MERC 70 HP TROUBLES

[auto]

Hi I have a 1978 70hp merc outboard, I've rebuilt carbs, new tanks, fuels lines, primer bulb, de-carbed engine, checked compression, (135psi on all three cylinders) ,new plugs & have spark at all cyclinders, ajusted carbs more times than I can count.<br /><br />My reaccuring problem is it's hard starting cold and warm, When it is running in neutral it seems fine(sometimes) or at WOT it is also good, when I put in forward gear, it stalls immediatly or if I try to punch it a little to get going it bogs out and stalls.<br /><br />Perhaps I'm not ajusting carbs correctly? I don't know? any help would be appreciated! <br /><br />Thanks,

 

[Chris1956]

Re: MERC 70 HP TROUBLES

Auto, First of all those motors are normally hard to start. You need to choke them very well, and crank them very fast.<br /><br />Your second problem (bogging on acceleration) is typical of the carbs being incorrectly adjusted. I recommend you open the top carb misture screw 1/8 of a turn and see try to accelerate. If it accelerates smoothly, the carbs are correctly set. If not open the bottom carb 1/8 of a turn and try again. Repeat sequence if necesssary, top carb first. These motors idle best when the carbs are set too lean for them to accelerate. The correct adjustment is when the motor will idle decently and accelerate well.

 

[auto]

Re: MERC 70 HP TROUBLES

Chris1956<br /><br />Made ajustment, however the motor still dies as soon as it is put in forward gear, then is hard to start.

 

[Chris1956]

Re: MERC 70 HP TROUBLES

Auto, The carbs should be relatively easy to adjust close enough for satisfactory performance. I think you should start from scratch. Make sure your spark plug wires are not arcing, put a timing light on each wire to observe that they are sparking consistantly and check your timing and synchronization. When this is all good, set the carbs to 1-1/2 turns from lightly seated and start the motor. Warm up the motor and adjust the idle mixture screws until you get a fast smooth idle. This will likely be too lean for the motor to operate in gear. Try it in gear, and if it dies, open each mixture screw 1/8 turn and try again. When it doesn't die in gear at idle, try to accelerate. If it is not smooth, open mixture screw on top carb 1/8 turn and try again. If still will not accelerate, open lower carb mixture screw 1/8 turn. Repeat as necessary.<br /><br />If this procedure fails, there is something else wrong on the motor (flooding carbs, air leak in intake or crankcase, ignition problems...).

 

[SeaHorse]

Re: MERC 70 HP TROUBLES

Look at the carb to block seal. You should be able to see the gasket all around. It's easy to have the gasket slip down down on one side when you're trying to put the carbs on and this would let air leak in behind the carb. Be sure the bottom carb is opening when the throttle is opened. If not, the little blade is missing that connects the top and bottom carb. During carb rebuilt I assume you put in the new style white plastic floats with new needle and seats and adjusted the float height according to the package. <br />Try pulling the plug wires off one at a time while it's running. If you get a poke, or if the motor doesn't slow down when a wire's off you know that cyl has an ignition problem.