1986 Mercury 115 "Tower of Power" Reed Valve Problem

[txarmydude]

I ran the boat last weekend and it ran terrible. It had absolutely no hole shot. I had to slowly give it throttle until I had a running start before I could give it enough throttle to plane. If I gave it too much, it would die. I ran it like that for a little while, and the problem got progressively worse through the day. The motor eventually would not go over 3200 RPMs and was surging right before that.

The boat just had a new stator put in, new carb kits, and a water pump. I took it back to the mechanic and he said that it either had bad reed valves, or the "lower unit timing" was off (I had never heard that one before). However, he said they had the lower unit apart, and everything was looking ok. They just couldn't get the lower unit timing adjusted. He said that lower unit issue is rarely a problem.

He told me that if the reeds are bad, I probably shouldn't put that much money into a motor that old. According to him, the powerhead has to come off and the engine basically has to be rebuilt. Roughly 2 grand is what I'm looking at.

Any opinions/comments are appreciated....

 

[boatman192]

Re: 1986 Mercury 115 "Tower of Power" Reed Valve Problem

never heard of the lower unit being in time either.

 

[metriccrescentwrench]

Re: 1986 Mercury 115 "Tower of Power" Reed Valve Problem

"Lower unit timing" - now I've heard everything :facepalm: . I wouldn't give that "mechanic" another penny.

Who installed the stator, carb kits, water pump, etc.? What was it doing before that, and did it ever run ok after that work was done?

It's probably time to get yourself a factory service manual and start asking a bunch of questions. There's enough collective knowledge on iboats to solve any problem.

 

[txarmydude]

Re: 1986 Mercury 115 "Tower of Power" Reed Valve Problem

"Lower unit timing" - now I've heard everything :facepalm: . I wouldn't give that "mechanic" another penny.

Who installed the stator, carb kits, water pump, etc.? What was it doing before that, and did it ever run ok after that work was done?

It's probably time to get yourself a factory service manual and start asking a bunch of questions. There's enough collective knowledge on iboats to solve any problem.

He didn't call it exactly "lower unit timing". When I talk to him again I will let you know exactly. He fixed the stator because it had poor spark. All three carbs were rebuilt as well. He put the water pump in at my request, just as a precaution. The floats had fuel inside them, which he showed me. The motor started doing this after I got it back the first time. He looked at it again and realized that the 3rd carb had fuel inside the float as well. He ran it in his tank and it ran great, and didn't charge me for the work. I took it out this time and had the same issue.

Every time I took him the boat he has had it back within 1 day. This time, he has taken 3 days so far and has not been able to isolate the problem. He said that he will know for sure after he has the lower unit put back together completely. But again, he said he has not ever had an issue with the lower units before, so the reeds are probably the culprit.

The boat has good compression and spark, right now.

I have no reason to believe that this guy is dishonest. He comes highly recommended by numerous friends. The one who WAS dishonest was the guy who sold me this boat.

 

[metriccrescentwrench]

Re: 1986 Mercury 115 "Tower of Power" Reed Valve Problem

The one who WAS dishonest was the guy who sold me this boat.

Ouch. Unfortunately I know all too well about that (at least guys selling supposedly good engines).

IF by chance your engine needs reeds they're not all that difficult to replace.

 

[txarmydude]

Re: 1986 Mercury 115 "Tower of Power" Reed Valve Problem

Ouch. Unfortunately I know all too well about that (at least guys selling supposedly good engines).

IF by chance your engine needs reeds they're not all that difficult to replace.

I thought you had to remove the powerhead and disassemble the crankcase to replace the reeds on this type of motor.

 

[aussieflash]

Re: 1986 Mercury 115 "Tower of Power" Reed Valve Problem

He probably means "Pickup Timing" as a possible culprit.
I know my V6 reeds are accessible by removing carbs and reed block..Not sure about the tower though.

 

[gwukena]

Re: 1986 Mercury 115 "Tower of Power" Reed Valve Problem

Doubt it's a reed problem. Usually on the towers a sign of bad reeds is they won't idle down low enough(hard to idle below 1000 rpm) without dying, How's your idle rpm in neutral and in gear? And yes to change the reeds, you have to split the crankcase.

Almost sounds like your timing is off and/or dropping spark from cylinders. Make sure trigger is advancing when you throttle up and not hanging. If idle stabilizer still connected, disconnect and throw it away.

Your going to have to figure out is this a fuel issue or ignition. Has fuel pump been rebuilt, does pumping primer bulb when throttling up help?

You may have to hook an inductive timing light to each cyl while acting up to see if they are getting fire. Then dva test the crap out of it using the cdi troubleshooting guide Switch boxes, stators (which you already replaced), rectifiers and triggers are known issues on these motors, good news is coils rarely fail. And don't forget about plug wires (know someone who replaced all ignition components and in the end it was bad plug wires) You need to test and retest until you figure out the problem, electrical parts add up quickly on these motors.

Lots of times these things run fine in tanks and on muffs, it's when you put a load on them that the ignition system can't keep up.

Problem nowadays is there aren't too many techs familiar with the towers and end up guessing at problems.

HTH
Gary

 

[txarmydude]

Re: 1986 Mercury 115 "Tower of Power" Reed Valve Problem

Usually on the towers a sign of bad reeds is they won't idle down low enough(hard to idle below 1000 rpm) without dying, How's your idle rpm in neutral and in gear?

The engine does not idle well. I usually have to give it a little in neutral to get it to run. At low RPMs it usually dies.

 

[gwukena]

Re: 1986 Mercury 115 "Tower of Power" Reed Valve Problem

The engine does not idle well. I usually have to give it a little in neutral to get it to run. At low RPMs it usually dies.

At what rpm on tach?

 

[txarmydude]

Re: 1986 Mercury 115 "Tower of Power" Reed Valve Problem

I really did not check, to be honest. I asked the mechanic if there was a possibility that the fuel pump was bad, since it was surging on the water. My Mercury manual says that the most common cause of surging is a failing fuel pump. However, the mechanic says that there is "no chance" that the fuel pump is bad.

If I get the boat back un-repaired, I will probably replace the fuel pump anyway.

 

[narvlebenoit]

Re: 1986 Mercury 115 "Tower of Power" Reed Valve Problem

the fuel pump is a cheap rebuild 20 bucks do it yourself.Ihave 90 hp had sourt of the same thing happen changed coils stator switchsboxes rectorfire finally got tired brought it to a friend thats a outboard mach. he changed the trigger runs great now he said triggers hardly go bad but some do.

 

[txarmydude]

Re: 1986 Mercury 115 "Tower of Power" Reed Valve Problem

UPDATE - The mechanic confirmed that there was a problem with the lower unit. It was intermittently locking up both at idle and in gear. He replaced the lower unit with a new one and the boat ran great all weekend. He only charged me 500 + tax installed because he said he doesn't like it when customers have to come back for the same problem. The motor's g2g now; I just need a new prop to get in the proper RPM band. Thanks for all advise!!!

 

[gwukena]

Re: 1986 Mercury 115 "Tower of Power" Reed Valve Problem

UPDATE - The mechanic confirmed that there was a problem with the lower unit. It was intermittently locking up both at idle and in gear. He replaced the lower unit with a new one and the boat ran great all weekend. He only charged me 500 + tax installed because he said he doesn't like it when customers have to come back for the same problem. The motor's g2g now; I just need a new prop to get in the proper RPM band. Thanks for all advise!!!

I call BS, did you get your old lower unit back?

 

[Chris1956]

Re: 1986 Mercury 115 "Tower of Power" Reed Valve Problem

An intermittant gearcase? I never heard of that one. The sometimes slip, and you get that "Banging Sensation".

That doesn't fit your symptoms at all.

 

[txarmydude]

Re: 1986 Mercury 115 "Tower of Power" Reed Valve Problem

He showed me the old lower unit (which had a large chunk that had been taken out of the bottom where I banged it when I forgot to put the motor up at the boat ramp). The boat runs great now, though.

The only other issue I had with it is that now the speedo doesn't work. Is there a pickup tube on the lower unit? My last boat was a stern drive that had to have a separate pitot tube that wasn't connected to the outdrive. This boat has no such device. I assume it is in the lower unit, right? The water was really muddy and chunky because of all the rain...

 

[Chris1956]

Re: 1986 Mercury 115 "Tower of Power" Reed Valve Problem

Some of the lower units have the built in Pitot tube, some do not. You should see the entry hole on the leading edge of the gearcase. If not, a separate one always works.