95 Merc 115 - low prms - wont plane

Its a long story heres the shot version:<br />Have an 84 Bayliner 20 hardtop. Removed the old volvo, installed bracket and used 115. Went on my maiden voyage and it wont plane/low rpms.<br />Details:<br />1. New stator<br />2. Starts quick/runs smooth<br />3. Bulb stays hard<br />4.While trying to get going, I noticed the rpms jumped up suddenly for a second. this happened a few times.<br />5. I think i have a 17 0r 19 pitch prop<br />6. I did notice that i think the bottom carb (1 of 4) leaks some gas out of the bottom. The other do not?<br />What Im gonna do:<br />1. idle her, remove plug wires one at a time to see difference.<br />2. Clean the hull bottom. (does have some barnacles left over from when it sat for a few days with no bottom paint after the old volvo blew..)<br /><br />Heres what I KNOW:<br />1. Yes the boat is underpowered to begin with and cpould be the culprit. i FIGUED THAT THE VOLVO WAS ONLY RATED AT 110 HP AND IT PLANED ooops so why shouldnt this set up?<br />2. Yes the barnacles could be it.<br />3. Yes, the prop might be wrong.<br /><br />What I WANT to be the problem:<br /><br />1. When i was young i have a merc 40. It wouldnt plane. I took out the needle valve and it had black crud. I cleaned it and it planed. Easy and free fix<br /><br /><br />Any other ideas or suggestions without rehashing what i know could be the issue? I reall hope its a clean-the- carbs problem or a faulty pack i.e. running on 3 cylinders. I am eager to hear any ideas because Im at the end of my rope with this project!<br /><br />thanks

Re: 95 Merc 115 - low prms - wont plane

oh yea, excellent compression

Re: 95 Merc 115 - low prms - wont plane

oh yea, i dont have a tach yet so i cant tell you what the numbers were. probably in the 2000's

Re: 95 Merc 115 - low prms - wont plane

The fuel out of the carb is definitaly a problem while running. Either needle and seats are leaking or a float is stuck, or it's so saturated with fuel that it lost boyancy.<br /><br />Start with your carb rebuilds, then move to your fuel lins (air in on the vacuum side, and restrictions in the tank), then move to your fuel pumps and rebuild them.<br /><br />All are cheap parts and easy to do yourself.

Re: 95 Merc 115 - low prms - wont plane

I had a customer with that problem. It turned out to be one of the accelerator pump injectors. It had a bit of metal preventing it from closing. Gas leaked into the crankcase and out the bottom carb. I thought it was the carb at first, but rebuilding did no good and it was clean anyhow. That was one in a thousand. Other far more likely causes are a torn diaphragm in the fuel pump or the carb needs a rebuild. Do all 4 of them if you do any of them. I think you'll find a 19 pitch prop a bit too steep. I'll bet you end up with a 15.

Re: 95 Merc 115 - low prms - wont plane

thanks guys.<br />im using a new portable tank with new lines/bulb so i can rule out that problem. Im going to pull that bottom carb and mess with it a bit.<br /><br />so do you guys agree that if this boat planed out with a factory volvo aq 125 i/o rated at about 110 HP, it should also plane out with a 115 outboard as long as there is only one passenger, little fuel and a dry bilge?

Re: 95 Merc 115 - low prms - wont plane

ok new and disturbing informaton.....<br /><br />this is a 4 cylinder. lets call the carb/coil on top #1 and they go down to the bottom #4.<br /><br />I started pulling off coil wires:<br />1.clearly affected....almost stalled<br />2.clearly affected<br />3.no effect<br />4. no effect<br /><br />if fact i even pulled 3 and 4 out at the same time and no difference. this baby is running on 2 cylinders!<br />wierd part: When i took the wires off 3 and 4, there WAS a spark jumping on both. I swapped out plugs and wire positions with 1 and 2 to rule them out and they are fine.<br /><br />so now, i seem to have spark going to 3 and 4. i also think that it might be a good spark, unless you cant tell by eye (i.e. it may look like a strong spark but it isnt?)<br /><br />so then i started thinking about the possibility of no fuel getting to carbs 3 and 4. that would be bad. well, i pulled the fuel line hose that connect 2 and 3 and gas pissed out. OK, so 2 is letting 3 get gas. sounds logical. I pulled the fuel lines bw 3 and 4 and 3 pissed out some fuel. OK i guess. <br /><br />Then I started looking at the needle screws. I am by no means a carb man but what i did notice i that on carbs 1 and 2 i found a typical needle screw, you know brass colored with a spring. they were both about 1.5 to 2 turns from bottom. Well, when I look at 3 and 4, instead of the screws with springs there are brass regular type screws and they were just sealed tight. I pulled them out, no spring, no needle just about 1/8 of and inch of regular threads and thats it.<br /><br />anybody have a clue ghere? is this normal? why would somebody put them in? to rip me off?<br /><br />PLEASE help

Re: 95 Merc 115 - low prms - wont plane

i just checked the book. apparantly, the low speed adjustment screws are not equipped on the bottom 2 carbs. that must be that.<br /><br />you know what im gonna do? swap the top 2 coils with the bottom 2 coils. if the top 2 cylinders dont fire and the bottom do, then them coils are bad. what do u guys think?

Re: 95 Merc 115 - low prms - wont plane

I saw a movie on checking spark the other day. Some of the experts can correct me, but I believe good spark should be able to jump 3/8in.<br /><br />You put a bolt in your plug cap and see how far you can make the spark jump.<br /><br />Easy way to check if you're getting fuel is run the engine with plug wire 3 and 4 disconnected. Run only for 30 secondes or so. Switch off and remove the plugs. They should be wet.<br /><br />Also, with the engine running and all plug wires connected, spray sum premix into the dead cylinders' carbs. Listen if they fire up.<br /><br />A note: Be careful, if your engine is a 2 stroke and cylinder 3 and 4 arn't getting fuel, it means they're also not being lubricated.

Re: 95 Merc 115 - low prms - wont plane

Ok you don't have a problem with 3 & 4, I'm not sure what year it started but the 115 hp went to a 2 + 2 version. During low speed up to approx 1800 RPM it only uses 2 cylinders and after that speed it adds the other 2. My understanding is that 2 carbs only have high speed circuits (they have minimal fuel feed to the cyl for lube only, but not enough to generate any power). Sound's like you are not getting the RPM's up enough for the other 2 to join in and you may not given the size of the boat you are trying to push with only 2 cylinders!

Re: 95 Merc 115 - low prms - wont plane

mercfan, good ideas ill try em.<br /><br />bob, i have thought about the 2/2 thing, but my understanding is that this is not a 2/2 motor. could be wrong. If anyone out there knows for sure what years they started please chime in. this motor is a 94 or a 95.<br />i guess it is strange that the bottom 2 carbs are lacking low speed adjustments though. i could just rev her up with rabbit ears and pull the plug wires off one at a time and see what happens under those circumstances.<br /><br />i am quite certain that it was revving well above 1800rpm when i was out on the test run. more like 2800<br /><br />in the meantime if anyone has any ideas as to what might prevent the other 2 from firing on a 2/2 id like to hear it. <br /><br />thanks again guys

Re: 95 Merc 115 - low prms - wont plane

Esan,<br /><br />I'm hoping an expert will comment, but 94-95 is pretty new and could very well be a 2+2. <br /><br />Wha's the serial number? Will help the guys here alot!

Re: 95 Merc 115 - low prms - wont plane

serial # is g238660<br />115 hp<br /><br />The latest:<br /><br />I tried running the motor for 30 seconds without the 2 bottom plug wires hooed up. when i took them out they wee wet. they werent SOAKED, just a little moist. they were bone dry when i put em in. just to make sure, i did the same for cyl 2 (one that i know works) and it also came out wet but not soaked. MAYBE a little wetter than the bottom 2 but im starting to split hairs now.<br /><br />so does that sound like fuel/oil getting to the bottom cylinders? i sure dont want to fry em while troubleshooting.<br /><br />NEXT:<br /><br />i shot some fuel into the 2 "dead" cylinders while idling. it didnt sound like there was any reaction.<br /><br />THEN<br />I swapped coils top for bottom. There was no change=coils are probably working.<br /><br />THEN i started looking at the control linkage. It seemed like the maximum rpm stop was way overadjusted. I revved it in the driveway almost full blast and it seemed like it wasnt that much. i took a dozen turns off the screw and the throttle moves and extra 3/8 inch now and i can tell that i can overrevv it now. <br />\<br />Thats GOT TO BE at least part of the problem<br /><br />it still doesnt explain why the bottom 2 dont seem to make any difference if they r hooked up or not UNLESS thisd is a 2+2.<br /><br />so up there is my serial. can somebody please give me some info on the 2+2 system...when do the other 2 kick in, what type of switch or whatver does that i.e. what tells the other 2 to come on? do i have a 2+2 i believe its a 94 115<br /><br /><br />thanks a million guys

Re: 95 Merc 115 - low prms - wont plane

well i scraped the barnicles off the hull and went for a quick test ride. it ALMOST got on plane. if i just had a bit more i would have broke it.<br /><br />I am pretty sure one or more of the cylinders are not firing 100%. i can tell when i was doing 5 knots that it seemed to kick in here and there a bit stronger.i dunno....<br /><br />so any info especially for 2+2 theory would be nice

Re: 95 Merc 115 - low prms - wont plane

No info from me on the 2+2.<br /><br />Hopefully someone else can help?<br /><br />Is this motor a 2+2?

Re: 95 Merc 115 - low prms - wont plane

Well, just sitting here and watching the ball bouncing back and forth, I'm gonna throw in my 2c.<br /><br />You said 2+2 needs 1800 rpm's and on your setup with your 19" pitch it won't let you get there apparently. Since all these things are different between 1-2 and 3-4 I'm inclined to agree on the 2+2. Now, if you had a 15, like Willy B suggested, your engine should be able to jump past 1800 on the hole shot, kicking in the bottom two and power you out. <br /><br />The 115 has a 2.07:1 gearbox so for that boat, with my experience in that area, you are way over propped. <br /><br />Just ran a quick calc on your setup, assuming you are heavy so I used 20% slip at WOT which I think is reasonable gives you Theoretical 37 mph at your 5250 WOT recommended rpm's and with the 20% slip you are still sitting at a realistic 30 mph. Which is not bad and almost 2x the speed it takes to plane.<br /><br />So my may, it may be a matter of the forest for the trees syndrome. Your engine may be just fine, you just won't let it get up and show you what it can do......but the leaking fuel you mentioned earlier needs to be corrected if you haven't already.<br /><br />On the test you ran when you said 3 and 4 were wet, you said that the engine allows some fuel to the unused cylinders so that must be what it is. It's not dry because apparently your 2+2 mechanism is controlling spark to 3 and 4 (seems like an easy way to do it) and since you are low in rpm't there isn't any spark to explode it.<br /><br />One last thing. I did a quick check on your setup with 1800 rpm max (where 3 and 4 should kick in) and my arithmetic says that at 1800 with your 19 with a 2:1 your 100% max speed is 16....just under planing speed......BUT WAIT. Factor in slip, and it's a different ball game. I used 40% slip under plane, which I can relate to some of my experiments and I think it is a valid number, says that the boat is only doing 10 mph. <br /><br />You can't get there from here.....PROP is definitely part of the problem.<br /><br />HTH,<br /><br />Mark

Re: 95 Merc 115 - low prms - wont plane

Forgot something.<br /><br />Have read on here (several folks in this Merc section) that they couldn't get up on plane till they changed their pitch (lower) and things worked just fine. Bet they had the 2+2 setup and had the same thing you have.<br /><br />I was confused about that initially (before knowing about 2+2) cause I was looking for a mechanism as to why the load was so bad that the engine wouldn't even attempt to overcome it. <br /><br />Normally the engine would push as hard as it could and you would just have a lot of prop slip (and wear and tear on the engine). I have towed logs before with the engine at WOT just to get the log moving (then throttled back), and never had an engine balk.....course never had a 2+2 either. <br /><br />But with what you said about 2+2, it's clear what the problem was and how the lower pitch allowed the engine to rev above the kick in point for 3 and 4 and away they went.<br /><br />Mark

Re: 95 Merc 115 - low prms - wont plane

ive been thinking about the pitch as well. i was also thinking a 15...<br />i went out today anyway ran her for an hour under easy conditions. i wish i had my gps, ill bet i was doing 9-12 mph.<br />i would still like to know what controls the other 2 cylinders to kick in though.<br /><br />well im going to blow a hundred and get a new 15 prop. stay tuned....

Re: 95 Merc 115 - low prms - wont plane

SUCCESS!<br /><br />THanks everyone.<br /><br />Well alls i can say is that i cant believe what a difference a prop/pitch change makes.....<br /><br />I bought a 15p mich match for 100 bucks and she came out of the water like butter<br /><br />I do indeed have the 2+2 and heres how it works: there is a plunger that contacts the throttle cam as you increase throttle. when it contacts, it diverts fuel from the bottom carbs that is restricted, and shoots it directly into the cylinders drilled off the side of the block. when you are trolling the plunger is not activated and a tiny fuel flow goes to the bottom carbs for lube<br /><br />OK so i have one new proplem:<br /> when i was up on plane, the rpms sort of went up and down with the waves. it sounded like when your on a sailboat in chop and the prop pops out for a half second. i know the prop is new so it cant be slipping. <br />could the gearcase be slipping? <br />it is also possible that the prop was just coming out of the water a bit but i hve to have my wife run it so that i can look it at.<br />unfortunately, the boat was pointing bow high too much, and yet the engine is in the most foward position. (the power t t is broke). If the prop was coming out of the water, that would be bad because if i fix the twim manually the lowering of the bow makes the stern rise and then the prop really might come out,<br /><br />either way, if i take a little off the gas you can hardly feel it so if that the best its going to get bow up thats what ill do- 15 mph<br /><br />maybe ill install trim tabs<br />so if the prop is well in water, what could be causing slippage?