1999 Mercury 135hp bogs down out of the hole

DollarShort · July 05, 2015, 07:26:08 PM

I bought a late 1990's SeaRay fish and ski boat about 3 years ago. I'm guessing on the year of the boat, but the tag on the motor says 1999. It's an oil injected 2-stroke. The boat has had very little use, but I believe it was stored outdoors for several seasons. Considering the outdoor abuse, it's a good boat, no major issues in the 3 years I've run it, but there is a nagging issue with the motor.

My problem is that the motor dies when I try to "goose" it onto the trailer. It also bogs down when I try to pull a water skier out of the water, and sometimes stalls right out when I pour the coal to it.

It's not a terrible problem, but it makes me think something is wrong, and it's embarrassing at the end of my Wednesday night bass league when everyone is waiting for me to get loaded. They all have such nice boats, and their big Mercs make me have motor-envy. Those big throaty OptiMax motors sound awesome, and I feel like a dufus when my motor pukes out.

I changed the plugs and the fuel filter this weekend, but no improvement. The motor looks like new under the hood. In fact, I'm pretty sure the plugs I changed were the originals. I've searched around the net and came up with plugs, fuel filter, and something about the ignition. I tried 2 out of 3, the third sounds expensive. I'm a good mechanic and have good luck with most motors, but this one is frustrating me.

One other small issue that may be related is every once in awhile the motor seems to lose its prime. What I mean is it'll die out on acceleration and stall and then not want to restart. I have to prime it to restart, and the primer bulb is soft. This issue is intermittent.

Anyone have experience with Mercurys or know where I might look? I have a pretty good set of tools, and I'm always looking for an excuse to buy another one.

Princeton_Man · July 05, 2015, 07:51:54 PM

Sounds like your primer bulb or fuel line may have a small air leak. Could explain a lot of things.

DollarShort · July 05, 2015, 08:10:33 PM

It runs well when above an idle, sometimes it idles well, sometimes I have to choke it on and off while idling.

I'll check the lines, thank you.

bjcamp · July 05, 2015, 09:00:27 PM

Sounds to me like your experiancing a problem related to the Ethenol gas and it my have your carbs, gummed up or the fuel lines compromised.
Another thing you might check for is that insects [ mud daubbers ]may have an air intake blocked and your not getting an air flow to your gas tank .

DocIrv · July 05, 2015, 10:58:11 PM

Same problem in my merc 225 efi 1997 the exhaust holes inside the middle unit were plugged up with carbon and once it was removed it ran great.

DollarShort · July 06, 2015, 06:59:41 AM

I'm not clear what holes you're referring to Doc.

Thank you everyone for input

Mike Cork · July 06, 2015, 01:23:08 PM

The ports Doc is talking about are basically you exhaust that run exhaust from the motor to the prop.

But, a mud dobber has been the culprit of frustration with many boaters. If they block your fuel tank vent line (very easy for them to do, especially on a boat stored outside) then you get a fuel cavitation when your motor sucks hard. I've seen all your problems caused by this several times.

Also a check valve in your primer bulb that is ineffective will cause all these issues. Both are cheap and easy to clear (vent) or replace. I'd start there.

Next would be making sure your fuel is free of water. If the previous owner let the tank sit empty with no additives, you could be running as much as 20% water. I've seen this happen a bunch to because of bad gas, no additives, and condensation from years of sitting. If the vent was plugged by a mud dobber the condensation could have been bad.

DollarShort · July 06, 2015, 05:32:42 PM

1. Fuel line air leak - I'm assuming the only test is to replace it and hope it helps. Replace all the lines from the tank to all carbs? Wouldn't there be a small fuel leak or evidence of fuel leaking at this small hole?
2. Tank vent - I'll be darned if I can find a vent for the fuel tank. I assume it's in the cap, but I am unable to blow air through, either way. When I put a small pool of lacquer thinner in the little recesses in the cap, none of it appears to leak through. That makes me think those little recesses are just to put in the screws from the opposite side. Pictures attached, I hope

3. Exhaust ports Doc mentioned - do I need to remove the lower unit to inspect these?

Thank you for bearing with me. I'm learning something with every comment you post.

DollarShort · July 06, 2015, 05:38:21 PM

4. Water in the fuel tank - I believe he ran additive because there was some in the storage bin in the boat, but I don't know for sure. I assume the only way to be sure is drain the tank completely and start fresh. Not exactly sure how to accomplish that, but it is low on fuel currently, so now may be the time to figure it out.
5. Primer bulb - I've changed those on my old boat. That seems too simple. I tend to always try the complicated stuff first and fail, then take stuff to a professional, and once again relive the truth of "Stuff's easier when you know what you're doing."

I have sprayed the carbs with carb cleaner, but nothing more than that. I'm not sure I am capable of tuning 6 carbs if I mess things up. I manage with single carbs, usually by adjusting while running, but not sure I dare mess with 6 at a time.

bjcamp · July 06, 2015, 06:10:31 PM

On my old Nitro , the gas tank "air vent " is not on the filler cap , but rather on the opposit side of the boat and had a screw on cap that vented.-- look for evidence of mud duabbers there.

Mike Cork · July 06, 2015, 06:13:28 PM

Typically the vent will be a separate tube going to the tank. It will be much smaller than the full tube. I've see where it's simply vented to the bilge area and not to the outside of the boat, common in boats that have a vented bilge.

My boat has the vent tube ran back to the gas fill. When I look into the gas fill valve I can see a small opening for venting. If I look at my gas tank I can see this tube. So I have two tubes that run from my tank to my fill cap.

In previous years my boat manufacture had a separate hole in the boat for venting, however this was bad business if the one way (out) system failed, you could get water in your tank.

Another thought because it sat. Fuel pump diaphragms can get holes in them from drying out. It could be a cause of all your issues as well. Since your not afraid of maintanence, it's a relatively easy change that's not expensive. Unfortunately to check it you have to tear into it and will need a gasket that comes with the part.... I think they are about twenty bux, but don't quote me... With outboards prices vary greatly on year models.

DollarShort · July 06, 2015, 07:51:27 PM

Ok, here's the latest.
I was sharing with my wife about everyone's comments and ideas and how excited I was to get wrenching. Her response with a long face was, "How about I try to work a little extra and you can take it to someone who knows what they're doing." It seems she doesn't share my mechanical confidence.
Disappointedly, I went back to the garage and gave the engine another thorough going over, with no tools other than a flashlight.
I did find a second line going from the tank to the cap, but I'm pretty sure that's the overflow that shuts off the pump at the gas station. I haven't found any other opening to the atmosphere that might vent the tank.
So I started looking very closely at all of the fuel lines, the ones I could see without and parts removed. Everything looked good, felt good. I noticed there was a small solenoid-looking thing on one side of the motor with lines running to 2 of the carbs.
I read somewhere online in another forum that there is sometimes an "acceleration pump" on some outboards. This pump apparently gives the motor a little extra boost of fuel on initial acceleration and can sometimes cause issues similar to mine. I started following wires and got really confused. Then I starting looking more closely at the lines that went to the 2 carbs mentioned earlier. Attached are a few pictures of what I found. Is this one of those pumps? Could this be my problem?

Princeton_Man · July 07, 2015, 10:42:16 AM

I'm not a Merc man. Only owned one (did work on it a lot). I did some pic/diagram searches and that looks like what they call an enrichner valve. From what I read it performs like an electric choke.

DollarShort · July 09, 2015, 11:25:35 AM

I think you're correct, that was a choking mechanism. The motor did seem to run a little better last night, but still puked out loading on the trailer

Mike Cork · July 10, 2015, 08:36:58 AM

Just out of curiosity, what prop are you running? Too high pitch prop can cause the trailering issue. Doesn't really explain the other issues.

Princeton_Man · July 10, 2015, 11:24:05 AM

I'm wondering if your fuel system has a water separator/filter either on the motor or in the battery/bilge area. If you do and it's near the full/replace point, any time the bow comes up it may be introducing some water into the fuel. $:-\$

DollarShort · July 10, 2015, 09:10:35 PM

My prop is stainless, 21p stamped into it. That mean something?

Mike Cork · July 11, 2015, 07:50:14 AM

That means it's a 21 pitch prop and it should be correct for that motor. Back to thinking

DollarShort · July 11, 2015, 01:03:10 PM

I went out this morning for a few hours. The motor ran and idled well, however it lost prime and the bulb went soft twice when I was taking off.

hughesjasonk · July 11, 2015, 01:21:15 PM

I would chech your pick up tube

merc1997 · July 11, 2015, 02:23:44 PM

i have read through all the thoughts on your problem. you have not mentioned whether or not you run fine once you manage to get up on plane??? if so, you have a good chance and having your reed valves leaking. a 1999 engine is now 16 years old, and most likely the reeds have not ever been touched. since the originals are metal, they fatigue and start to leak. very similar to having a valve on your car engine leaking.

seems as though you have checked just about everything else.

bo

DollarShort · July 11, 2015, 06:00:05 PM

The engine does run well once on plane. I have not yet changed all of the fuel lines and the primer bulb. Reeds sound like wrenching, I'll have to do that while my wife is sleeping

DollarShort · July 11, 2015, 06:03:33 PM

The only times I notice any issues is when trying to load on the trailer (will almost never rev up to push onto the trailer, just bogs out,) occasionally when trying to take off even if slowly advancing the throttle, and when trying to get a water skier up. Basically acceleration from an idle, whether quickly or gradually.

Terry D · August 14, 2022, 03:27:51 PM

Hi Dollarshort.
Did you ever solve this problem? I'm having the same problem. Thankyou!! Terry D.

BassmanRudy · August 15, 2022, 12:43:15 AM

Adding this as a thought. I had some issues with my 2009 90hp motor cutting off while at full speed. Checked fuel filter, fuel lines, bulb, all were good. Ended up changing the really small line going from the tank to the 90 degree nipple(also took the top part off and wire brushed off all the junk on it) and she ran fine afterwards.

May not be exactly your problem but worth checking?