Need Help 1997 Mercury 75hp

[Clivey]

Hello,

Well I have a 1997 Mercury 75hp outboard and last weekend a friend and I were on a fishing trip. It was the first time I had the boat out this year. The first day I had a ruff time getting it started but when it got running it ran fine all day. No problem restarting or running. The next day I had problems starting it again. Once I got it running and got away from the docks it wouldn't run any fast than 6 mph at full throttle. Normally it goes 32-34 mph. If i would let it idle for more then 10 seconds it would stall. On the lake I took all three spark plugs out which i just put new ones in three days before. The top plug was very oily the bottom to were normal. At that time I put three new spark plugs in, got it started again and it did the same thing. On the way back in to the dock the motor would occasionally speed up jerking the boat like it wanted to go. When we got it trailered I pulled the spark plugs out again and the top one was the only oily one again. Well I thought I might have a bad wire or coil and it wasn't firing so we tested it and I get spark. Does anyone have a clue what the problem is or any suggestions. I sure could use some help my grandpa trys to help but the motor is a little to new for his motor knowledge. Thanks for reading. Clive

[thefairlaneman]

My guess is it is a fuel flow issue. You may want to use some carb cleaner (seafoam) in the gas first. By the way you have found a good forum for about any boat problem . The mods here are helpful and very knowledgeable too.Welcome aboard!

[dalton565]

hey i have exactly the same engine as you mate only 1999. First thing i would do is check ur fueling, speaqe the primer blub and check for leaks. Then drain each of the 3 carbs by taking the drain plug out of the bottom of each in turn and letting any water/fuel run out.

Make sure you disconnect the fuel line and let the engine run until it runs out of fuel before attempting this as fuel will run eveywhere.

Use some carb cleaner to clean them once disconnected. I be pretty sure ur issue is one of these though id suspect its ur carb, esp if it hasnt been done in a while. A little water in them will cause problems.

[Clivey]

So I tried everything above and got nowhere. I found out that when I take it out of gear and run in full throttle it runs normal but when it's in gear and I go full throttle it bogs down sometimes dies. I don't know what else to do. Please help if you can. Thanks Clive

[Clivey]

I have tryed everything. The local boat shop wants $120. just to look at it and tell me whats wrong. They call it a tune up. I know it needs more than a tune up but I don't want to pay $120. to find out that it's another
$800 and I can't afford it. If anyone has an idea let me know. Thanks Clive

[MaggieRose]

Clive,

Look at the bottom of your carbs, should be a brass hex head screw on each side. Take them out and LOOK through. You should be able to see from one side to the other. The main jets are located just inside each of the screws you pulled. If any of these main jets is gummed up, your engine will act just like yours is acting now.

If any of the jets is plugged, you should pull the carb or carbs and clean them. If pulling them looks like a big job, try spraying the ports with carb cleaner, let it soak and hit them with some compressed air. Each jet will come out (threaded) so you can clean each on on a bench, but be sure you put them back in the way you took them out!!! The jets are made of brass, so don't use any steel wire to clean them (jets can get dirty a again real fast if they are scratched).

[Clivey]

If the main jets are gummed up would it run at high RPMS out of gear? It only bogs down when in gear.

[DsevenEm2]

have you checked spark? are you sure you're not just running on one or two cylinders? causing it to bog/stall/run roughly? are u sure you dont have water in your fuel tank?

[Clivey]

I checked the spark when I first started having this problem and every thing was fine there. The gas tank was empty from last season and I added new gas. I have added seafoam to the gas and still no different. The motor runs fine out of gear at high and low rpms. But when in gear anything over idle it bog down.

[bhile]

If your serial no. is between 9793577 - 0P016999, rebuild your fuel pump. Be sure to get the kit from a Merc dealer so you are sure to get the new type check valves. According to a Merc TSB, ethanol causes the old rubber type check valves to curl up on the edges and not seal properly.

[kennyboater]

im having similar problems on my older smaller merc. i was just at my local mechanic and they said that with a clogged carb, out of gear it may rev like yours does because it is not under any load. but when it is under load, it will bog down.

if it were me (as im doing right now) i would pull the carbs, and clean/rebuild them using a manual. if you just pull the high speed jets, it may have some crud else where in the carb. if you clean/rebuild the carbs it will probably run fine

just my experiance so far,

btw, i took my carb apart for the second time now and found that there is gas in my float causing the carb to flood; meaning that there must be a small crack in the float somewhere. so your problem may be something as easy as cleaning/rebuilding the carbs.

its not to hard or expensive with a manual to do yourself. just start with the carb that you think is the problem