Larger 2 stroke outboard and trolling question

[ShoestringMariner]

I’ve heard that older, larger 2 stroke OB’s don’t like running at trolling speeds for periods of time. My ‘76 650 merc is one of them, however last fall we trolled for staging salmon with it on Lake Huron and it never ran better. In 70deg water and summer weather, it acts up within 15 minutes. The water on Huron was 54 degrees and we ran it all day without anything but a minor hiccup and only one stall. (Weather was also pretty brisk)

It did load up a bit. We didn’t put the hammer down to come in (trolled in) and there was a fair bit of chocolate milkshake oozing out the exhaust.

So my questions are;
a) Does cooler weather and water temps typically make that much difference?
b) Will I do damage to this motor with extended periods of trolling these cooler weather/water situations? (I use Electric’s through the summer on smaller waterbodies anyway)

 

[racerone]

Trolled with a 1982 235 HP V-6 in Lake Huron myself in spring and summer.-------Hour after hour and no issues.-----Parts and pieces do not know how big the motor is that they are installed on !!

 

[dingbat]

I troll in water temps down to 35 F on a carbureted 200

Make sure the the engine is well tuned and the stats operate correctly.

May have to play with oils for best performance. If I run anything else other than a synthetic blend I get oil (white creamy) build up on the exhaust outlets by the end of the day

 

[ShoestringMariner]

Thanks guys.

dingbat, I run amzoil synthetic with a shot of Lucas in everything I own.

 

[JimS123]

Been there, done that. Oils make no difference. Many recommended Pennzoil full synthetic, but that was worse than any other. Ended up with OMC 50 semi-syn as the best for my application.

However, success came after installing Split Fire plugs. Smoke disappeared completely and the plugs ran clean for years after that.

I know I'll get a zillion poopoos with this recommendation, but it was an amazing lifesaver for me. I put on over 600 hours running time after the switch with not a single fouled plug.

 

[Sea Rider]

The water and air temp makes no difference as long the thermostat is doing its homework right. All 2 strokes smokers will foul plugs in the short run as when trolling for long time periods. If you throttle a motor say 3/4 to full throttle after been running at prolongued throttle speeds sometimes will tend to miss or will not pick rpm fast.

The tech issue is that at very low speed the plugs are not reaching their self cleaning temp which is achieved passing 500 deg C. That's why it's mandatory to run the motor full hammer down as if stealing the combo for some time specially when returning to Terra Firme as to burn the oil which has collected on the plug tip due to slow throlling speed working temp.

Happy Boating

 

[Chris1956]

A lot of those older Mercs do not have thermostats. My '73 Merc 850 and my '77 Merc 1500 didn't have thermostats, and they are also not included on most Merc inline motors of the 70s and 80s.. My Mercs ran dead cold at idle and warmer at cruise.

Some Merc models of the 70s and 80 had thermostats, although it was not a lot of models. Not sure if you have a 'stat on that 650.

The best way to achieve a good idle on your motor is tune your idle mixture screws to run best on fresh 50::1 fuel and to mix your fuel just before you go out.

 

[racerone]

A well tuned 2 stroke does NOT foul plugs.-----The whole concept is misunderstood I think !

 

[Sea Rider]

A well tuned 2 stroke does NOT foul plugs.-----The whole concept is misunderstood I think !

I see plug fouling often at my boating club mainly in boats that are used to take passengers from the pier to their boats and back again while their 2 strokes modern motors are run at displacement speeds. It's a temp related issue.

My horse doesn't like to be run at non planing speeds for more than 10 minutes which never do, he runs as a champ 3/4 to full tottle grip during each outing.

BTW, I'm talking about 2 strokes, 2 cylinder motors, larger 3-4-6-8 cylinder motors could behave much different as has more plugs and one carb per cylinder and that could make the big fouling/non fouling difference.

Happy Boating

 

[racerone]

If plugs are indeed " fouling " you should fix the issue !

 

[JimS123]

If plugs are indeed " fouling " you should fix the issue !

Run any OB at idle speed and 50:1 for hours and hours and if you don't have fouling its because you deviated from the norm. Now I'm talking about pre-mix gas.

If you have a newer motor with oil injection, and all is well with the engine, things may be different.

 

[racerone]

Ran a 1963 model 10 HP at 24:1 fishing / trolling for hrs.-----Never a hint of this " fouling " that is talked about.

 

[JimS123]

Ran a 1963 model 10 HP at 24:1 fishing / trolling for hrs.-----Never a hint of this " fouling " that is talked about.

My 1955 10 HP gave me the same results. I dunno what the difference is. But later motors fouled unless the spark plugs were tuned to improve the combustion.

Maybe the phrase "they don't make them like they used to" fits in here.

Als I know is that them there 4-strokes really run great.....LOL.

 

[ShoestringMariner]

Ran a 1963 model 10 HP at 24:1 fishing / trolling for hrs.-----Never a hint of this " fouling " that is talked about.

I’ve got a 58 10hp OMC and a 57 18hp OMC, both at 24:1 and same thing...zero problems all day, but I’ve heard the 25-35hp OMC’s of the same era don’t like trolling (got this from a collector...not sure if actual fact)

 

[Sea Rider]

In modern 2 strokes motors when plug fouling has occured while using 50:1 pre mix ratio. Can someone share his experience about the behaviour of their motor when that happened or when going from a slow throlling rpm to a higher rpm range as to plane the combo out of the hole fast enough.

Does throlling rpm means neccesarily that the throttle position is set at the min idle rpm range of that motor for that sole purpose ?

Happy Boating

 

[dingbat]

In modern 2 strokes motors when plug fouling has occured while using 50:1 pre mix ratio. Can someone share his experience about the behaviour of their motor when that happened or when going from a slow throlling rpm to a higher rpm range as to plane the combo out of the hole fast enough.

Does throlling rpm means neccesarily that the throttle position is set at the min idle rpm range of that motor for that sole purpose ?

Happy Boating

I troll Mercury, Evinrude and Yamaha outboards, 175 HP and up. All auto-oiling systems.

Typically troll at speeds between 750-900 rpm depending on conditions. The Evinrude, my personal motor, is set up to idle at 750 rpm just for that purpose.

During season, we troll 6-8 hours a day, 7 days if weather allows. When done for the day, I kick the motor our of gear and let it idle (Typically takes 15-20 minutes) while we get everything pulled in and stored for the trip back to the dock.

The Merc loads up a bit more but the Evinrude comes right out of the hole without hesitation. It's loaded up (ever so slight miss) but it smooths out within a couple of seconds of putting the hammer down. Purrs like a kitten on the 10-15 miles run back to the barn

 

[racerone]

This " fouling " of sparkplugs is not well understood I guess.-----When a motor acts up some automatically say ' plugs must be fouled " and do no trouble shooting !

 

[Sea Rider]

Will not speak for all motor brands if fouls plugs or not as don't own them all, but will agreed with what Dingbat says about a slight miss or hesitation that cures itself when full throttle is applied, my horse does same. Other important fact to consider is that auto oiling motors mixes very little amount of 2 strokes oil when running at very slow rpm compared to a pre mix motor that's always running at 50:1 whether at idle of full hammer down and that makes a big difference in the plug fouling scenario.

For me there's nothing to troubleshoot or adjust as plainly understand how the plug tip temp difference can affect a motor. If you've been in a 2 strokes motorcycle race, when all racers are aligned in a row prior to flag down, will notice that all are constantly throttling at high revs for the sole purpose not to foul the plugs and have a hesitation moment that could lead to lose precious seconds upon departure.

Racerone, in your case, are you still using 2 strokes motors with auto oiling systems or pre mix ones ?

Happy Boating

 

[JimS123]

In modern 2 strokes motors when plug fouling has occured while using 50:1 pre mix ratio. Can someone share his experience about the behaviour of their motor when that happened or when going from a slow throlling rpm to a higher rpm range as to plane the combo out of the hole fast enough.

Does throlling rpm means neccesarily that the throttle position is set at the min idle rpm range of that motor for that sole purpose ?

Happy Boating

Yes. Trolling at idle for hours and hours.

Then, when you finally accelerate the engine bogs down and sputters. It's not rocket science. When you pull the plugs its clear to see they are fouled. Put new plugs in (or clean the fouled ones) and its all OK again. For awhile. You can only clean fouled plugs so many times.

Its all about the 50:1 (or 24:1 before that). We all expected fouled plugs if we idled too long. Now, the variable ratio auto oiling has largely solved the problem. Also, back in the day, running hotter plugs on kickers was the general thinking, and that's why many outboarders didn't complain about fouling.

I grew up on the Erie Canal back in the 1950's. No wake zone the entire length. Anybody with twins ran one engine upstream and the other downstream.

 

[JimS123]

This " fouling " of sparkplugs is not well understood I guess.-----When a motor acts up some automatically say ' plugs must be fouled " and do no trouble shooting !

No, its well understood. At least by the old timers. The youngins don't run old premix motors so they have no experience. The visual of a fouled plug identifies the issue with few questions.