Mercury 115hp hardstart

[smike26]

I just bought my first boat and have already learned alot from this site. I have a 1978 Mercury 115hp inline six(on a 77 Glastron) and haven't even brought it to the lake yet. I was told by the previous owner that it is very hard to start when cold. He sprayed starting fluid into carbs but I have since learned this is bad due to lack of lubricant. What's the best way? I also want to use a second battery for accessories, is there a way to charge two batteries at once.

 

[waynebo]

Re: Mercury 115hp hardstart

smike assuming the choke work the first thing i would do is a thorough decarb,it sounds like it might have stuck rings and a good decarb might take care of it.As far as charging to batts at one time just run them positive to positive and negative to negative and they will charge together as long as both batts are good.waynebo

 

[Hooty]

Re: Mercury 115hp hardstart

Instead of starting fluid use a squirt bottle with premix and squirt this into the carbs. If you gotta start it like this, I'd check the bulb to be sure it's pumping up hard and check the chokes to be sure they're closing the butterflys. If those seem o-k, you may be looking at a carburetor rebuild.<br /><br />c/6Hooty

 

[rons boat]

Re: Mercury 115hp hardstart

Hoot is right, one of the difference in the modern Mercury carbrurated engines in starting is due to the change from the old choke butterfly to the electic primer which squirts premix directly into the intake manifold. It makes a big difference in my Mercs as I have one each. With a conventional choke you have to run the starter to suck premix into the intake and with the primer you squirt before you engage the starter. On my 115 I do choke a little with the starter engaged and let off for a few seconds for the fuel to vaporize. It seems to help.

 

[Gold Bear]

Re: Mercury 115hp hardstart

smike26 <br /><br />I didn't see this post before I replied to your "request for advice" post. I am not surprised to see that you are having cold start problems with this engine. Believe me you are not alone.<br /><br />First, make sure the choke plates are working. Not only should they operate smoothly, they should fit snugly against the carb opening. If there is a lot of slack, tighten the pivot bolt down until the choke plate still operates smoothly, but the plate is held down snugly as possible over the carb opening. With my 115 I found that the tag end of the choke solenoid cable would often hang up on the choke linkage. A bit of "adjusting" took care of that problem.<br /><br />If you find that your engine is still hard to start after optimizing the choke, you can carefully spray some pre-mix fuel into each carb. It helps if you will tilt the engine all the way down, so the fuel will flow into the carbs (this seems to help a bit even if you are not using the squirt bottle).<br /><br />After getting tired of pulling the cowl (the first time of the day) I installed a primer system on my engine. It consist of a 1 gallon fuel tank, a 1/4 size fuel hose and squeeze bulb(you can buy a bulb at WalMart), three spray nozzles and a couple of 1/4" tees to route the hose. I installed a brass fitting with a screen as a pick-up tube, tie wrapped the 1/4" hose alongside the throttle cable and fit the spray nozzles into the carb opening screens arranged so the choke plate wouldn't hit them. Now, first thing in the morning I prime the regular fuel hose, squeeze the "primer" bulb a couple of times and she starts like a 2003 model!<br /><br />Seriously, now she starts so well that I do not even use the "warm up" lever any more.<br /><br />The parts for this simple primer system cost me about $10.00. If you do something like this be sure to do good quality work and remember just how dangerous gasoline can be.<br /><br />Good Luck,<br /><br />Gold Bear

 

[Hooty]

Re: Mercury 115hp hardstart

Golden Bear,<br />Now that's good, sound, Southern engineerin'!<br /><br />Congratz & c/6<br /><br />Hooty

 

[rons boat]

Re: Mercury 115hp hardstart

One other bit of advice. Use one good battery and keep connections tight. Never switch batteries with the engine running. The diodes in the bridge rectifier are easily damaged because they don,t have enough margin in what is known in Peak Inverse Voltage. The rectifier is a simple diode bridge like you can buy at a lot of electronic stores, but was engineered at a time when PIV values were less than a hundred volts or so. You can now buy 25 Amp bridges with PIV of 300 or higher volts, but are not in the fimilar package that mercury or replacement vendors sell for replacement. If your handy with a soldering iron, you can make a replacement bridge out of the higher rated units bought from an electronics store and the new bridge will take a lot more abuse. One loose connection or a hot switch of a battery will(with engine running) fry the old design bridges. Yes you can get a two battery feed, but I don 't recommend it for the reason discussed unless you change out the bridge with one of a higher PIV.

 

[smike26]

Re: Mercury 115hp hardstart

That primer idea is great, I'll start on it this weekend. Where did you mount the tank?

 

[Gold Bear]

Re: Mercury 115hp hardstart

smike26<br /><br />I have a 16' bass-boat. Under the aft deck is a 12 gallon size aluminum fuel tank, and there is a battery box mounted near by. The one gallon "primer" tank fits snugly in between the two. It is easy to pull that tank out to fill it with gas. I only mix about 1/2 gallon at a time, that way the "primer" fuel doesn't get to old. Also, if I feel that fuel is getting old, it is not a big deal to dump it out and mix a fresh batch.<br /><br />I was just lucky about the size of the primer tank and the space between the main gas tank and the battery. <br /><br />If it is not practical for you to install a separate "primer" tank, you could simply install a "tee" fitting in the fuel line before the primer bulb of your existing fuel tank. I choose not to do that because I felt like that arrangement would be another thing to "act up" on the primary fuel system. <br /><br />Just put some thought into your arrangement, and I'm sure you can install this simple "primer" system.<br /><br />Good Luck,<br /><br />Gold Bear