1977 Evinrude 115 Runs Rough At Idle

[Robert1967az]

I have a 1997 Evinrude 115HP that runs rough at idle and smokes a lot. It smells like it's running very rich. I rebuilt the carbs and set the floats level with the housing and re-installed. Starts better that it did but still rough and rich. Pulled the carbs off and adjusted the float up a little. Still rough and rich but better than before. I've ordered a float gauge from an online outfit that took a month to send me parts in the past, so I think it will be a while before I can set the float to exacting specifications. Checked the fuel pump to crankcase port and it is bone dry. There are no idle mixture adjustments on the carburators so what could be making it run so rich? Any suggestions?

 

[1946Zephyr]

Re: 1977 Evinrude 115 Runs Rough At Idle

I would do a compression test on all four. They should be as even as possible

 

[emdsapmgr]

Re: 1977 Evinrude 115 Runs Rough At Idle

A couple of different could be contributingto your problem. It is not unusual to have idle problems if there is any dried fuel or debris in the fuel passageways in the carb bodies. Carb overhauls are the way to insure all the passageways are clean. Your overhaul should include: removal of all jets (the high speed and the idle jets-total 4 per carb.) Inspect the jets for debris and shoot some aerosol carb cleaner through them. Take each carb body and shoot carb cleaner through a passageway on one carb- noting the resulting spray on the outlet of the passageway. Pick up the other carb body and spray the carb cleaner through the same passageway, noting the spary on the outlet of the passageway. You need to insure that all passages flow the same-esp check the flow through the idle passages, as they are pretty small: dried fuel/debris can settle there. Note the jet sizes, stamped on each jet, and compare it with the factory spec jets for your engine at the Bombardier parts website: epc.brp.com just to verify you have the correct jets. Some engines will smoke more if their rings are carboned up-you should run a can of Bombardier Engine Tuner through the powerhead and see if your starting and idling improves. An engine which is running cold will smoke more due to poor combustion. Verify that the vernatherm is functioning correctly, permitting the engine to heat up. If it is stuck open, the engine will run cold and you will have poor combustion and carbon can accumulate around the rings. If you tilt your engine for shallow water running (or for overnight storage,) it is not unusual for some fuel to leak out the front of the carbs into the airbox. This excess fuel will settle in the bottom of the airbox and will get recycled into the lower cylinder through the airbox drain hose. When that occurs, the engine will smoke for a brief period of time, till the excess fuel is burned off-a "normal" thing on these engines.

 

[Robert1967az]

Re: 1977 Evinrude 115 Runs Rough At Idle

Lots of good information, thanks.

I do have a compression problem, three cylinders are running right at 100-105psi and one is at 90psi; 120 on a wet test. I'm hoping, fingers crossed, it's a stuck ring and decarbonizer will loosten it up. I added seafoam to the gas and will get some decarbonizer spray. She's been very cold blooded ever since I got her and I think EMD may be right about the thermostats, I'll pull them and check them out. I get water spitting out of the two round ports at the back of the engine immediately at start up, shouldn't they not flow till the thermostats are open? Anybody have a preference of decarbonizer, any one stands above the rest? Sea Foam products (gas additive and Deep Creep) are easy to find and reaonably priced, but I once tested the gas additive by soaking a fouled spark plug in it for two days and it hardly touched the carbon. Maybe it works when combusted? I've seen some posts about Mystic Miracle oil? I can attest that a fouled spark plug will look like new if soaked long enough in brake fluid, but that doesn't help me any with a possible stuck ring.

My bad on the original post, the mortor is a 1977.

 

[1946Zephyr]

Re: 1977 Evinrude 115 Runs Rough At Idle

That's okay, the headline says 1977, so you're good.
My suspicions exactly, you have differences in your compression readings. This is a large contributor to the rough idle. I don't know if decarboning will do anything for it, but it's worth a shot.
Any motor that's been in use recently, should have the rings loosened up plenty good. If there is any sticking rings, it's likely because of piston scoring around the ring grooves. Decarbing an engine is what you need to do for an engine that has sat for years, but I usually do this, with a little extra heavy mix.
I can verify this, because I have a 53 year old 18hp in my shed right now, that was stuck when I got it, but now runs like a clock. I even found rusted out spark plugs when I got it home. A little WD-40 and running it, everything is flushed out and cleaned up. LOL Main thing is, the pistons are not scored and I have over 100 psi per hole.
The V-4 models were notorious for reed valve problems and scoring pistons, dating back to 1958. The old 50's and 75's had reed valves that were extremely fragile and were prone to failure. I think if you pulled the bypass covers off and looked through the ports, you can get a good visual of the pistons and see if there is any scoring. The intake side is where the particals typically enter and creat issues. The exhaust side is the side that gets hotter but the particals are already burned. It's been said that 50:1 is okay on these, but I think more like 32:1 is better on the V-4 units. This is because I see a lot of problems with uneven compression. The bigger motors like the V-4's and V-6's....V8's included, are more of a performance engine. I have a 25 that was designed to run on 100:1, but it was quickly discovered that "that don't work" Many motors like it were recalled and the owners got free rebuilds. My old 18 was designed to run on 24:1 and that is probably why it has held together for 53 years even after being stuck and water in the cylinders.

It's possible you may need an overhaul, but I would explore the free checks first.

Fouled plugs should be tossed and replaced with new ones.

Ignition systems should be kept in clean operating order

An engine that runs at high rpms more than low, should be a little rich on the oil mix. A typical fishing engine that usually spends it's time trolling is good at 50:1, but these big motors that pull a lot of wakes and skiers......well....I would richen it up a bit. A fouled plug is better than a scored piston.

 

[emdsapmgr]

Re: 1977 Evinrude 115 Runs Rough At Idle

The cyl with low compression may just need to be decarboned. I'd do that decarb procedure once or twice (does not hurt to do it a second time,) then see where your compression is. The Bombardier Engine Tuner is one product that does work well, esp considering their recommended application procedure. If you are concerned about the low compression on that one cyl, you can pull the intake bypass cover off just that one cyl (as was mentioned in a prior response) and have a look at the ringsets and piston skirt. Check for carbon around the rings or on the piston skirt, and for piston scuffing (aluminum transfer from the piston to the cast iron cyl walls.) Yes, you are correct-typically the water mist does not start to come out of the exhaust ports till the (vernatherm) thermostat opens up. If yours starts pumping a water mist immediately, your stat may well be stuck in the open position. Normally, after warmup the heads should be in the 145-150 degree range. You can easily test these temps with a laser temp gun. If you don't have one, you can probably rent one cheaply from the local auto parts store.

 

[Robert1967az]

Re: 1977 Evinrude 115 Runs Rough At Idle

Here's an update for you guys.

I ran a can of Engine Tuner through it and set the carb floats to exact spec. Lots of carbon came out but still running rough. I finally decided to tear it down and have a look inside. Two pistons had carbon fouled rings. There was no way chemical cleaning would have fixed it, I cant get to the ring buried under the carbon even with a screw driver.

So the rebuild is on! I found a machine shop that is owned by a guy that is a boating fanatic. He recommended Weisco forged pistons and I respect his knowledge. The pistons added about $100 to the rebuild kit but luckily I'm not strapped so I don't mind spending a little more. The motor is torn down to the block, cleaned, and sitting on the bench awaiting the rebuild kit.

I can't get the machine work done till the kit arrives because the macine shop matches the pistons to the cylinders individually.

I'm looking at $850 in parts and machine work but I'm learning a lot and having a lot of fun with this project.

Thanks for all your advice, I'm sure I'll need you guys again when I reassemble and install it. In the mean time I'll keep you posted.