Logo
FULL SITE MENU

Mercury 1992 115 hp Inline 6 WOT Problem

J

jeff1967

New member
I have only had this boat for about 6 months. Not exactly sure of the year of the motor, but my boat is a 1992 Dynatrac 170, with a Mercury 115 Inline 6 "Tower of Power". Assuming this is the engine that came with the boat originally. Will verify the year if needed. My problem is the boat will not accelerate at WOT. Went to the lake yesterday for the first time this year. Boat was stored under cover during the winter. Took about 30 minutes to get the boat running, but it sounded and ran fine. Went a few miles down the lake, and the boat ran fine. Shut the boat off to do a little fishing, and when I started the boat back up to head back to the dock, the boat would not "hit" WOT. It would bog down, sputter and try to choke out. Had to idle back to the dock. When I finally got back and shut the motor off, tried to crank it. It would idle, but would die when I put it into gear. Another problem, (since I have owned the boat),is the boat doesn't start the way it should when cold. Would take five to ten minute to start it the first time. After it starts, hit the key and fires right up. Does anyone have a clue as to what is wrong, and how I need to check it. Plan to check compression. I am pretty mechanically inclined, but have no experience with boat engines. Thanks
 
Re: Mercury 115 Inline 6 WOT Problem

Well . it can not be a 92 as the last inline 6 was made in 88 I believe.-----------------Start with a compression test.---------------Check that you have spark at each cylinder that will jump a gap of 7/16" or more.---------------------You did install a new impeller when you bought it I hope.-----You did run the carburetors dry when you parked it I hope !!!-------------How does it run when you manually pump fuel into with the ball on the hose ????-------------------The starters are easily damaged with too much / too long cranking. Verify that choke or enricher is actually working / clicking.----------------Excellent motors if they are looked after and maintained.
 
Re: Mercury 115 Inline 6 WOT Problem

-Going to do a compression and spark test in the next couple of days.
-By impeller, I assume you are talking about the water pump impeller, which I did replace.
-Did not run the carbs dry. Didn't know you needed too.
-Did not try to manually pump fuel with the ball yet.
-I have been worried about damaging the starter by prolonged cranking. When I took it out for the first time, it seemed like it took to long to start. This was the first hint that something wasn't right. After it started, I could cut it off and it would crank back instantly, and ran very strong.
-The choke is working.
-It ran very well yesterday in the beginning, but after a couple of hours when I started back up, the motor would idle but would not open up. Had to idle back to the dock. When I got to the dock and tried to restart it to load the boat, it would die instantly when I put it in gear.
-Thanks for the reply. Will post again when I have more info.
 
Re: Mercury 115 Inline 6 WOT Problem

Maybe it is as simple as water in the fuel---------------------Inspection and trouble shooting is the way to go.
 
Re: Mercury 115 Inline 6 WOT Problem

Do you have a fuel filter installed? And it's not last years gas, is it? Even with stablizer, winter is too long for the gas to sit.
 
Re: Mercury 115 Inline 6 WOT Problem

The boat had about 1/4 tank of gas with stabilizer in it, the morning of the "incident" I put fresh gas in also. Have not noticed a fuel filter. Will get one and install and drain fuel tank. Will probably be this weekend, when I do all of this. Thanks for the replies, At least I know where to start. Will keep you updated.
 
Re: Mercury 115 Inline 6 WOT Problem

There will be a factory fuel filter near one of the fuel pumps. I never ran my inlines dry, when you tilt them the carbs dump enough fuel for it not to matter. Never had problems from leaving it like that for months either, inline carbs have relatively tiny fuel bowls. Inlines typically run surface gap plugs, so any nice white/blue spark is fine. Obviously can't be gapped.
Inlines MUST use the highest grade fuels you can find and like to be underpropped a little and spun up to around 6k at full speed/throttle.
It sounds to me like you definitely have a fuel restriction or excess fuel.
As for your cold starting, prime the fuel line a LOT, like till fuel runs out of the carbs, stand on the bulb if need be and choke the engine fully until it runs, not till it catches. You may need to "blip" the choke on and off to keep it running the first 20-30 seconds if really cold but it should settle down nicely after that. Quite often inlines will catch on a couple of cylinders first if the carbs have been dry a while, then the fuel pumps fill the rest of the carbs and all is fine for the day.
 
Re: Mercury 115 Inline 6 WOT Problem

I did the compression and spark tests today. Compression on 5 cylinders were 130 and 125 on the other. Spark test on all cylinders jumped a gap of at least 7/16". Going to drain the fuel and clean the carbs next. Is there a way to test the fuel pump?
 
Re: Mercury 115 Inline 6 WOT Problem

The bulb in the hose is nothing but a manual pump.----------------If the motor runs properly if you keep squeezing it then you have a pump problem.------I have found the disc on the checkvalves in the pump to be sticky , perhaps due to our modern fuels.
 
Re: Mercury 115 Inline 6 WOT Problem

I doubt it's fuel pumps suddenly sticking valves. Inlines do like to perforate diaphragms though.
 
Last edited:
Re: Mercury 115 Inline 6 WOT Problem

The poor cold starting on those is often caused by the choke plates not closing tight enough. Bending or shimming fixes that. The bog off idle is usually caused by the carbs opening way before the advance comes in. Adjust the throttle stop screws and/ or the cam that opens the carbs to allow the mag to come almost to full advance before the carbs START to open.

It looks complicated, but if you study it a while you'll figure it out.

Jeff
 
Re: Mercury 115 Inline 6 WOT Problem

Hard starting on the inline 6 can be caused by many issues.---------Worn pistons / rings --------worn labarynth seals internally----------reed valve problems ---------Slow cranking starter etc etc.---------------One cure is a switch to an electric primer system.-----------Later Mercs had it or a system from a Johnson / Evinrude is easy to fit.
 
Re: Mercury 115 Inline 6 WOT Problem

Finally made it back. I have the carbs off and getting ready to rebuild and clean. My question is the serial number is 5922011, can someone tell me what year it is?
 
Re: Mercury 115 Inline 6 WOT Problem

Here's an update. Drained the fuel tank and water separator. No water in either. Cleaned carbs and blew out with compressed air. Did not see any trash in any carb. What I have discovered is the rubber on the end of all three of the needles is swelled, not letting the needle come down, and not letting gas get to the carbs. I will be replacing these this afternoon. A mechanic told me that ethanol based gas will cause this. After checking the place where I purchase gas, I found out their gas does contain ethanol. Will have to make sure in the future not to do this. Will update when I get the carbs back on. Anyone need 10 gallons of weed trimmer gas? LOL
 
Re: Mercury 115 Inline 6 WOT Problem

Put the carbs back on with new hoses, needles and seats, annd fresh non ethanol gas. After 6 or 7 revolutions, boat crank and run like it should. Believe this was a problem since I owned the boat. Have not had on the water yet due to the high water after the recent storms we have had. Will inform after the boat can be put under load.
 
You may need to "blip" the choke on and off to keep it running the first 20-30 seconds if really cold but it should settle down nicely after that. Quite often inlines will catch on a couple of cylinders first if the carbs have been dry a while, then the fuel pumps fill the rest of the carbs and all is fine for the day.








Buy WoW GoldBuy World of Warcraft GoldRS Gold
 
The only thing that is not working properly now, is the tach. Could someone post a wiring schematic or tell me which wire to check? Have visually checked what I can see. Thanks
 
Back
Top