78 mercury 700 hard start and won’t stay running

I inherited my uncle’s 82 blazer bass boat 2 years ago, and have only recently been able to try and use it.I feel like I should point out that this is my first boat, I haven’t heard this motor run in nearly 20 years, and I haven’t been around many 2 stroke outboards in probably 15 years I took it to a local outboard repair shop last summer to have the carbs cleaned, and replaced the battery and fuel tank. Was having some wiring issues with the trolling motor so it’s been sitting for almost a year. Finally got the trolling motor straightened out over the weekend and decided to get it ready for summer.

Tried to start it in the yard to make sure it wasn’t going to leave me dead in the water on my first time out in it. Long story short, because this is my third attempt to post this, it took forever to start and would only run throttled up for a minute or two. Would jump and stutter like a stick shift car taking off in third gear above 1/4 throttle in gear. Checked the plugs, #3 looks like it’s never even fired, but is getting good spark and looks wet with fuel. Can someone point me in the right direction, I don’t want to miss another summer because my boat is out of commission.

Spark test a must. Please remove all plugs and check for 7/16" or better nice white/blue spark. Probably the culprit. Then we can guide you with some diagnostics to determine which components will need replacement. Got some sharp techs here to help.

To start it lift the cold start lever halfway, pump fuel bulb until it's hard, push and hold down choke button - turn key to start position. After 20 years sitting I think the fuel pump needs rebuilding. Don't exceed 2500 rpm in neutral.

Hate to say it, but if # 3 plug is spotlessly clean you might have water getting in there from a bad lower seal or a cracked block.

Try this: Remove and ground the # 3 plug wire and fire her up on the other two, then reconnect the plug wire. If it runs better disconnected with # 3 disconnected, that's the problem.

Jeff

Do you have more information from the shop? Why was the tank replaced? Did you ask them to get it going, or did they say it was all set to go? Quicksilver, it may not have been sitting unused that long, but the OP said he never heard it run for that long....perhaps Uncle was still using it. Did the shop test compression? Need that report plus spark test report.

OK jumped too quick to a conclusion.

Tank was replaced because it was an old steel tank that was rusting out. Replaced with a 6 gallon plastic unit. My uncle died in 96, left it to my grandparents who used it to fertilize the public lake they ran until about 3 years ago. I don’t know if the shop did a compression test but getting good spark on 2 and 3, no spark on 1, swapped plugs 1 and 3 ,still no fire on cylinder 1 hot spark on 3. Compression seems fine but I don’t have a gauge to measure it

It might be a coil problem, swap the Nr. 2 coil with the Nr.1 (make sure they're both connected and plugs grounded) here's a wiring diagram that says the lead on the back of the coil must be grounded, you can check this when swapping:

Caution: Merc used two firing orders on those engines (1-2-3 and 1-3-2) so make a sketch of where the wires go BEFORE moving anything around. Note also that the top coil's ignition wire goes to the bottom cylinder (and vice-versa).

Jeff

The 1975-78 manual shows 1-2-3 for both distributor and ADI ignitions [but this is for the 650 there was no 700 listed so it must be a later model], the best way to make sure is look on the water jacket it should be marked there. And use the serial Nr. to date it exactly.

It was made apparent to me the switch box was not covered in black caulk and has in fact had a meltdown. I feel like an absolute idiot for not realizing it sooner. Want to make sure I’m getting the right thing when I replace it. Part number is 3325524, but I am under the impression they are using a different part number to replace it, 1147778. Is that right?

Have you have verified it with Mercury (dealer) they know the supersceding Nrs.

Mercs # is 332-7778, CDI # is 114-7778 and the Sierria # is 18-5775 which I suggest

Lots of new ones on E-bay, cheap. If you pay more than 50 bucks for a new one you didn't search enough.

Jeff

I’ve seen them starting around $30 going up to near $350. Appreciate the help fellas and will update when I get it replaced. Thanks all

Just be sure to buy a NEW one--lots of them for sale, cheap. (Why? Merc sixes used two per motor, which helps availability.)

Jeff

Never buy a used one ….most off blown motors and bias usually damaged