'81 Merc inline 6 115hp, bogs on accell

[olemerc115]

Hi, I searched this on google and was sent to this forum, I ran a search and found that my bog on accell, seems fairly common, I just bought the boat 3 days ago and it has a hydrofoil and a 17p prop, now I know why so it will help this ole merc get on plane because of the bog on accell, when it gets planed off it runs fine, no sputtering at high speed, but I did see a thread on here about someone removing the vent jets in the carbs to fix the bog, I would like to know where the vent jets are so I can remove them or how to bypass them the way it said with a needle bearing, I seen all this info on a search earlier but the link was dead from the other forum, scream and fly, I have only had it on the water one time, so any help would be appreciated, thanks again

 

[jimmbo]

Re: '81 Merc inline 6 115hp, bogs on accell

see below

 

[jimmbo]

Re: '81 Merc inline 6 115hp, bogs on accell

Disabling the "back drag" feature of the carb will not cure the bog on accelleration you are experiencing. It will prevent the engine from running too lean at part throttle. It was fine in 81 but todays gasoline has been altered chemically to be leaner.
Syncronization between timing advance and carb opening is very important on this engine, so are float settings, and idle mixture adjustment.
Drillling the prop helps a lot too by unloading the engine as it's coming off idle.

 

[olemerc115]

Re: '81 Merc inline 6 115hp, bogs on accell

thanks for the reply, I need to get a manual for this engine where can I find such a manual, and where would be a good place to get parts for this motor, thanks again

 

[olemerc115]

Re: '81 Merc inline 6 115hp, bogs on accell

well I checked compression on all cylinders and they are all good they range from 95 to 110, I havent tried it out on the water again but I did spray carb cleaner onto the outside and inside the carbs with it running and shut off, I checked the spark good and blue strong at idle on the muffs, I am sure this thing is going to bog again, I ran the gas out of it letting the engine run with the fuel line off, someone told me that is what needs to be done every time you run a 2 stroke outboard so the carbs will not get gummed up, my question is what does it mean to have a dropped cylinder, how will I know, do I have one, I thought that if the compression was good the base engine was fine and the bog concern is fuel or ignition related, I inderstand that under load either the ignition is failing on a cylinder or that the carbs are just not working right, I have a manual on the way, seems like someone should know how to fix these old bogging 115 mercs, looks like we all have the same problem, please help

 

[olemerc115]

Re: '81 Merc inline 6 115hp, bogs on accell

I looked for spark plugs on this website but couldnt find them for my 81 Merc 115 inline 6, couls someone please help me with a link or something, thanks again

 

[Chris1956]

Re: '81 Merc inline 6 115hp, bogs on accell

If the compression is good and no water is getting into the cylinders, usually the motor can be made to run real well, with a good trouble-fix and tuneup.

On that motor, the compression is good. Now put a timing light on each spark plug wire and make sure all six get spark. Now inspect the plugs. They should all be about the same color. If one or more look brand new, you could have water in the cylinder which "steam cleans" the plugs. If not, the carbs need to be rebuilt, or the idle mixture needs to be adjusted. Open the top carb idle mixture screw 1/8 turn, and see if the bogging is better. Repeat with the mid carb and finally the bottom carb. Repeat if necessary until you get a reasonable idle and smooth acceleration.

If you cannot achieve this, you need to tear the carbs down, clean 'em up and put in new gaskets and inlet needles and seats. Then adjust the idle mixture properly.

BTW- The spark plugs for that motor are likely available at any automotive parts store.

 

[olemerc115]

Re: '81 Merc inline 6 115hp, bogs on accell

thanks for the replies, I have checked the plugs, they are not steam cleaned they look ok, I will do the timing light check, thanks for the carb notes I will do that too, I dont know exactly what to turn but my manual is on the way, thanks again

 

[olemerc115]

Re: '81 Merc inline 6 115hp, bogs on accell

finally got to take the boat out again, this time it did not bog and ran great planed off normal, all I did was check my compression, good, used same old plugs, cleaned my carbs on the outside and sprayed some into them while engine was running on the muffs and turned the idle mixture screws on all 3 carbs 1/2 turn out to richen them, I also changed my prop from a 17P to a 19P because I was having some spun prop issues, plus it was turning way to many rpms and I wasnt going anywhere, I hope this post helps you guys out there, but I just want to say thanks to all the replies and it would have took me a lot longer to diag this concern on my own, hopefully the boat will continue to run ok for me, oh yeah I run the engine with the fuel line off until it cuts off everytime now, I am putting everything down that I changed or did different to help other people with this problem, of course It could have been a number of things but this helped my concern this time, anyway thanks again

 

[j_martin]

Re: '81 Merc inline 6 115hp, bogs on accell

finally got to take the boat out again, this time it did not bog and ran great planed off normal, all I did was check my compression, good, used same old plugs, cleaned my carbs on the outside and sprayed some into them while engine was running on the muffs and turned the idle mixture screws on all 3 carbs 1/2 turn out to richen them, I also changed my prop from a 17P to a 19P because I was having some spun prop issues, plus it was turning way to many rpms and I wasnt going anywhere, I hope this post helps you guys out there, but I just want to say thanks to all the replies and it would have took me a lot longer to diag this concern on my own, hopefully the boat will continue to run ok for me, oh yeah I run the engine with the fuel line off until it cuts off everytime now, I am putting everything down that I changed or did different to help other people with this problem, of course It could have been a number of things but this helped my concern this time, anyway thanks again

Upping the idle mix a bit is what did it.

John

 

[olemerc115]

Re: '81 Merc inline 6 115hp, bogs on accell

yeah I think that was it also, I was going to go the prescribed 1/8 turn but I figured what the hay just go 1/2 for good measure, it seems to rev hard on the bottom when planing off the way it should real pleased, I am going out again this afternoon if it doesnt rain too hard to try again, I lowered my motor on the jackplate, I couldnt trim it up hardly any without it coming out of the water, I lowered it today hopefully I lowered it enough so I can trim this baby out to drop the rpms and gain a little more speed, anyway thanks again

 

[olemerc115]

Re: '81 Merc inline 6 115hp, bogs on accell

took the boat out agin, it bogged really bad, just like before then will eventually plane off and run fine, then will bog almost everytime, then it will get better the more I run it, seems like it may be loading up not sure, I brought it home, disabled the back drag vacuum lines pulled all three of them off, vacuum capped all three carbs, idle mix screws at 21/2 all three, it bogged worse than ever, I revved the engine it eventually planed off, pumping the bulb seems to make it worse, because I backed off the throttle , put in nuetral and it stalled out and acted like it was flooded on the long crank, when started ran rough, until I revved it boggged a long time then finally planed off ran great, I pulled the cover off on the lake turned the screw out made it worse turned them in the same, I put them at 1 1/2 stock settings it idled better but 1/4 to 1/2 throttle seemed to be ok but when you go to WOT before plane off will bog hard and stall out, so I turned then to 1 3/4 same bog, eventually turned them all to approx 2 1/4 and it seemed to accelrate good until I tried to WOT trying to plane off, If I gradually tip into the throttle it powers up and planes off fine, I took it home and put my 17P prop back on it gonna try again soon, it had a 19P on it, wish me luck, this merc is really getting on my nerves, stupid bog is driving me crazy

 

[olemerc115]

Re: '81 Merc inline 6 115hp, bogs on accell

well heres another water test update, still bogs this thing seems like it is getting worse, I believe my engine is running rich because I can rev the engine then put into gear acts better, at takeoff if I go straight to WOT it bogs hard and takes forever to take off, but if I go 1/4 to 1/2 throttle it seems to power up better, also when it is bogging hard I get someone to pump the primer bulb the more they pump the slower I go, then it will stall out and hard to restart like it is flooding, I have turned the idle mix screws to 1 3/4 out my idle is better and wot it bogs hard, I disabled my back drag feature and to me it is worse now which makes sense because it is not leaning it out and midrange like it should to power up and take off, I am going to put the vacuum lines back on, leave the idle mix screws at 1 3/4 and try it again, I also put my 17p back on it instead of the 19p to make sure I wasnt overpropping this engine, I tried 93octane did not help went back to 87 octane at 50:1 mix, also I read thatmy enricher solenoid could be bad and riching upmy carbs, I know it works when I press the keyin because it seems to fire off better if I pu**** ina few times on cold starts, but if I use it to much on cold startsit seems to flood, how can I disconnectthe enricher solenoid to see, if it helps,I apperciate any help and thanks again

 

[Chris1956]

Re: '81 Merc inline 6 115hp, bogs on accell

OK - It sounds like you are about to blow a gasket. Let's take this one step at a time.

First check your fuel pump diaghram to make sure it is not leaking raw fuel into the crankcase.

Next set all idle mixture screws to 1.5 turns out form lightly seated. Now put the boat into the water start and warm up the motor in gear. Ok now adjust the idle screws in and out until the motor is running the fastest and smoothest. The idle mixture will likely be set too lean at this time, but the carbs are synched. Now try to accelerate. the motor will likely bog down. Open the top carb idle mixture screw 1/8 turn and try top accelerate again. Repeat with the mid carb, in that order. then open the lower carb idle mixture screw 1/8 turn and try to accelerate again. The top carb always runs a bit leaner than the mid carb, which runs a bit leaner than the bottom carb. Therefore the top carb idle mixture screw may need to be the most opened. You are done when it accelerated smoothly and idles decently.

 

[olemerc115]

Re: '81 Merc inline 6 115hp, bogs on accell

grat advise because Ihavebeen putting all scews the same turns out never thoughtthey would bedifferent, so the top car the leanest themiddle carb a little lean and the bottom carb will the the richest of the three, just making sure I get all this, also can ipullmy fuel pump apart to check the gaskets or will it tear the gasket whenI take it apart, but to me it it bogging because of a too rich condition, the more I turn the screws out thw worse she runs, also the more I pumpothebulbwhen bogging the worse she runs

 

[olemerc115]

Re: '81 Merc inline 6 115hp, bogs on accell

another water test update took theboat out yesterday, the motor neverbogged once ran perfect and planed off normal, lotsof throttle response, the onlything I changed was I put the vacuum lines back on all three carbs and left the idle mix screw at 1 3/4 out each, it idles fine when warm and has great throttle response the only thingis I have to pump the primer bulb to firm when cold starts and she runs great, this whole time I thought my 115 was running lean ansstarvingfor fuel was the exact opposite, it was way rich, I richen the screws too much pumped the primer bulb too much and choked it too much to start cold, the removal of the vacuum lines really richen my 1115 where it would barely run, I put them on and she ran fine sounded real nice, finally think I havethis puppy down, so it is possible anyone out there having this problem they areprobably creating a bog by throwing waytoo much fuel to the engine, I should havenoticed this because with the cover off no filter it ran better, rev up to clear engine it ran better way too rich, leaneris always faster,but I dont want to melt any pistons so a little rich is ok, just so you have decent throttle response, thanks again for all the replies and help, I take my boats out alot so I will keep everyone posted on this ole 115, I know these 115s arepicky so wish my luck, thanks again

 

[olemerc115]

Re: '81 Merc inline 6 115hp, bogs on accell

another water test update, bad news it bogged again, ran like crap, then would do ok, this little bog gremlin in really bugging me to the point that I might just sell the boat and forget it, I am at my witsend with this come and go problem, I was told by a proffesional local boat tech that the compression needed to be at 125 for all 6 to keep a good tune on these inline 6 because of the low torque they produce off idle to plane the boat off under load, I have around 100 and 1 cyl about 95 or so if I rember right, I may have this problem, I need more help guys I am stumped, I put into the wtaer she started fine idled great took off great planed off ran smoothto the honey hole fished for abou an hour then went to restart her hard start, pumped the bulb until firm, still hard start like maybe I pumped too much and flooded the engine, she started off then tried to take off started the bogging deal again would not plane off went to wot, then she would stall out, I pulled the cover turned the idle mix screws in 1/8 turn in to lean out a little, she atrted and bogged trimmed the engine upa little kept it at 1/4 throttle ran fine, tried the holeshot a couple times did ok, then she bogged again, this time I shot some premix into the top carb, she smoked hard and bogged down stalled out this thing has to be running rich at bog, the more throttle you give it the more it bogs, any help this thing comes and goes without me changing a thi0ng

 

[Chris1956]

Re: '81 Merc inline 6 115hp, bogs on accell

As long as the compression numbers are close to each other, the motor is tunable. There was never any optimum compression specs, and your compression gauge may vary in reading.


Stop messing with the mixture adjustment, as you likely have other issues. Did you check the fuel pump gasket for leaks? If not, this is the time. Also, check for spark on all six after it is warmed up and bogging.

 

[olemerc115]

Re: '81 Merc inline 6 115hp, bogs on accell

yeah I believe the idle screws are ok, how do I check the fuel pumkp gasket, do I just take apart and look at it, also how do I check for spark while it is bogging, on the lake, any helpplease thanks again

 

[Chris1956]

Re: '81 Merc inline 6 115hp, bogs on accell

If you can pull off the pulse hoses from the fuel pump, and pump the primer. if any fuel drips out you have a bad diaghram. or beter yet spend the $4 and rebuild it.

when it starts bogging, was it after any significant idling or slow speed operation? Put a timing light on the lower cylinders and see if you are getting spark. I believe your dual switchboxes generate spark to cylinders 135 and 246 respectively. maybe one is heat sensitive.