1995 merc 115 bog at top end

[pinboy122]

Hi all.My 95 115 merc 115hp(4 cylinder 2+2)has a bog at the top end.It bogs around 4600rpm which is the last 3" of travel on the throttle/gear shift handle.If I back it down until it runs smooth I can trim it up and get about 5300 rpms and it runs smooth.I went through the carbs in the spring when I bought it,put in new plugs and re-built the fuel pump.Im not really sure which way to go next.Also the thing starts like crap.Im going to get the starter rebuilt because it barly spins the motor for the 1st few turns then it spins as it should but sometimes(doesnt matter if its warm or cold)it just wont start.I might have to try 4 or 5 times.Any thoughts??? thanks Al

 

[mercman2]

Re: 1995 merc 115 bog at top end

Well Al I have a 93 115 idle on 2 run on 4. The carbs are very tempermental when cold I have to make sure the engine is level or somewhere close to start and I usually have to give the choke a couple of bumps till she warms up but after that it starts fine. Sounds like yours is starving for fuel. Run it up to where it quits and bump the choke if it picks up then it's fuel related. Either primer bulb,fuel connector or just in need of a carb job (which would probably help with the hard start).But I would start with a compression test and a spark check.

 

[pinboy122]

Re: 1995 merc 115 bog at top end

Thanks mercman.I noticed the keep it level thing too.It also seems to do a little better if I prime the ball everytime.I'm a little worried about the starting problem because I plan to use the boat for night time walleye fishing well into winter.I like the push the choke during the bog idea.the compression was good with the lowest at about 135,the spark checks out good as well.

 

[Maxz695]

Re: 1995 merc 115 bog at top end

I,ve herd this before some time back I think it was an electrical issue but unless someone with more knowledge comes foward try what you feel is best

 

[mercman2]

Re: 1995 merc 115 bog at top end

I have owned my 115 for 11 years it rest on a 1750 Procraft ProFish which my fellow yankees call a walley boat. It has a bass boat bottom and runs in the low 50's with a custom prop.My friends here in the south call it the battleship. LOL They aren't laughing when I come to the scales. Check the choke thing first fuel issues are the easiest and cheapest thing to fix. I'm not discounting a switchbox or stator because they can act up at WOT. I had to replace the stator in mine but it wouldn't fire at all. Theses parts are expensive. Quite honestly I would trust this motor to get me to Mexico if there were gas stations on the way

 

[Dave1027]

Re: 1995 merc 115 bog at top end

Hi all.My 95 115 merc 115hp(4 cylinder 2+2)has a bog at the top end.It bogs around 4600rpm which is the last 3" of travel on the throttle/gear shift handle.If I back it down until it runs smooth I can trim it up and get about 5300 rpms and it runs smooth.I went through the carbs in the spring when I bought it,

This sounds like carburetor float level too low. Like one of the carbs is running out of gas. How did you set the floats? You better not run the motor like that. You could burn the cylinder.

Is the starter disengaging while trying to start? Lube the starter shaft so the pinion will fully engage.

 

[Jlawsen]

Re: 1995 merc 115 bog at top end

The one thing that concerns me is the way it's cranking. Do you mean the starter has a hard time at first then after a couple of try's it spins normal. The hard starting problem is the second thing. I've rebuilt a few 2+2's in my time and there's a number of things that can cause problems.

The first thing you want to do is a compression test, If you don't know how to do it, just ask. A fresh 115 will give you about 135lbs of compression after break-in. I've seen some that will give 140 too so if you have that don't be alarmed.

Before you do your test, warm the cylinders by removing the plugs, gounding the plug wires and then cranking it for a few seconds. Make note of any spray or mist comming out of the spark plug holes.

During the compression test, you should have all the plugs removed and the spark plug wires grounded. Cranking speed should be around 300 rpm using the starter.

 

[Maxz695]

Re: 1995 merc 115 bog at top end

I own an 86 Procraft 1750

 

[pinboy122]

Re: 1995 merc 115 bog at top end

Jlawsen,what I mean about the starter is that each time I turn the engine over it spins very slowly(like a real low battery)then zings pretty good.All connections are tight and clean.The + terminal on the battery side was a little crappy so I put a new terminal end on.The battery is ok,not the best but even after a full charge with the charger still connected the starter acts the same.I did 2 compression tests.One before purchase,and another when I was diagnosing a funny looking plug.When I got the boat home and put it in the water I was disappointed with the performance.I pulled plugs and the top plug was different than the rest,so I did another check and the compression was all near 135 give or take a couple pounds.What I found was the carb linkage rod wasnt connected to the top carb so I snapped it back on and went back on the water.Now,other than the high end bog and the starting issue the boat runs great.It comes out of the hole like a beast and runs nice and smooth.I can bypass the bog spot using the trim and run it up to 53-5400rpms.The boat tops at about 40 on gps.
DAVE1027...I didnt really pay a lot of attention to the float settings,I gave the carbs a basic tear down check and clean jets blow out passages ect.I really didnt see anything that made me think "gotcha!". Im beginning to think I might have to go back into the carbs and take some more time. Thanks everyone for the posts keep em coming!!!

 

[Dave1027]

Re: 1995 merc 115 bog at top end

Check all connections to the battery, solenoid and starter. If all that is good then it could be the brushes in the starter are going bad.

I can bypass the bog spot using the trim and run it up to 53-5400rpms.

That further reinforces my opinion it's float level. Why else would trim attitude matter?

 

[pinboy122]

Re: 1995 merc 115 bog at top end

I got the day off tomorrow so I think ill try to get back into the carbs and see whats up.Dave, im not disagreeing that its a float in fact I hope it is because thats an easy fix.When I trim it up while running, the engine attitude doesnt really come up that much,its getting the boat up out of the water reducing drag and strain on the engine.I dont know...Hopefully I find something wrong in there.While Im in there is there anything that I should watch for that could contribute to my hard starting problem?Any shared experience or ideas greatly appreciated thanks Al

 

[BatDaddy1887]

Re: 1995 merc 115 bog at top end

+1 for the brushes going bad. I rebuilt my starter a few years ago and all went well for me. I even made the special tool to help re-assemble it....I bought a plastic 4 inch putty knife and cut a one-inch section from the middle to the, and used that to hold the brushes in place while I slid the cover back on. Worked like a charm. Of course I got that idea from this wonderful forum!

 

[pinboy122]

Re: 1995 merc 115 bog at top end

UPDATE.....I finally got the time to get some work done on the boat.I had the starter rebuilt and the difference is night and day.It sometimes starts hard but Im not worried because it spins so nice,its just a matter of tinkering with the choke and throttle.Now to the high end bog.I put new kits in the carbs with new inlet needles.1 carb had a float that was about 1mm low,everything else looked good.The bog is still there.The boat is still totally usable and its easy enough to "work around" the bog but the fact remains that something is still wrong.Im open to all suggestions. thanks Al

 

[pinboy122]

Re: 1995 merc 115 bog at top end

little bump

 

[CharlieB]

Re: 1995 merc 115 bog at top end

Did you 'bump' the enrichener at the Bog, what if any effect happened?

What spark plugs are you using?

Inspect the piston domes thru the plug holes, what color?

Are the carbs synch'd, accel pump adjusted and timing all exactly as specified in the FACTORY service manual.

You may still be able to find a copy of the manual thru links in here

http://forums.iboats.com/showthread.php?t=309079&p=2072211#post2072211

 

[pinboy122]

Re: 1995 merc 115 bog at top end

Charlie,I did sync the carbs but couldn't check the timing because my timing gun hasn't found its way home from the last guy to borrow it.the enrichment button didn't seem to have any effect on the bog.I'm not home now so I don't know which plugs but they were speced from my seloc manual and we're the same # that was in it.

 

[CharlieB]

Re: 1995 merc 115 bog at top end

What I found was the carb linkage rod wasnt connected to the top carb so I snapped it back on and went back on the water.Now,other than the high end bog........ the boat runs great.It comes out of the hole like a beast and runs nice and smooth.I can bypass the bog spot using the trim and run it up to 53-5400rpms.The boat tops at about 40 on gps....................
................................bogs around 4600rpm which is the last 3" of travel on the throttle/gear shift handle.If I back it down until it runs smooth I can trim it up and get about 5300 rpms and it runs smooth...............................

I've cut and pasted clues from a couple of your posts.

It is normal for a motor to pull up just so far with the drive fully down as the water drag on the gearcase limits speed, adjusting the trim, raising the gearcase just that much more out of the water reduces drag and the motor then can accelerate to boat to top speed.

This may not be a 'bog' or even a problem with the motor. You may want to check the set up, the mounting height of the motor on the boat. With the trim set level check the alignment of the A/V plate immediately above the prop to see if it is even to one inch above a line drawn back from the bottom of the hull. If the boat has a 'pad', that flattened space at the bottom rear of the hull imagine a yardstick held against it sticking out towards the drive, the A/V plate should be at or an inch above that line, any lower and too much drive is dragging in the water.

Underway the motor can only accelerate the boat till drag equals HP at that RPM. The only way to increase speed is either add more power, a larger motor, or reduce drag, trim the motor a bit.

HP is a function of RPM, increasing to max power at max RPM. Even high HP V6's experience this and make trim adjustments during acceleration to WOT.

It's hard to tell from these posts how much experience you have or if you do still have a motor problem.

 

[pinboy122]

Re: 1995 merc 115 bog at top end

Im getting to my wits end with this thing.Im beginning to think "thats just the way it is".Ive checked everything I can think of.Over the weekend I checked the in tank fuel pick-up and screen-ok.Checked the wot timing and that was .5 degree off so I left it.I made a few runs as fast as I could and pulled the plugs.The top 3 were a nice even tan color but the bottom plug was a bit darker.I suspect my description of the dreaded "bog" may be confusing so I will try to simplify it. No matter where the trim or rpms are the engine will bog down when I get to about the last 3" of the throttle handle range.As far as the bog I guess it could be a misfire on 1 cylinder,I just dont know.Pushing the choke(enrichener)makes it worse.Im going to pull the carb cover off to check that the butterflies are not over opening.Im hoping someone who has had this trouble will see this post and save the day!Charlie,I will check the a/v plate but without looking at it I would guess the motor sits lower than what you are saying.

 

[CharlieB]

Re: 1995 merc 115 bog at top end

Swap the #4 coil and wire with any of the others, after your next outing check the plugs again to see if the darker plug followed that coil. It could be a weakness in that coil or plug wire under full load.

That or the #4 carb float is not exactly the same as the others.

 

[pinboy122]

Re: 1995 merc 115 bog at top end

I got a chance to take a quick look at the boat today and still didnt find anything to fix my problem.I pulled the air box off to check the butterflies and they all looked pretty good.I was hoping 1 of them was opening past horizontal but that wasnt the case.1 of them(top carb)was a little off so I adjusted it back in line with the others.None of them open completely horizontal they all stop just a little short.I checked the throttle cam,cable barrel,throttle stops and whatever else I could see to no avail.For whatever reason I just cant push the accelerator handle all the way down without loosing power.Its almost like a cables out of adjustment but everything checks out.Charlie,I checked the a/v plate and surprisingly enough its right on.I didnt change that #4 coil yet but I will before my next outing.I think Im just going to ride it out for the rest of the season which for me doesnt end untill the ice shuts me down.Thanks for all the tips and input and If anyone can think of anything Im all ears. Thanks AL