can't this boat go any faster??

[ranman6]

I have a 1995 Merc. Sport Jet 120 hp.

Last year after a new re-build I put it in the water and it ran fine all season, this year it was a little sluggish at frst and now its gone down hill it wont get over 15 mph, before i have had it up to around 35-40. The only thing I have done different is changed the brand of spark plugs from champanion to NGK........could that be it? Also I haven't been running as high as octane as usual.........could that be it , or should I look else where?

Thanks for any input.

 

[frozenokie]

Re: can't this boat go any faster??

I have had similar effects from changing spark plugs - especially if your motor manufacturer recommends Champions. I found that running NGKs in my Evinrude makes it run like crap even though the plugs look fine when pulled afterwards. But that's been my experience with them. And for Octane - of course higher octane fuel will produce better performance. Make sure to use "no ethanol" fuel if possible too. If ethanol fuel, by reports, makes it run more poorly, then your performance is just that.

Just a thought - I have ran a Merc sport jet 60HP up north and found that I need to check the intake before every outing and sometimes during. They really suck up alot of stuff that will get wrapped up inside the housing and clog it up.

Change those things you changed back to what you were running. That would definitely be the first step in diagnosing

 

[reddogg]

Re: can't this boat go any faster??

I'd say go back to the champion plugs for a start. I have an evinrude and I went from champ to ngk and it ran like crap, found the right champs, put them in and ran great. Dunno what the diff is between the plugs but I can't dispute the results. Also, have you looked into the usual suspects? Carbs, fuel pumps, etc...?

Red

 

[Bamaman1]

Re: can't this boat go any faster??

Funny thing, most good mechanics will tell you to scrap the Champions and go for NGK or other brands. Unless you're using 100% gasoline, everyone really needs to either use a gasoline treatment or drain their tank for the winter. 10% ethanol just separates too fast, and causes carb. problems.

I'd also be quick to check the pump for obstructions. You're just losing too much speed.

 

[wicked251]

Re: can't this boat go any faster??

I have a 120 sport jet as well, always pulling weeds from the intake. That makes a huge difference.

 

[ranman6]

Re: can't this boat go any faster??

I am trying to find a set of Champions and I have checked the grate, seems ok.
I need to check the carbs, but need to find a flush kit so I can run the boat in the driveway, does anybody know which one I need and where I can get one?

Thanks for all your help.