Merc 1986 115 Problems..

[mercuryverado]

I've got 3 things I need to figure out:
Idle speed
Surging
Bogging

I have checked all the carbs, replaced bad fuel lines, rebuilt fuel pump, installed new spark plugs, determined spark was good, timed, linked, and synced. My prop is a 3 blade Turbo SST, turing 4950 WOT on my CV-16. I have experienced the hesitation/surging out of the hole as I'm accelerating. It seems like if I give it wide open, it will go away. The bogging issue usually only happens with a load. If I have a load, I have to move the throttle forward EXTREMElLY slow in order to plane out. With the idle, it seems like I'm about ready to loose a gear case. In the water it's 1200. When I put in gear, it slams down to 800, then idles just fine. Our ski team uses OptiMax's on our Hydrodynes that idle at around 700 all the time, in gear or not. Is that something just with newer engines? Any insights would be appreciated.

 

[CharlieB]

Re: Merc 1986 115 Problems..

Lean cough, bogging, and hesitation of acceleration under load are classic symptoms of too lean idle mixture.

Idle speed is adjusted with idle timing, retard timing from where you have it now to slow the idle speed.

Adjust idle mixture to best idle speed while IN gear and on the water so that engine is at idle load. Once mixtures are set to best idle, further open the idle mixture screws 1/8 turn to provide the additional fuel required for acceleration. Test by slamming the throttle to WOT. If ANY bog or hesitation then open each idle mixture screw just the width of the screwdriver blade slot and retest WOT acceleration again.

Repeat to perfection.

Once finished then make your final idle speed adjustment while in gear using the idle timing set screw.

Done.

 

[mercuryverado]

Re: Merc 1986 115 Problems..

I'll look into the idle speed. I am running a 21 pitch prop. Do you think a 19 would get me out of the hole faster and revving higher RPM's? Here's a YouTube video of my bogging problem pulling a barefooter: http://www.youtube.com/watch?v=-0xAzjDheMY

 

[starcraft1982]

Re: Merc 1986 115 Problems..

I would suggest getting the motor running properly before you start worrying about prop changes.Id pull the carbs and clean real well and then adjust as stated above.Also,i would check compression as running lean can kill a motor in short order.