Mercury 65 hp has power loss

[yorel]

I recently bought a 15 tri-hull with a 1976 Merc 650 3-cyl, 65 hp, SN - 4385748, type 'C' carbs. The ad said 'MOTOR NEEDS WORK'. Truth in advertising! I am new to boats but not new to keeping things running. (four kids in college, broken cars daily event). I have rebuilt the carbs, new float needle and seats, set timming and sync acording to 'SELOC' repair manual. checked compression, 135/135/135 psi, checked plugs and spark, fuel pump and filter, looked for plugged exhaust ports, etc. The problem is that I can get it to start, idle and rev nice out of the water with muffs on, but when I take it to the local 'pond' it is hard starting, won't idle smooth, and dies on rev up. Its like the added back pressure on the exhaust when it's in the water makes it a whole different beast. I have tried pumping primer bulb while running but makes no difference. I am begining to suspect a weak ignition system, but hate to start replacing expensive components on trial and error basis. The stator and trigger assemble bench test good, but can't find info on testing switch box. Does 11/16 float drop and 1 turn out on idle screws soound right? Also, what about the reed block? 'SELOC' repair manual is vague about it. Any help would be greatly appreciated, as my wife wants me to finish the kitchen remodel project first, I told her I got priorities!!! Might be sleeping in the boat soon!!

 

[graddy]

Re: Mercury 65 hp has power loss

When you are setting the idle mixture screws are you doing that when the engine is on the hose or in the water with back presure. The coorect way to set them is with back presure on the exhast, either in a run tank or in the lake.<br /> Start with the mixture screws 1 1/2 turns out from a lightly seated position. Start and let the eninge warm up in gear. With engine running, slowly turn the idle screw counterclockwise untill the cylinder starts to load uo due to an over-rich condition. Next slowly turn screw clockwise untill the cylinders fire evenly and engine picks up. Countinue turning clockwise until too lean a mixture is obtained and engine slows down and misfires. Next, set idle scew 1 to 1 1/4 turns counterclockwise from to gian true setting. Remeber too lean of a condition can cause damage and also can cause a hard start. If engine hesitates durning acceleration its to lean.

 

[sharkcat]

Re: Mercury 65 hp has power loss

What DTS said except with the mixture screws turn them anti clockwise 1/8 turn at a time pausing about 20 secs between each 1/8 turn till the motor runs rough note the position.Then turn the screw clock wise the same way until the motor slows/runs rough note the position of the screw the correct position for the screw is mid way between the 2 noted positions.Repeat for the other carbs.Start at the top & work down you may have to repeat the process to get it perfect.Sleeping in the boat will be a cheaper option in the long run but it gets lonely & cold

 

[mtmiller]

Re: Mercury 65 hp has power loss

I own a newer version of that engine ('89 60). It sounds like you've given it some good thought and have some ideas/leads. Both outboards I've owned had to be tuned with backpressure (in tank or in water) like the others have said. Try that first.<br /><br />If that doesn't help, check a couple things. I wonder if tilting/transporting your motor has something to do with this. Make sure the bleed lines and check valves are functioning properly. They tend to get gunked up. Also, if your motor has one of those tilt switches (a mercury switch which shuts ignition off if engine tilts too high) disconnect it. I had intermittent issues with one which drove me nuts (more). Third, check the restrictors under the intake cover (if your engine has them - mine does). They tend to fall out over time and can make tuning a real chore (happened to mine). Finally, make sure the carbs are synced to the timing lever properly. Most outboards control idle speed with ignition timing first, then carb butterflies. If the carb pin which rides on the plastic cam wears (or both), the relationship between timing and throttle opening and idle speed can get all messed up (I know this the hard way too). If it is stalling out with backpressure you may need more ignition timing and less throttle to achieve a given idle spec.<br /><br />Chew on these things for awhile... good luck!

 

[yorel]

Re: Mercury 65 hp has power loss

Thanks every one for info, will continue to chase down problem