115 I-6 lack of power at altitude, smoking

[dka1ser]

Hi all, I am new here, but not new to boating. I am an avid fan of my 1977 Glastron CVX-16. It has a 1977 Merc I-6 115hp. I bought it from Minnesota and live and boat in Denver, CO around 5-6000 feet asl. <br /><br />I did an exhaustive search in this forum regarding high altitude adjustments and think I have the right idea. It only turns 42-4400 rpms 41mph (GPS) with anywhere from 17 to 23", pitch props. It used to get 5000rpm and 50mph in MN. <br /><br />1) Is there anything else I should do besides re-jetting the carbs? It stumbles on acceleration sometimes and idles rough, but runs good at speed. <br /><br />2) After idling or running "no-wake" speeds for more than 5-10 mins, she smokes like a bandit upon take-off back to planing speeds for about 2-3 mins. Is this related to the running rich condition and can be solved with re-jetting? The plugs are not carboned up, but are oily after shutting down. <br /><br /><br />I have a series of repairs to do over winter, and want to have a good season next year. I plan on a water pump and fuel pump rebuild, come spring plan a "Seafoam" decarbing, and spending a day on the lake fine tuneing it come spring. Any other suggestions? <br /><br />Appreciate all the knowledge here and hope to contribute where I can. I previously had a 70hp 3cyl Merc and a 85hp Johnson. <br /><br />Regards, <br />Dennis

 

[Clams Canino]

Re: 115 I-6 lack of power at altitude, smoking

You DO need to rejet the carbs for the altitude.<br /><br />then go through the idle mix screw adjustment as per my timing and sync post here.<br /><br />-W

 

[dka1ser]

Re: 115 I-6 lack of power at altitude, smoking

Thanks, I assume that ordering a Mercury shop manual from mercurypartsexpress.com for my outboard will assist greatly in this jet swap and all other matters? Do you recommend a particular repair manual?

 

[emckelvy]

Re: 115 I-6 lack of power at altitude, smoking

According to my Seloc manual, your motor should have .068" main jets for your area. Sea-level jets would be .072".<br /><br />You probably have .092" vent jets (the externally visible jets atop the float chambers). The recommendation is usually to remove these vent jets entirely, as they lean out the mid-range. However, since you are already running too rich, maybe the thing to do would be to leave .092" vent jets (if you have that size) in.<br /><br />The recommendation for vent jets at your altitude is .088".<br /><br />But, this would lean the motor out perhaps too much, especially with leaner .068" main jets.<br /><br />Of course, maybe someone has already pulled the vent jets out; at your altitude, no vent jets combined with sea-level main jets would exacerbate your rich condition. You'll find it runs a lot crisper when properly jetted and you'll regain a lot of your lost rpm.<br /><br />BTW even the 5000 rpm it was turning in MN is too low and you should rejet, then re-prop to obtain at least 5500 WOT with the boat lightly loaded.<br /><br />HTH.........ed