merc problem

db77 · Jun 2, 2009

Hey guys, new to the site...lots of info so far! I have an issue with my 1977 mercury 70hp outboard, it will run/idle great on the muffs, and idle great when in the water, but when i put it in gear it dies almost instantly. I dont know where to begin, it has good fuel, new plugs...and im about to clean the carbs soon...has anyone ever ran into a problem like this before?
Thanks alot in advance!

dbcrue · Jun 2, 2009

Re: merc problem

my 77 merc 150hp did the same thing it was the distributor was out of sink. it wasnt advancing fast enough.i messed withmine and got it close then it went to the mechanic and he fixed it .he said i was on the right track. So that might be something to look at.Im not a pro just a shade tree guy.Hope it helps

db77 · Jun 2, 2009

Re: merc problem

will for sure look into it, its a good start for me, i have no idea where to begin as of now...thanks alot!

Showtime22 · Jun 2, 2009

Re: merc problem

My first boat did that. It was a 70 Horse Merc. It drove me so nuts I sold it without fixing it. But knowing what I know now I think I should have checked the neutral safety switch. It kills the engine for a tic to allow the gears to disengage.

Goodluck

moorecomp · Jun 2, 2009

Re: merc problem

Showtime22 said:
My first boat did that. It was a 70 Horse Merc. It drove me so nuts I sold it without fixing it. But knowing what I know now I think I should have checked the neutral safety switch. It kills the engine for a tic to allow the gears to disengage.

Goodluck

The neutral safety switch will not kill the motor, it only prevents the energizing of the starter solenoid if the shifter is not in neutral. I has no connection to the ignition circuit. Go for the timing fix.

Craig Moore
Mancelona, MI

jbrown270 · Jun 2, 2009

Re: merc problem

assuming that the timing is correct and the carbs are clean, you might try setting the idle mixture screws to their base setting. Too lean of a mixture at idle will cause the motor to die instantly when put under a load.

AMD Rules · Jun 3, 2009

Re: merc problem

jbrown270 said:
assuming that the timing is correct and the carbs are clean, you might try setting the idle mixture screws to their base setting. Too lean of a mixture at idle will cause the motor to die instantly when put under a load.

I'd agree. Start with turning the idle mixture screws out another 1/4 turn and see how it runs.

Never a bad idea to double check timing as was also suggested. Base timing can effect hole shot dramatically. That said, it doesn't sound like you working on a hole shot issue, but rather the simple fact that it stalls at idle going into gear.

Neutral switch is not a likely candidate here.

Showtime22 · Jun 3, 2009

Re: merc problem

My bad. I think I meant the shift interrupt switch.

db77 · Jun 3, 2009

Re: merc problem

Ok, i'll get a list going and do all that and check them off...headin out now to get wrenching...thanks alot for the ideas guys!...Also, is there anywhere i can get info on the timing of this motor, or how to go about it without making it worse?

CharlieB · Jun 3, 2009

Re: merc problem

Don't be so much in a hurry to mess with parts that are not the problem.

Before you mess with the timing at all, look to see if the timing linkage moves throughout its range of motion with the throttle lever, if it does, then LEAVE IT ALONE.

Dirty carbs are the most common cause of ALL engine problems, clean them SPOTLESSLY, blow thru ALL passages.

Carefully, just barely seat the idle mixture screws, then back them out 1 and 1/4 turns, start and warm up the motor, adjust idle mixture to BEST idle IN GEAR while ON THE WATER, then back the idle screws out an additional screwdriver blade width. Slam the throttle wide open in gear, any hesitation, bog, or lean sneeze, then back the screws out just an additional blade slot width, retest the sudden WOT.

Once ALL traces of hesitation are gone, relax and enjoy a job well done.

db77 · Jun 4, 2009

Re: merc problem

Well i just got inside from messing around with the boat, went to fire it and nothing!...come to find out my neutral safety switch AND ignition switch is bad, where can a guy find parts for these old gems at? Thanks alot!

Moody Blue · Jun 5, 2009

Re: merc problem

You have a host of problems it seems, which are not related.

The neutral safety switch has nothing to do with stalling when put into gear. It merely prevents the starter solenoid from activating if the controller is in gear.

What leads you to believe the ignition switch is bad? Again, not likely related to the stalling issue. I do know that if you have the original MerControl type box, the wiring is likely to have deteriorated inside the box and can cause problems. I just finished stripping mine and replaced all the wiring. The choke button and ignition switch were fine once I got them cleaned up.

db77 · Jun 7, 2009

Re: merc problem

i know there not related, but i went to fire it and nothing would happen, i had no voltage out of my ignition switch to the neutral switch so i made a jumper and hooked it up to the other side of the neutral switch and it fired off, also the switch does no change state no matter what, i think the contacts are shot in it.

Showtime22 · Jun 7, 2009

Re: merc problem

You could try cleaning all the contacts in the switch with steel wool or a scotch brite pad.

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