1979 Evinrude 15hp poor idle

I just picked up an old 1979 15hp that was used as a kicker for a long time. This motor runs great wide open, but I need to adjust the idle speed so high the nylon adjuster nearly falls out of the knob. <br /><br />This motor does idle, but misses a lot. I put new spark plugs in it - gapped at .030". It will idle slow enough to troll, but again, it misses a lot.<br /><br />According to the design, I should be able to adjust it down in a postion that would depict a lot slower engine rpm than I can reach. The idle speed setting it is at now, would suggest a very HIGH idle speed.<br /><br />I believe the idle jets are plugged. Any ideas out there? How to clean them? Use fine piano wire, carb cleaner, air nozzle?

Re: 1979 Evinrude 15hp poor idle

Hi there & welcome. <br /><br />I've got the same motor a year or two newer. Slow trolls for hours without a miss, so there's definately something wrong with yours.<br /><br />I haven't done a carb clean on mine (no need), but here is a great article about these motors. The author (no me), does post on this board.<br /><br />If it were me, I'd try carb cleaner & compressed air before wire. I've heard the small passages are easily scored by a hard or too large of wire. I've also heard that badly clogged jets can be difficult to get clear without passing a wire through, so I'd probably try passing something soft/thin through after cleaning but before reassembling to be sure it's clean & open. Then use more aggression as required!<br /><br />Check this out...<br /><br />9.9/15 hp maintenance repair article <br /><br />Oh, and check that nothing is funky with the throttle linkages and gears in the tiller arm, I had to fix mine up when I got it. They were so worn that the cogs could jump.<br /><br />good luck!<br /><br />Brent

Re: 1979 Evinrude 15hp poor idle

I cleaned the carb last night, it appeared to be just fine. I blasted air & Carb cleaner through all the idle jets, and reversed the flow as well.<br /><br />Everything looks great. I did notice however, the throttle roller is well disengaged from the cam on the timing plate when the throttle is twisted and approaching the idle stop adjustment screw. By design, it appears the low speed is totally a function of controlling the timing, and not the carb at all.<br /><br />This tells me the carb was fine after all, and I possibly have a timing or ignition issue instead. <br /><br />I have a new question based on this info: with the engine not running, the cover off, and in gear, if I twist the tiller handle through the entire range from idle through wide open throttle several times, the flywheel turns with the ignition plate just a little bit. Is this normal?<br /><br />Finally, how do I check the timing on this guy?

Re: 1979 Evinrude 15hp poor idle

Marty,<br />I have the same motor-year. Just for grins I looked at my linkages and see that the carb throttle roller sits just at the end of the advance plate on the right hand side. There is no movement of the flywheel when I fully advance the throttle from the idle position. Perhaps you have a coil under the flywheel mis-adjusted and slightly contacting the flywheel. I would think it odd too if the flywheel moved , while in gear, when you advanced the throttle. You would be moving the entire drive train, pistons,crank,drive shaft and lower unit. Even in neutral, I wouldn't expect to see the flywheel moving unless theres a slight amount of slop. Have you pulled the flywheel?? Check to see that the crank/flywheel key hasn't sheared. I would expect the motor to be backfiring and way out of time if the key was sheared. If you do remove the flywheel, be sure you clean both the crank taper and flywheel taper, no oil or lubrication, just clean and dry assembly and then torque it to specs.<br /><br />The throttle cam adjustment is pretty easy. <br />To adjust the throttle pickup, advance the throttle control until the roller is centered between the 2 cam marks on the advance cam. Back out on the cam follower adjustment screw (Phillips screw) until the throttle valve is completely closed. Then advance the screw until you see the throttle shaft just begin to rotate.<br /><br />BTW, try not to double post. Keeping all of your eggs in one basket , so to speak, makes it easier to get you the info you need.

Re: 1979 Evinrude 15hp poor idle

Ok, I'm a little uneducated as to where these two marks you are referring to are...

Re: 1979 Evinrude 15hp poor idle

OK, you mentioned 'Throttle roller" , this roller rides on the Advance Cam . Near the right hand side of the Advance cam, you should find the 2 hash marks. Turn the throttle handle until the 2 hash marks are centered directly behind the roller. Turn the phillips screw adjustment on the roller arm until the butterfly of the carb just starts to move, you're done. These adjustments are clearly mentioned in the manual. If you plan on keeping the motor, it would be a wise investment. I'm sure you know you can order manuals from the link at the bottom of this page.

Re: 1979 Evinrude 15hp poor idle

On my motor, the cam has a single triangular mark only. I lined it up with the roller and adjusted it per your advice.<br /><br />Have you ever heard of this roller wearing out? This one has a lot of play it it.<br /><br />It still runs rough and stalls after trying to idle the motor. <br /><br />I took the entire timing plate off today and cleaned it up and relubed the surfaces with synthetic grease. After reassembling, I was rotating the flywheel back and forth a few degrees for no real good reason, and heard something I did not like, it sounded like a whole lot of rod bearing play. <br /><br />So I did a compression test. It came up with less than 50# with one pull of the entire length of the starter rope.<br /><br />I think what I have here is one very tired engine that is ready to blow a rod. I ran it with the cover off (with muffs, of course) and it has a very definite rod noise. <br /><br />I think the compression is so low the engine simply cannot idle. I know this, it pulls over a lot easier than my very low hours 1968 9.5hp Johnson.

Re: 1979 Evinrude 15hp poor idle

To:<br />BF <br />Captain <br />Member # 21188 <br /><br />Thanks for the link for the online "how-to" sheet for the 15hp. Due to you sending me the link, I discovered my lower unit drain was plugged and fixed it according to the directions in the link.<br /><br />Thanks again!

Re: 1979 Evinrude 15hp poor idle

Marty,<br /><br />Yes, I'm sure the roller can wear considerably , along with the whole cam follower assembly. The point of aligning the roller with the mark on the advance cam and adjusting the Phillips screw is to remove the slop in the linkage so you'll have a zero lash condition and a synchronized ignition. If the motor has many hours, overheats, improper lubrication because of improper fuel/oil mix, running too lean , or general neglect, you're looking at an overhaul. The only real way to know the condition of the power head is to open it up and have a look. Only then , can you make a decision on wether it's worth rebuilding. Running it until it throws a rod thru the block will magically transform it into a boat anchor. These older motors are pretty much bullet proof if reasonable care has been taken with regular maintainance. Open the power head, you may be mildly surprised to find that all it needs is some new rings and some bearings , etc. . On the other hand you may gasp in wonder, and ask youself.... ...How did this thing make it THIS far?? Good Luck

Re: 1979 Evinrude 15hp poor idle

Thanks a million for the help. I put my old trusty (but slow) 9.5hp Johnson back on and am about to tear into the 15.

Re: 1979 Evinrude 15hp poor idle

I opened it up!<br /><br />Problems I found:<br /><br />1. Piston rings are so loose the pistons nearly fell out after removing the connecting rods from the crank.<br /><br />2. Top piston wrist pin bearing has a couple of chunks broken off the side of the cage. (probably from a poor assembly job)<br /><br />3. The top of the top piston has a couple small dents on the exhaust ramp.<br /><br />4. Both rods exhibit excess bearing play at both the wrist pins and crank, with the #2 being a lot worse.<br /><br />5. I broke off a bolt in the block from the exhaust cooler cover plate. Now I get the opportunity to fix that too. Great.<br /><br />QUESTION:<br />Should I replace the pistons, rods, & wrist pins in addition to the bearings and rings? (A good friend of mine who is heavy into 2-stroke liquid cooled cart racing suggested I replace them)

Re: 1979 Evinrude 15hp poor idle

OH! There's more:<br /><br />Someone had removed the thermostat from this motor a long time ago. The excess build up of crapola is the indicator I used to determine it was a 'long time ago'.<br /><br />Also, the small rubber gasket in the exhaust stack, which seals the copper water pump supply tube to the crankcase, was deformed with one side of it pushed into the hole in the crankcase, severely restricting the flow of water. Gee, I wonder why this 'trolling motor' needs rebuilding?<br /><br />I will be taking some measurments to determine wear issues tonight.

Re: 1979 Evinrude 15hp poor idle

Hey Marty,<br /><br />Sorry to hear that you've got major mechanical issues, not just adjusting/cleaning. Thanks for the updates, and please continue to keep us posted, I'd like to hear how it's going.<br /><br />As for what parts to replace... I'd let the condition of the pistons tell me whether they'd be done or not. Rods I'd leave, unless there's some reason to be concerned about them. <br /><br />On a snowmobile I used to have, I was concerned that the rings were due to be replaced. It ran good and had decent compression. I just knew they were original and the motor had lots of miles on it. A 2 stroke motor guy I knew suggested I get new pistons & rings and go 1st oversize (get the cylinders bored out) to make everything perfect. I respectfully decided to keep the pistons, not over-bore, and just replace the rings and lightly hone the cylinders. I used it another 2 or 3 seasons afterwards (sold it still running strong) and was always glad that I hadn't spent more $$ than needed or monkied more with a motor that had always been good to me.<br /><br />I know it's not exactly the same... but it's just my experience of ignoring someone's advice about replacing more parts. Measuring the wear on the block and pistons will help you decide.<br /><br />Good luck.<br /><br />Brent

Re: 1979 Evinrude 15hp poor idle

Ok, here's the skinny:<br /><br />Piston skirts are .0075" and .0085" larger than measurement taken from the bottom 1/3 of the bores. I don't know what the spec's are, but I have never heard of a piston skirt clearance spec larger than .005", and they are usually around .003-.004".<br /><br />Also, the bores are egg shaped at the top and it will take a .010" over piston to straighten things back out again. <br /><br />So, the new questions are:<br /><br />1. What are the actual spec's?<br /><br />2. Can I buy .010" over pistons?<br /><br />More update:<br /><br />Someone has been into this motor before. Apparently whoever it was, fractured a long narrow section off the top of the web separating the exhaust chamber from the coolant chamber and added som weld to build it back up. it looks pretty nasty, but they somehow machined it flat, and the gasket and sealer seems to have been doing the job.<br /><br />There is a lot of crusty crap in all the coolant areas. I will scrape out as much as is practical to induce better cooling, but I am more concerned about flow, than anything else. Once I properly install a new rubber washer at the top of the copper tube, I'm sure flow will not be a problem.<br /><br />Once I removed the exhaust baffle, more of the broken bolt was exposed to permit trying to remove it. I was able to turn it back in about 1/16 turn when the last piece of the exposed bolt also broke off. These are pretty soft bolts. I am now forced to do the drill and extractor exercise, with the possiblity of graduating to a helicoil. The only problem there is that there isn't a whole lot of casting surrounding that particular bolt. More news on this later.<br /><br />I won't continue on this motor until after I find out if oversize pistons are available. I won't buy them even then until I am successful in removing the broken bolt.<br /><br />I keep you posted...

Re: 1979 Evinrude 15hp poor idle

Latest news:<br /><br />I successfully removed the broken bolt and found a place to bore the cylinders out.<br /><br />But I have a new question:<br /><br />There is a red/brown primer colored paint on the interior of the crankcase which is flaking off. Is this a factory application, and if so, why is it there?<br /><br />I will use a small s.s. wire brush to scrub the interior of the crankcase to remove the loose stuff. I can't believe it would be good on the bearings to have that stuff floating around in there.

Re: 1979 Evinrude 15hp poor idle

That coating is actually there to prevent seapage of fuel/oil through the casting. OMC castings are notoriously porous and over time there would be an oily residue on the outside of your motor casing. That coating is an attempt to seal it all in...<br />- Scott

Re: 1979 Evinrude 15hp poor idle

Here's the latest news on my 15 'Rude...<br /><br />I finally found the time to finish it. It now has new everything - rings, pistons, wrist pins, rods, crankshaft, all bearings and seals, waterpump, and the list goes on & on. <br /><br />I was able to get the broken bolt out of the exhaust coolant chamber, and then remachined the entire surface flat again on a bridgport. The repairman of the welded web must have used a file to 'machine' the weld flat becuase it was .008" low in that area. <br /><br />I'm breaking it in right now, have run 1 gallon of 24:1 mixture and then one gallon of 32:1 mixture. It was too cold out to be out there any more today: 40 degrees, drizzly, and NO sunshine whatsoever. I'm doing the accepted break-in: no WOT until 5 gallons of gas is through it. <br /><br />With just 2 gallons there is a marked improvement in acceleration - even at 1/2 throttle.<br /><br />It idles down pretty darn good with the idle speed adjustment about where it belongs, and not cranked nearly all the way out like it used to be.<br /><br />It does have a definite bumpety-bump miss, but hopefully that will dissappear with 50:1 fuel/oil mixture.<br /><br />How much $ to rebuild it so far? I'm too embarrased to say...suffice it to say I know a lot more about purchasing a used boat motor than I did before. I'll never buy another one without *personally* performing a compression check.