Merc 100 hp Hard start.

Old merc 100 hp, engine #2930983 . Starts good and then may run good for a while and then dies all of a sudden. Pulled coil wire and fires as soon as u hit the starter and the quits firing while engine is spinning. Sometimes will run for 30 min. and other times will quit firing and will not start at all. no fire again. Need help.

Re: Merc 100 hp Hard start.

Your Merc 1000 SS has electronic ignition which requires a constant +12V on the red terminal of the ignition switchbox (on the right-stbd side of the motor). With the ignition switch in the ON or START position, +12V is also supplied to the white terminal on the same side of the switchbox.

You can measure power on those terminals with a meter or test light. It's common to have a bad ign switch or a broken wire in the control harness cause this sort of problem.

Try wiggling the harness and all associated internal wiring while checking for power on the red and white switchbox terminals.

You can also unplug the external harness and check for power to ground, on the correct pins. With the control harness disconnected, you can also check the motor's internal wiring for continuity. Recommend if you're going to do this, to disconnect the red & white wires at the switchbox, for more accurate readings.

Here's a link to a wiring diagram for your motor:

http://www.maxrules.com/oldmercs/Wiring/1966ona/32.jpg

A last-resort kind of troubleshooting tip is to connect +12V directly from the battery, to the red and white terminals. You should have spark as long as they're connected to the battery.

Just a word of caution, never apply power to the other side (left-port) of the ign switchbox where the distributor connects. You could damage the distributor and/or switchbox.

Let us know what you find and if that doesn't narrow down the problem, there's a good test procedure for the entire ign system. Next likely suspect: the trigger inside the distributor.

HTH.............ed

Re: Merc 100 hp Hard start.

Thank you very much for the quit response. Will check wiring as soon as it quits raining. The wiring diagram was great. thank you. If it turns out to be the trigger, as the wires from the dist to the box had all the insulation off them and had to be taped up, how much does the trigger cost, and is it still available. How hard is it to replace. Can u tell me what year my motor is? Thank you.

Re: Merc 100 hp Hard start.

Your motor is a strange one to find out what year it is.... maxrules.com oldmercs.com are two sites with info and it looks to be a 1969 according to maxrules.........are you sure it is a 100 hp model and not BP unit or some other hp ? Maybe someone changed the wrap/faceplate so it reads 1100. Many lakes have hp limits and people just swap out the wraps to circumvent the law.

Re: Merc 100 hp Hard start.

Maybe it's an "8" not a "9", according to this model/year guide the '69 1000 had a serial # range of 2484633 to 2836018:

Mercury 2-takt, R6, 6-cyl, 80 - 150 hp, produktions?r, modellguide

The only other models I could find within range of the "28......." number are '70 800-4 and '70 1350-6. Either someone played mix-n-match with the center section (exhaust tower), or mix-n-match with cowlings.

A few pics would help us figure out what you've got. Especially one of the Stbd (right-hand) side, since it'll show the configuration of the intake transfer port covers, which is a dead giveaway betwen 90-c.i. Sixes and 99-c.i. models.

The distributor triggers between the 2 models work the same electrically, but are way different physically, so we do need to pin down the style of ign for sure. A pic of the distr. will definitely help.

Cheers.........ed

Re: Merc 100 hp Hard start.

The number was right on the motor. here are some pictures, the trigger is bad, the wires are broken real close to the trigger. This trigger is horse shoe shaped, not a circle like some are. Maybe this will help. Do u know where i can find a new trigger for this dist. and what it will cost Thanks, Joe

Re: Merc 100 hp Hard start.

I have these two plates and don't really know which one goes on this engine.

Re: Merc 100 hp Hard start.

Many of those triggers are NLA from Merc

CDI Electronics does have a source for many triggers however if I remember they come as a distributor assy.

Re: Merc 100 hp Hard start.

Fortunately, even though the trigger assy is NLA from Merc, there are some kicking around still, because this style of trigger was also used on some Mercruisers.

The part number is 393-2918A 6, and there's another number out there, 393-2918A 9, which should be the same style trigger but I'm not sure if it's physically identical to the 100hp trigger. I suspect it'll work but you'd have to compare to be sure.

Here's an aftermarket trigger, it ain't cheap!

Mercury Trigger R393 2918 393 2918 | eBay

Looks like CDI Electronics may be able to repair your part, you'd have to contact them for details and price:

R393-2918: Premier Repair Service

This guy has the "A6" trigger which is the exact crossover for yours:

Mercury Quicksilver Trigger Assembly 393 2918A6 | eBay (you could get yours rebuilt for less).

This seller has the "A8" trigger (which was superseded by the "A9" trigger):

New Mercruiser Trigger Assy 393 2918A 8 | eBay

Cheapest at $200 for a new part, the seller is a marine dlr so you could probably ask them about the interchange between the "A6" and "A8/9" part number.

This ign was also used on a '67 50hp and 65hp models, also on the '68-'69 125hp.

Never know, you might find a whole parts motor on Craigslist, start searching!

BTW, just a last thought, before you spring for very expensive electrical parts, it'd probably be a good idea to do a compression check (if not already done), so as not to throw good money after bad.

HTH................ed

Re: Merc 100 hp Hard start.

And double check all tests following the CDI Troubleshooting Guide

CDI Electronics Practical Outboard Ignition Troubleshooting

Remember, there is NO RETURN on electrical parts.

You want to be certain that the parts is defective before your spend a bunch for another one.

Testing is a LOT cheaper than parts, PROVE the fault so you can order only what you really need.

Re: Merc 100 hp Hard start.

Thanks, Guys, I will check with CDI Electronics and see what they say. Did not know about them and they are only about 50 miles from me. I go to Huntsville all the time shopping.

Re: Merc 100 hp Hard start.

Soldiered the wires on my old unit and now it fires good and doesn't go dead. Doesn't idle good sometimes, was missing while cruising about 30 mph and i replaced spark plugs and that seems to have taken care of that. Do u know where i can get a diagram of the carbs, this engine sat up for years and i think i will clean the carbs and see if that will fix the idle. Also who has carb kits.