Ok, I am stumped. Mercury 115hp (tower of power) stumbles/boggs at WOT

[merkurfan]

Engine came to me as a non-runner. Cleaned carbs (removed them, soaked them, blew passages out) and checked compression. #3 was a little low at 90 PSI but I just double checked it today and it's at 115 and all are with in 10% of each other. It was probably operator error with the gauge or the rings freed up from sitting.

I set the mix screws at 1.5 and once running turned them in to what would be 1.25

This engine idles fine, starts right up, pulls decent but once I pass about 3/4 throttle it bogs and sputters. It can't push the boat much past 10 MPH.

I have cleaned the cap contacts, replaced the plugs (with the proper ngk) tested spark and get a nice blue spark on all 6 plugs.

I think it's getting to much fuel. At WOT with the sputtering and what not the bulb is hard and giving it more fuel (spray or choke) makes it worse.

it'll idle all day long and cruise at 1/2 throttle or less as long as you want.

I should mention I have been through the carbs twice. It's a fixed mixture on the high side.

 

[oldplumber61]

Re: Ok, I am stumped. Mercury 115hp (tower of power) stumbles/boggs at WOT

i have a 1972 1150-115 hp. takes off good, at 2/3 throttle it goes flat and dies. took to my mechanic and explained . first thing he said is exhaust splitter is broke. he took the power head off and it broke and fell over the exhaust hole and stopped it up. i havent found one yet.didnt say your model but could be tour problem.

 

[Texasmark]

Re: Ok, I am stumped. Mercury 115hp (tower of power) stumbles/boggs at WOT

i have a 1972 1150-115 hp. takes off good, at 2/3 throttle it goes flat and dies. took to my mechanic and explained . first thing he said is exhaust splitter is broke. he took the power head off and it broke and fell over the exhaust hole and stopped it up. i havent found one yet.didnt say your model but could be tour problem.

Sounds like something like this, out of the ordinary. If his split maybe yours did too. You touched everything else I would have recommended. I know removing the powerhead is a PIA but you need to do something else to fix the problem.

Thinking about the engine as an air pump, which it is, it makes perfect sense to me since you are having too rich symptoms. You can suck it in on the intake stroke, but can't blow it all out on the power stroke and it's volume (rpm) related.

Mark.

 

[BatDaddy1887]

Re: Ok, I am stumped. Mercury 115hp (tower of power) stumbles/boggs at WOT

Did you rebuild the fuel pump? Check the fuel filter at engine? Open fuel tank and check for debris on intake hose? Water separator problem? Perhaps high-speed windings in stator are bad.

 

[emckelvy]

Re: Ok, I am stumped. Mercury 115hp (tower of power) stumbles/boggs at WOT

Only the early 1150 and 1350 had an exhaust divider. 1972 was the transition year, so if your motor is newer than '72, it has a different exhaust plate without any type of removable divider. If you suspect a blockage, instead of pulling the powerhead you could drop the lower unit and look up the exhaust tube for any big hunks of carbon in the way.

A distributor model won't have high-speed/low-speed stator windings, that type of stator is used in distributorless (ADI) ignitions. Point well taken on the fuel pump, if there's a pinhole in the pump diaphragm you'd get fuel sucked into the engine, causing a rich condition.

Last thought, if you're at altitude, the motor may be jetted too rich. Merc specified smaller jets for high-altitude operation. If you're at sea-level, this of course shouldn't be an issue.

Although, since this motor's past history is unknown, it might not be a bad idea to check the main jet size. Maybe some P.O. decided they could make it run faster by installing larger jets!!! :facepalm:

It could happen!!!!

BTW on that 58478A 1 exhaust divider, from what I understand it was an effort to improve low-end-torque, I wouldn't worry too much about replacing it if you can't find one. Without it, you may notice a slight decrease in low-end, but your top-end will be a bit better.

You might check with Sea-Way Marine in Seattle, they have all sorts of oddball N.O.S. parts squirreled-away. Sea-Way Marine-your source for Marine Parts - Johnson Outboards, Evinrude Outboards, Chrysler Outboards, Mercury Outboards, OMC & Merc Cruiser Sterndrives

OK, just checked eBay and there was a new one for over $100, but also another one for $52.42 shipped. Better grab that one before it's gone, last time Merc priced this NLA part it was $94.35!!!

Divider Assembly 58478A1 Mercury Mercruiser Motor Engine Boat | eBay

HTH.........ed

 

[Chris1956]

Re: Ok, I am stumped. Mercury 115hp (tower of power) stumbles/boggs at WOT

Check the spark plug wires for arcing to ground. Check the spark plugs for water intrusion. What kind of boat is it on? What pitch prop. 10MPH is real slow for 1/2 throttle.

 

[oldplumber61]

Re: Ok, I am stumped. Mercury 115hp (tower of power) stumbles/boggs at WOT

i hope you get yours going merkurfan. i like the way the old 6's run. owned several even one old direct drive.thanks emckurfan for the link to the splitter,got it ordered.

 

[wired247]

Re: Ok, I am stumped. Mercury 115hp (tower of power) stumbles/boggs at WOT

Why did you turn the idle screws in? You dont use the idle screws to smooth the idle out. There is no transition circuit on those 2 circuit carbs. The idle has to be fat to move from idle to the mains and the float level has to be spot on. Otherwise it never transitions to the main circuit and you go 10 MPH. Smooth the idle out with timing once you have a good idle to main transition.

 

[mr 88]

Re: Ok, I am stumped. Mercury 115hp (tower of power) stumbles/boggs at WOT

^ x2 Those idle screws probably should be out 2 + turns to get the beast off the idle circuit.Try it at 2 and if it is better but not full on then open each one up about 1/8 of a turn,starting with the top,then check,then middle and check etc. I wonder if the OP is even reading this as there has been no response from him.

 

[merkurfan]

Re: Ok, I am stumped. Mercury 115hp (tower of power) stumbles/boggs at WOT

sorry, I just got a digest e-mail tonight about it. I figured iboats would have sent one earlier..

To date, the boat still does not run right. I pulled it for the season but I guess I can always dump it in till the lake freezes.

Why did I turn the idle in. It helped. It is not a lean problem. it's rich. adding choke makes it worse. Fuel tank is clean and works fine on other boats. This seems to be in this engine. The engine is on a 19ft Cobia 180. it's a big fat boat. However, the motor came off a 1973 Larson Shark. it was a tad smaller, but just as heavy.

I'm guessing I have to do what I hate. Go back in to the carbs.

One other thing that came to me.. The cobia was missing 95% of the orginal engine. I had the wiring harness and the transom mount basically. The SN on the mount came back to around 1982 vintage. The harness in the boat was for that engine I assume. The motor I installed is obviously much older, I think it's a 72 or 73 as the Larson was a 73. Even though it cranks and starts, could there be something in the newer harness or maybe the tach in the boat causing a problem? the tach does not work but that does not mean it's not causing a problem.

 

[mr 88]

Re: Ok, I am stumped. Mercury 115hp (tower of power) stumbles/boggs at WOT

You say you turned the idle screws and it made it helped. Did it help your slow/idle speed or did it help your acceleration? In most cases if not all,the idle screws are more in the 2-2 1/2 out mode. Choking will make it worse,your starving it of air and that has nothing to do with the acceleration transition of the carbs. I would start with the idle screws before taking another step. No the wiring harness etc is not the cause of your issue.

 

[Chris1956]

Re: Ok, I am stumped. Mercury 115hp (tower of power) stumbles/boggs at WOT

What pitch prop do you have? Is there arcing from the plug wires to teh block?

 

[wired247]

Re: Ok, I am stumped. Mercury 115hp (tower of power) stumbles/boggs at WOT

Do what Mr.88 says. The choke on that motor is a choke. Its not an enricher. That pushing the choke thing to see if it helps with your lean bog doesnt work on carbs with actual chokes. Open your idle screws and raise your idle timing.

 

[merkurfan]

Re: Ok, I am stumped. Mercury 115hp (tower of power) stumbles/boggs at WOT

will do. I am not sure if I'll get it in the water this weekend.

With the idle screws where they are it idles smooth, richer and it tends to act rich. sputters a smokes.

Fuel is fresh non corn premium.

 

[wired247]

Re: Ok, I am stumped. Mercury 115hp (tower of power) stumbles/boggs at WOT

Your problem is THE single most common inline mercury problem. People adjust the idle screws like you do on a car and they fall flat off idle and don't transition to the main circuit. The idle screws and orifices act as the transition circuit to the main jets. Open them up 2 1/2 turns then advance the idle timing until you get 700-800 RPM in gear in the water. If you can transition start turning them in until you cant then bring them out 1/4 turn or so.

 

[oldplumber61]

Re: Ok, I am stumped. Mercury 115hp (tower of power) stumbles/boggs at WOT

havent saw a post if your's is running, or your model but got the exhaust splitter in mine and it runs like a scaulded dog. good luck.