Mercury 7.5 takes forever to get started

Hi All,

My first post here.

For starters, I have a 7.5hp Mercury Outboard 4 stroke engine. From the serial number, I *believe* it's an '81.
The boat and motor have been sitting for quite a while (maybe ten years or more.) The motor was kept in a garage so everything in it is nice and clean.
To freshen it up, I rebuilt the carburetor and replaced the needle and seat, as well as put a new impeller in it.

After getting everything put back together, I brought the boat and motor out to the lake and put it in the water. It took quite a lot of pulls to fire it up, but once it did the motor ran great and skirted the 14' aluminum boat around the lake nicely. I just figured the difficulty starting was due to the fact that it'd been forever since it had last fired up. I took it around the lake
and back. Thought all was well.

Brought it out again and, again, it took forever for it to fire up. Then, when I was a mile or so out on the lake, I stalled the motor and had to start it again. My hands were bruised from how many times I had to pull the cord to get it to fire (probably 50 - 100 pulls over a duration of 20 minutes). There was no catch, no sputter, no trying from the motor to get it to start. I tried different choke settings, tried adjusting the throttle linkage, pulled the plugs to inspect them, etc. etc. Finally, I got it to fire up and it ran like a champ. Just...took...forever...to get it to start.

The trick I found that helped to finally get it to start is that I squeezed the hand pump on the fuel line while I pulled the starting cord. When I'd do this, the carb was FLOODED. Meaning, gas was dripping out of about every orifice.


So, I'm not totally sure where to start and am a little gun shy to bring the boat back out again. Also, unfortunately, I don't have any means to fire up the motor at home, so I'm really looking for some strong pointers before I bring it out again (fortunately, it's only a 15 minute drive to the lake).

I'll replace the spark plugs, since I haven't done that yet, but they looked like they were in good shape.


Any ideas? Thoughts? Things to check? Parts to replace? Common culprits? (Both my wife and my vehicles are outfitted with aftermarket performance carburetors, so I know my way around a carb very well. Just never messed with one on a boat before. So any advice is appreciated.)


Thanks everyone. I'd like to get this motor trustworthy.

Are you 100 % sure this is a 4 stroke motor ???------Are you mixing gas and oil at 50:1 on it ????????????????

I thought it was listed as a 4-stroke when I was referencing the serial number, but I maybe I got it mixed up? I'm not able to check it right now. Either way, I used 4-stroke motor oil in it (50:1 ratio), so if its a 2-stroke, is that going to hurt it??

Did some quick reading and from what I read, 4-stroke outboard oil won't damage it, but will foul everything right up.
I'm assuming I fouled up the spark plugs with the 4-stroke oil in the gas?

You may have a glob of oil sitting in the carb bowl. Clean the plugs and get rid of the fuel/oil mix...dump it into the car tank...it won't kill it but will dilute it if you fill the tank. Run some Seafoam or Merc. power tune thru the engine so it cleans out the crud. Use merc. TWC3 oil in the gas...stay w/it.

Thanks for the advice on the cleaners. I'll be sure to do that.
I'll pull the carb back off and clean it out. Simple little thing so it shouldn't take too long. Plus, I'll just replace the plugs since I don't know how old they are. Is a place like Autozone going to have them?

Is the 4-in-1 oil a lost cause? Or can that be used in a regular car engine too?
I don't know anyone who'd need it otherwise.

Is the 4-in-1 oil a lost cause?

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Is it automotive grade? Read the spec...SG**** to see if it meets auto specs.

I'll take a look when I get home. Thanks again.

Just a quick update, I got the motor all cleaned out and it runs fine again. Have some seafoam in the gas, which is helping clean everything out. Runs really strong.

The problem I'm having now (and also realizing why it was taking forever to get started) is a fuel delivery issue.
It was taking forever to get started before because there simply was no gas. I'd prime the hand pump and then try to start it and just pull, and pull, and pull..... Nothing.
Finally realized that if I KEPT priming the hand pump until there was gas pretty much flooding out of the carb, it'd fire to life. (Hand pump is new BTW).
Last time we took it out, it would run strong and then, without warning, go from full throttle to 0 in about two seconds. I'd have to work to get it started again. Finally found that if one of us kept pumping the hand pump while the other steered, we could keep it running strong back to the dock.

So, since then, I've replaced the fuel line, which was old and hard (but not cracked) and wasn't sealing against fittings due to how hard it was. I've also replaced the rotted gas tank gasket.
I have yet to go out and test it to see how it does.

However, the last thing I'm not sure I understand is the adjustment on the gas cap. There's a finger grip adjustment that I can tighten or loosen. Does anyone know what this is for? I figure it's some type of vent, but I don't know how to adjust it properly.
Any insight would be great.
Thanks

I figure it's some type of vent

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Yes, it is...leave it open fully CCW when running the engine. Youi need to make sure the carb is delivering fuel as designed...sounds like it needs a good cleaning and blow out w/compressed air.

Thanks for the info on idle and checking for vac leaks.

Well, had the boat out this weekend for 3 days straight (loaded it up with camping gear and headed out across the lake, lots of fun). After a few trips, I started to learn the "sweet spot" with the choke and throttle to get it to fire up after only 2 - 3 pulls of the pullstring. Once I got it down, I knew that if it wasn't trying to start, more pulling wasn't going to help. I just had to adjust one or the other. Really saved my hands!

However, the bad news is that it doesn't seem that any amount of tuning is going to get it to idle right. I can get the RPMs down, but if I get them too low, the whole motor will kick and buck, and then die. I have to keep them up rather high to keep it running. However, once running, it never stalled or quit, so I have the fuel issue taken care of. I did about eight 2 - 3 mile trips (15 or so minutes straight at a time) ferrying things around and it ran the whole trip each time. The only oddity I noticed is the pitch of the engine kept changing like it'd drop a few 100 RPMs now and then. (GPS clocked me at 11mph and I could see slight speed drops when the pitch would change of around 0.1 - 0.2mph.)

I looked the motor over while it was running and discovered that water was slowly dripping from the top spark plug hole. My guess is a cracked block? I can't think of much else. It'd explain why it's having running problems at lower RPMs.

If this is the case, is the motor pretty much on its last legs? Or is this something that can be fixed on a small engine? Or, is something else maybe causing it?

Water cover gasket needs to be replaced.---------six small bolts and a $3.00 gasket.

You might want to sand that cover before putting it back on. (I've found that they warp and will not seal properly, even with a new gasket.) I use 100 sandpaper taped to a window pane for a flat surface. Keep the part flat, move is softly, and rotate it now and then as you slide it back and forth.

Jeff

Water cover gasket, huh? Well, that sounds a lot easier!
Thanks for the heads up on that, and for the plate possibly being warped. Good to know.

Where on the motor is this generally located?

You say it is dripping water around the sparkplug hole !----So that is where this gasket is.

Be very careful removing those bolts. They like to snap off.

Jeff