps and not anything you can really feel - mind you the combined run time on my 3 motors is in excess of 5000 hours and the youngest one is 17 years old so their compression is just a touch off from factory spec I would suspect that you may get 14/15 mph, best scenario, out of that rig - if that's about what you are getting, that's about all she has got to give you.....   Dan Member Username: dshffer Post Number: 11 Registered: 04-2008 Posted on Friday, June 20, 2008 - 05:14 pm:    thank you graham. I am taking it to shop tommorrow maybe I am missing something adjusting the carb but just to be sure ill let him look at it at least. Have had really bad luck with outboards in past few years and just wanting to be sure. have been stranded a few times and dont wnat that to happen again. Thanks for your advise. I really need it sometimes!   Dan Member Username: dshffer Post Number: 12 Registered: 04-2008 Posted on Monday, June 23, 2008 - 07:19 pm:    just a quick update. got new prop this weekend, carb adjust, and off to lake we go. everything ran great. the prop was same as was on there so maybe it was slipping or something. The motor ran like a brand new one this whole weekend. ran about 3 hours saturday and about 7 hours sunday. only used about half a tank for both days, does this sound right? water was pretty choppy both days also, saturday was about 2-3 footers and sunday was about 2. No huge concern as we caught fish all day both days. thanks for all your help and insite.   Graham Lamb Senior Member Username: galamb Post Number: 3503 Registered: 05-2007 Posted on Tuesday, June 24, 2008 - 09:56 am:    Dan if you are saying that you played around for 10 hours and burned half a tank (6 gal tank?), that would be doing very well. Running her wide open you should burn about 1.5 gallons per hour, at 3/4 throttle (max timing, where the trigger linkage stops moving but you still have throttle left), you would burn about 3/4 gallon per hour. I find I can run canals (7 mph speed limit) for about 20 hours on a 6 gallon tank of gas and consider that pretty decent (17 year old 15 horse Merc/Mariner with over 1500 hours on it)...

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