New to Boats and going Broke... 2-stroke merc 115 bogging

[OSU Doc]

New to forum and to boating. Bought a 1975 fiberglass Baja with 115 merc end of last season. Mechanically inclined but in uncharted territory. I am having trouble getting a 82 mercury 115 thunderbolt 2-stoke to pull a wakeboarder (3 foot pylon installed). I switched from a 22 pitch 3 blade to a 18 four blade both stainless. Sank some $$ and didn't fix the problem. It has worked great a few times with people of same size water conditions... and then started bogging on acceleration with the next rider. Runs great with no load until i get it angry trying to get her going ( I'm not too hard on it... can't afford to blow her). Then clears up and runs great. It is a light boat and has performed like a champ. I need consistency in my hole-shot! Planning on checking compression, plugs, and adding seafoam. Carbs cleaned and plugs changed less than 30 hours ago, but last season. I left fuel in it over winter (bad idea right). Thanks for the anticipated help!!

 

[Chris1956]

Re: New to Boats and going Broke... 2-stroke merc 115 bogging

I would be surprized if you could have pulled a 'boarder with that 22P prop. The 18P prop is much more in range, but depending on size of boarder, actual motor compression, hull type and weight, it may be marginal.

Try to get her set up to run w/o a boarder. Prop it to hit 5500RPM with usual load.

On my inline six Merc, I could pull a skiier easily with a 21P prop. With a 23P prop, I couldn't get above idle with a skiier. Ran OK w/o a skiier, though.

 

[OSU Doc]

Re: New to Boats and going Broke... 2-stroke merc 115 bogging

You had a merc 6... GREAT! Help from the Supreme Mariner! I'm new at this whole boat thing but loving it... besides the hole in my student pocket. Very good mechanically though just trying to work through this rough spot. I know it has the power. And it has performed flawlessly. Only to fail 10 minutes later. I've thought of all the stupid stuff pretty sure. Fuel mix or splash, trim changes, prop, and the like. A little help from a seasoned veteran such as yourself would be much appreciated! I'm thinking maybe carb adjustment. It idles a little low. Not sure how confident I am in the tach but with 3-4 adults on the 16' and the 3 blade 22 it was about 4200 with the 4 its 4800. Don't think prop is the problem. It idles a little low though 700 maybe. Gonna check compression. Got my fingers crossed I bought a decent motor. With no load she runs great on plane... We're moving!

 

[79Merc80]

Re: New to Boats and going Broke... 2-stroke merc 115 bogging

You weren't listening, the prop IS at least one of the problems. You are overpropped. The RPM's should be as close to 5500 as you can get (Maybe even a little over) with you, fuel and equiptment.

 

[OSU Doc]

Re: New to Boats and going Broke... 2-stroke merc 115 bogging

Took it out today. Got up my friend 160 and myself 175. Little lag out the hole, but when it hit it was assertive. Ran some seafoam. And skipped the compression check when I realized #3 plug wire had fallen off from my tinkering the last time... I'm not beyond stupid mistakes (nor is anyone who I have ever encountered). A little afraid to check compression. I hate bad news... Still only running about 5100 rpm with moderate load respectively. I have the option to switch this prop tomorrow. I really am not convinced that this one isn't sufficient. But I only get one chance to exchange. Any thoughts? I'm thinking that maybe the carbs where a bit dirty as well. It sat with untreated fuel. Too many sick and needy toys not enough time.

Is using cold start to clear motor for a few seconds bad??

 

[Gomer50]

Re: New to Boats and going Broke... 2-stroke merc 115 bogging

Never use cold start (starter Fluid) Starter fluid removes all the oil needed to lubricate your internals.Remember it's a 2 cycle motor.I am with the pitch reduction Idea.Better to rev in the mid to upper 5000 RPM'S @ Wot.

 

[Chris1956]

Re: New to Boats and going Broke... 2-stroke merc 115 bogging

Gomer, I hope he is referring to the cold start lever. If so, we all need to do it from time to time.

 

[OSU Doc]

Re: New to Boats and going Broke... 2-stroke merc 115 bogging

Yes. I was referring to the cold start lever. From what I understand this advances timing and increases throttle. Shouldn't hurt to use this function to clear motor after idling before launch... Right? Also. I understand these motors are made to run at relatively high rpm. However, towing or running sustained at over 5000 rpm just doesn't seen prudent for engine longevity. I'm a car guy. Four stroke and large displacement are a different animal but I want this motor to last as long as possible. Would it be better to reduce pitch and increase RPM or run lower rpm the majority of the time (around 4000) and occasionally put some stain on it pulling up boarders? Has anyone run similar setup? The 22 pitch 3 blade was kinda standard it seems. I dropped 4 degrees pitch and added a blade already. With a light load I am willing to bet it already goes over the 5500 limit.

 

[Chris1956]

Re: New to Boats and going Broke... 2-stroke merc 115 bogging

Prop it to run 5500 with average load, and then use it any way you want. Those motors can run wide open or part throttle w/o any issue. Make sure you use fresh fuel mix @50::1, and change the waterpump impeller every couple of years, as necessary. Change the gear oil every fall. I usually change it midseason as well, but it likely doesn't need it.

 

[OSU Doc]

Re: New to Boats and going Broke... 2-stroke merc 115 bogging

Thanks for the advice. Gonna give her some attention and try that prop one more time. Still have the opportunity to exchange for a 4 blade 16. I just have to see how it goes. Thanks again.