80hp Mercury outboard post-rebuild adjustments...help!

1979 80hp Mercury Outboard I4 complete rebuild, bored over .015...new stator, trigger, switchbox, rebuilt carbs, new inline fuel filter. I have 132lbs in each cylinder and spark at each spark plug. I can get the motor to start and idle fine and even rev up high out of gear. Once in gear, the motor will rev up through primary pickup until the secondary pickup is supposed to occur. After secondary pickup, the motor just boggs down. The manuel says to adjust idle mix screws out to get a hole shot, but after 5 turns out, no dice. What am I doing wrong? I am running 25:1 oil per manual for 10hour break-in. The timing seems set right, at least at wot is 27degrees. Any idea where to go from here?

Re: 80hp Mercury outboard post-rebuild adjustments...help!

did you get the linkage in sinc...the timing advance moving when you throttle up?

Re: 80hp Mercury outboard post-rebuild adjustments...help!

Do you have a Merc Service manual? The aftermarket ones have issues with their accuracy.

I think you will get advise to retard max timing to 23* BTDC or maybe less. Today's fuel is not too good.

Usually idle pickup timing is set at a particular degree setting when the carbs are just about to start opening. Idle timing is ususally less than idle pickup timing. I don't know idle pickup timing spec for your motor offhand.

Carbs need to be clean and set to 1-1/2 turns open from light seating. In practice, the final setting will be closer to 2 turns open, but you need to adjust a bit rich it to give smooth acceleration.

What kind of boat and prop do you have? If too much prop or too heavy of a boat, motor will not rev up.

Re: 80hp Mercury outboard post-rebuild adjustments...help!

First of all--Thank you for your time gejandsons and Chris1956, I really appreciate it.

The carbs are in sinc., and yes the timing arm moves with the throttle arm. I started the motor with the two arms pretty close, kept her running and adjusted the primary pickup where the throttle plates barely start moving. I am working out of the merc shop manual, also have a seloc, but they are pretty close to the same instructions. Anyhow, the merc manual says to start by setting carb idle/adjust screws to 1.5 out from light seat, then put in gear and adjust idle stop screw to where the primary pickup almost moves the throttle plates, then with timing light adjust primary pickup screw (which moves the timing) until it reads between 5-8degress btdc, after that move throttle to wot and set spark stop screw to read with timing light 27degress btdc. If im reading the manual right...the spec at idle out of gear is between +2 and -2, idle in gear is between 5-8btdc and max is 27.

The boat is a 16' skeeter and motor is original to the boat. 3 blade prop is original to the motor. I rebuilt the motor due to a loss of compression in #1. (had 90psi, with other 3 at 120psi...rings worn out)

Do you think the over bore would change timing at all? Also, I had to start the idle screws out from seat closer to 2 just to keep her running to make these adjustments. My thinking was because its .015 overbore?? Could the secondary jets in the carbs be plugged??

I was thinking my next steps should be to dunk carbs again and also check for any air leaks in the fuel hose/filter...what are your thoughts?

Thanks again.

Re: 80hp Mercury outboard post-rebuild adjustments...help!

OK, I have dragged out my old grease covered Merc Manual.

Did you set/verify that the timing pointer is set accurately? I use a caliper to measure to top of piston crown and then add .464 and back off the piston and set the pointer.

OK, Remove spark plugs 2-3-4 and tape them together, ground them to the block and install the plug leads. Put timing light on top cylinder. set throttle so the carbs are fully closed, but the arm to open them is just touching them. Now crank motor and observe timing light reading. Adjust the primary pickup adjustment screw (screw A just up a bit from pivot point on throttle arm)until the timing light reads 2-4* BTDC. Tighten screw

Now advance throttle all the way to full. Crank motor and adjust spark advance stop screw (screw B at top of throtle arm) so timing light reads 27*BTDC (I would recommend 23* BTDC, however). Tighten screw.

Now adjust throttle stop so the stop is hit, before the carbs stop opening due to hitting their stops.

Install spark plugs, fit flusher and start her up. Adjust idle RPM screw (idle stop screw is another name), for 800RPM or so. You may need to adjust throttle cable barrel nut as well. Put the boat in the water and adjust the idle mix screws to allow smooth acceleration and reasonable idle. A good idle usually means carbs are set too lean.

Hope it helps

If that doen't get it, suspect carbs are dirty or floats/inlet needle/seats are bad. Your boring oversize will have no effect on carb jets or other settings.

Re: 80hp Mercury outboard post-rebuild adjustments...help!

Okay...this sounds great. I was pretty confused about the whole process for finding and setting tdc and the pointer .464 and -.464.

I figured to just pull the #1 plug and rotate the engine until the piston comes all the way up, set the pointer for 0. This would be tdc in my mind. I have a dial indicator, but cannot figure how to use it as illustated by the manual. Can you further explain how you use a caliper for this process please?

Otherwise, I understand everything else and I will try it!

Thank you for your time! I cannot tell you how much I appreciate this!

Re: 80hp Mercury outboard post-rebuild adjustments...help!

You can use a caliper or even a ruler. Use the depth measurement on the caliper. Set the piston to TDC using a screwdriver. Now open the caliper and stick the end of it into the plug hole. Read the depth to the piston top, and add .464" to it. Now back the piston down to match the proper depth, and see where the timing pointer points. Adjust as necessady.

Re: 80hp Mercury outboard post-rebuild adjustments...help!

Alrighty Guys,

That did it. My timing pointer was off by only 1/2 inch! Yeah, that might make a difference when your trying to get the timing right! Made the pointer read right and timing it was a breeze with your instructions Chris1956. Runs great. Thank you so much.

Re: 80hp Mercury outboard post-rebuild adjustments...help!

Glad you got it.....

Re: 80hp Mercury outboard post-rebuild adjustments...help!

that was a good thread, good luck with that engine

Re: 80hp Mercury outboard post-rebuild adjustments...help!

I have a very similar problem with my 1987 Mercury 60 hp, can someone tell me what the timing adjustments are for my motor? are they the same as for the 80 hp.

Good post & reply. Thanks Chris. Its fortunate I found this, even if its several years old its verified more clearly your recent reply that helped me with my 1978 80 hp old Merc issues. BTW I was able to succeed in getting it running properly after the new parts & lynch etc Only After discovering #1 New Coil of 4 New Coils right out of the box Was Hit & Miss Sparking & Timing Light Showed it. It Even Passed the coil wire switching between #1 & #2, the Ohm & DVA voltage test checks! BUT Only after physically switching it & timing light showed it, then it was revealed! Talk about surprised! strange! I don't really feel I should express my feelings here about China Built CDI Parts, as reiterated by many others & marine mechanics; you may know what I mean
Regards
Steve