Need opinions about 1973 18hp Evinrude-UPDATED

[dwagner47]

I purchased a 1973 18hp Evinrude in good physical shape a few months ago. The motor had a rebuilt carb and water pump. The motor started but hesitated on acceleration. After a few seconds at more than half throttle things clear up and the motor runs great with lots of power. Alot of unburned oil and carbon was coming out of the exhaust at lower speeds though. I did the following to the motor:
- Set carb float height
- Replaced points and condensers
- Set timing
- Synchronized timing advance and carb
- Replaced plugs
- Replaced sensor coil
- Replaced 1 of the 2 high tension coils (they seem OK)
- Replaced thermostat
- Performed decarb procedure
- Resealed lower unit

After the above was done and running on OMC oil and premium gas the motor runs much smoother but the hesitation on acceleration persists. The new thermostat seems to have solved the oil and carbon coming out of the exhaust so I think the motor was running too cool. The exhaust outlet water is hot to the touch and a infrared thermometer shows about 150 degrees on the cylinder head. After using the motor a bit I observe that when running half throttle or more the hesitation goes away after a few seconds and the motor runs great. When slowing down below half throttle the motor idles down nicely but after 30 seconds it sounds like it is missing and it gets more smoky. If I speed up again it hesitates for a few seconds and then clears out. The motor starts with a 1/4 pull when warm but when cold it will start when choked but it always stalls and requires several pulls to get going. My next thought was rings so I got a compression tester and each cylinder shows 105 psi. If I put a teaspoon of oil in and retest the results are 120 psi on each cylinder. If I peer into the cylinder through the spark plug holes I observe some discolorization on the cylinder walls by the exhaust ports but it is hard to tell if it is scoring. The motor is in good shape, after a touch up paint job it looks great. From looking at the wear on the driveshaft, propshaft and water pump housing I believe it has not been abused but has hours typical of a 1973 motor.

I purchased the service manual and went through all troubleshooting procedures. My next step would be to pull the head and consider replacing rings and maybe reboring the block. Some questions:

- Does the compression test and motor behavior suggest worn or stuck rings?
- Any other suggestions for the hesitation and missing behavior below half throttle?

I only paid $450 for the motor so I would consider investing a few hundred dollars in it. It has been a fun learning project so far. Thanks for any advice.[b]

[bigredfish69]

be sure your using 16 oz of oil for 6 gallons of gas

[Paul Moir]

The compression test indicates that the engine is in good physical shape. You do expect a jump when you add oil. 15 PSI is about right to my mind. Stuck rings will show as very bad or uneven compression in my experience.

The hesitation suggests to me that the engine is running too rich or lean at idle. The excess fuel/oil suggests too rich as does the stall on start. Does any adjustment help?

When you had the flywheel off, was there any sign of oil up under the flywheel? If the top main seal was bad, it would leave a mist of oil over all the components up there.

Which spark plugs are you running? What gap? Do the firing ends appear the same after shutting down after idling a while?

One thing you might want to try doing is to disconnect the recirculation lines from the bypass covers, block the inlets of the bypass covers and see how it runs then. Perhaps this is a loading up problem. Someone more familiar with the 18hp set up to burn the pooled fuel could probably provide more useful comments in this regard.

[F_R]

yeah, Paul knows about those motors, but he ain't saying.
The little hose going to the bypass cover carries excess fuel that has settled in the crankcase. That settled fuel causes what is called "loading up". The hose going to the bypass cover dumps the fuel into the cylinder where it is supposedly burned, in theory anyway. What actually happens is it makes it idle lousy due to being too rich on that cylinder.

Earlier models dumped the excess fuel into the exhaust stream, where it wound up in the lake. That caused objections from environmentalists. But they sure did idle better! Now, some people converted motors like yours back to the earlier version to make them run better. I know an easy way to convert them, but I ain't talking either. Well in public anyway.

I might add that merely plugging the hose doesn't help much because that just makes the fuel puddle up in the crankcase. You gotta get rid of it.

[Paul Moir]

Some people converted the earlier, larger engines to pump the (otherwise recirculated) fuel back into the fuel tank through a second hose in an attempt to improve fuel economy. There are compelling reasons why you shouldn't do that, such as contamination of the fuel and that it would effectively enrichen the oil ratio. But it might be worth considering as an alternative.

As for the fuel savings, I belive they didn't amount to much unless there was something wrong with the engine to start with.

But please understand, this is purely for those who enjoy fiddling with engines. No guarantees!

[dwagner47]

Thanks everyone for the feedback.
- Plugs are the standard Champion J4J or equiv. gapped at .030
- My mix is accurate 50-1.
- I've played with the low speed mixture making richer until the motor doesn't sneeze any more.
- Both plugs are the same after running in the rich condition. They are not sooty but they are not brown either.
- The top crankshaft seal is not leaking, everything on the armature plate is nice and clean.

When the motor is "loaded up" it is definitely running rich. It is almost like the low speed is too rich but the motor will start sneezing if I lean out the mixture.

So my compression test is OK? It would be nice if I didn't need to pull it apart now.

I'm not sure what to do next about the hesitation issue.

[steelespike]

Be sure when you adjust the idle mixture it is in gear warm and rpm is around 650 rpm.Be patient when adjusting especially when going from sneeze to smooth idle.I wonder if it was adjusted just a little toward sneeze
if it would load up soon enough to make it more normal.
I know we want to be careful about too lean an adjustment but it appears it would load up to a more normal operation quickly.
Check the sync adjustment.You might double check the float adjustment. though it doesn't seem likely.
As allready stated it could be the recirc. lines.

[F_R]

Make sure the carb throttle synchronization is correct. Then adjust the idle mixture rich enough to prevent sneezing. That's about all you can do and you more or less have to live with it. The fact is that one cylinder is leaner than the other due to dumping the puddle line into one of them, making that one richer. The leaner one sneezes if you try to adjust it out.

The only other solutions are to catch the recirculating fuel as suggested by Paul, or retrofit it to the c.1968 system. We had trouble satisfying customers when these motors were brand new, because they wouldn't troll worth a hoot.

[tashasdaddy]

don't know if you've red this

http://www.iboats.com/bbboard/bbBoar...98;gpid=818802

[Chinewalker]

Skip the premium fuel and run 87 octane...
- Scott

[dwagner47]

Thanks for the good advice, I am very pleased with all the helpful responses.

I'm surprised that these motors would be so tempermental as to never idle smoothly. I also would expect the plug of the top cylinder to show some evidence of running to rich if the recirc line is causing the problem. The info does give me something to focus on before pulling the heads or disassembling the motor.

How do the newer OMC crossflow motors deal with the recirc issue and still have good idle? I'll have to double check but I have a 2000 9.8 hp Nissan outboard that looks to be a very similiar design that idles like a dream.

My local shop showed me a bulliten for the OMC motors about plug fouling and rough idle. The solution was to plug the bypass hole by the thermostat that resulted in the motor running at a higher temp. I tried this and when starting the motor very little water comes out the exhaust initially. When the motor warms up the normal amount of water is discharged but the water is quite hot and the motor puts out alot of steam. The hesitation problem may have been slightly less but the issue was still there. I didn't know if I could be overheating the motor so I took the plug out.

Could the recirc line not be working causing the extra fuel to puddle more in the intake area? When taking the hose off I seen spitting of fuel from the intake manifold and I observe vacuum on the cylinder. The hose looks OK but it may be constricted slightly where it bends just before attaching to the nipples on the intake manifold and the upper cylinder. Also, could a leak between carb and intake manifold cause this issue? The carb was rebuilt but the gasket between carb and intake is old.

[DJ]

The gasket should be changed. However, if it were leaking you would have a lean condition, which you do not have.

The Nissan may be loop charged-not sure. If so, it's a different animal.

Another suggestion may be to "capture" the recirc. (oil/gas) mix in a small container in the lower cowl. It won't be much over a day period.

You do not need to tear into that engine. Your compression readings indicate a very healthy engine. You've done all the right stuff. As mentioned prior, they never did idle that great. It sounds like there are ways around the issue though.8)

[dwagner47]

Tashadaddy - I have read the thread on setting the low speed mix - very helpful. I also bought (and read) the service manual and numerous books. This has been a fun project but it would be nice to have an old outboard that looks great and runs great!

Chinewalker - My OMC dealer showed me a bulliten which discussed the effects of unleaded gasoline on these older motors and it recommended higher octane. I do notice that the motor runs better on 93 vs 87 octane.

DWJ - The Nissan looks like a crossflow design. It is very simple - I expect that's why it's a 10 hp motor that weighs 58 lbs. I do understand what you mean by these motors not idling perfectly. I recall a 1980s vintage Johnson 35 hp that did alot of shaking and sneezing at lower RPMs but it never hesitated. On the other hand I had a 1969 Johnson 6 hp that would idle down to nothing. I wouldn't mind a little roughness at idle but my 18 hp hesitates every time upon acceleration and always runs very rich and is smoky at lower speed running. I can't believe it ran that way when new.

Thanks again for all the advice - I've got a few things to tinker with to see if I can improve the issue.

[capngregg]

I'm new to this website and I just read your problem and all the responses. Ain't boating great?

I'm not as familiar with the Evinrudes as some of the other two strokers but have you verified the condition of the reed valves? I've seen some that have chipped and/or worn away in small areas that caused some of the conditions you're seeing. Also ensure that the idle and main jet circuits are not eroded.

[DJ]

Chinewalker - My OMC dealer showed me a bulliten which discussed the effects of unleaded gasoline on these older motors and it recommended higher octane. I do notice that the motor runs better on 93 vs 87 octane.

Be aware that todays gasolines do not have the same characteristics of gasolines found in the 70's.

Higher octane fuels run cooler. That is what octane does-it cools the combustion process to eliminate detonation. Higher octane fuel will only add to the smoke issue/foulining issue. I have never, nor ever will run more than 87 octane in any of my outboards.

The only other solutions are to catch the recirculating fuel as suggested by Paul, or retrofit it to the c.1968 system. We had trouble satisfying customers when these motors were brand new, because they wouldn't troll worth a hoot.

Remember, this is a 33 year old engine with 33 year old technology. Comparing to a 2000 model is not a valid comparison. Also, your 9.8 and your 6 are much smaller displacement. The 18, 20, 25, 28, 35 were fairly large displacement for a 2 cylinder engine. Getting a complete combustion in a larger bore cylinder is much more difficult than a smaller one.

Idling creates unburned product that the recirc was designed to deal with. The recirc. was a mandatory method of dealing with unburned fuel. Did it work?, Sort of.

It has been hinted at as to what to do with the recirc.

[G DANE]

The 18 can iddle real good. However it takes a perfectly adjusted ignition as this is the low tension point/condenser type. Make following up to par: Both set of points hould open exactly 0.020 Inch when on "set" mark on cam. Distance between coil ends and magnets in flywheel is critical. There is an OMC tool called an ignition ring that makes it possible to measure when flywheel off. I havnt got it, but takes measure of the turn marks on the bosses on armature plate, do a little trial and error and that does the trick. Be sure to have two good condenser/point sets in. Set and adjusted correct ,this ignition will work perfect for many hours. Now adjust your carb. The tricky is, that with this ignition, ignition trouble can seem like carb trouble and the other way around too. A weak ignition can make it load up at iddle. Your comment about the 6 HP: I've seen no other motor that can iddle like a 6 HP fisherman, except the 4 strokes, that 6 is a gem. When you got your 18 tuned in right, you will love it, they are VERY smooth runners.

[dwagner47]

Capnqueqq - The dealer told me that bad reeds would cause spitting back through the carb. I don't observe this.

DWJ - Interesting point about high octane fuel. Contrary to the dealer's opinion but it makes sense. Although when reading on a lawnmower board someone said high octane will make an air cooled engine run hotter. I now understand some options to try with the recirc. I can recheck timing, synchronization, float level, etc. The funny thing is that the hesitation and loading up has not changed one bit between the time I first tried the motor and after all the tune up work. The motor now runs smoother and starts effortlessly when warm and the new thermostat and decarb has eliminated the black stuff coming out the exhaust but the hesitation has not changed a bit.

G DANE - Encouraging that the 18, 20 & 25s can be tuned to run smooth. I was very careful setting the point gap and timing using the set mark on the cam. Coil-magnet distance I set by lining up the coil housing with the bosses on the armature. I replaced all the coils (one of the external ones was cracked) to rule out a weak ignition - this did not make any difference

This has been a fun but challenging project. These older outboards appeal to me probably because I grew up pouring over the new outboard reviews back in the 1960s and 1970s.

Here's a question - what is the difference between my Evinrude 18 and a Johnson 20 of the same vintage? They are both rated at the same RPM. Did they have a different high speed jet or is the hp numbers just for marketing?

Thanks again everyone - what a great forum!

[iwombat]

Another thing to try is fiddling with the plug gap and maybe trying a hotter plug. That won't help the recirc issue, but may help you get that nice slow idle you're looking for.

[Solittle]

Your symptoms point to crud in the carb despite what the seller told you about it being rebuilt.

[dwagner47]

Solittle - I have totally disassembled the carb and it is clean as a whistle with brand new float, needle and gaskets.

I've been through the motor from top to bottom excluding pulling the head or intake manifold.

[G DANE]

I Would start with a spark test, I battled with a 1973 25 HP almost an entire spring. The true problem appeared when I made a spark test, makin both sparks jump longer and longer gap, just to find one was weak. Turned out that one of the new condensers were weak. With that fixed and coils as near to magnets as possible, and a correction of armature plate wobble, it ran like new and still does. Before it used to shake and cut out at iddle, hisitate on low end at hole shot, and plugs shoved it loaded up.

[dwagner47]

G DANE:
Your advice rings true somewhat as once I was trying to do a crude spark test and I observed that the motor idled better when I held the spark plug boot around an inch away from the plug versus when it was on the plug snug. This confused me as I didn't know if it pointed to a spark problem or timing issue. As I had already replaced the points & condensers and set timing carefully I didn't think that would be the problem. I assume I can do a spark test by putting something conductive in the spark plug boot and observe the spark jumping to the plug while running? Doing this what constitutes a weak versus strong spark? How can I measure the gap between the flywheel magnet and sensor coil? I was just lining up the frame of the sensor coil with the bosses on the armature currently.

[iwombat]

Almost . . .

You'll want to watch the spark jump to the block, or something grounded to the block, not the plug end.

Something like this, or you can just make your own.

[iwombat]

In case you haven't seen one before. That's a ground clip at the bottom and an adjustable screw in a c-mount, with a spark plug sized connector on the very top.

You attach the clip to the block, adjust the screw to the correct gap, and attach your plug wire to the top.

[iwombat]

All that being said, you can also just shove a bolt into the spark plug boot and attempt to hold it a fixed distance from the block. It's far easier using a proper tool though.