Early 80s 40 hp

[hardwater fisherman]

Canadian made tiller model with rope start serial number 7207752...The previous owner had 370 dollars of work done in 2018 and the motor was not used this year. The work done was a new impeller, gear oil change, carb cleaning and new spark plugs.The picture is the plugs I removed from the motor after buying it on Friday.. The motor has 150 psi on both by my gauge.. And good strong spark of 7/16 on both.. I replaced the plugs and have been running it on muffs and now in a large tub... The top plug is turning black like before and the bottom is still white.. Does this seem like an ignition problem? Also what is a good RPM for shifting out of neutral? My tub is deep enough but not big enough to run it in gear.. I read that it should idle in gear around 650-700.. I can get it to idle around 780 in neutral so maybe I am okay?

 

[jimmbo]

A good rpm for shifting is the lowest speed where the engine will not die when placed in Gear. Usually that results in an in gear Idle speed of 600 - 650.

I would run a good Combustion Chamber Cleaner(Merc Power Tune, or BRP Engine Cleaner) thru the engine to clean out any carbon in the Combusion Chamber, and behind the rings.
Since both cylinders are fed from one carb, I doubt it is a fuel issue.
You need to put the motor on a boat, run it hard, then look at the plugs. Surface Gap plugs, being very cold plugs, can get a bit dirty when run at lower speeds with little load.
Puddled fuel in the lower crankcase is transferred to the upper cylinder to be burned and that might be causing the soot on the upper plug.

Wipe the dirty plug clean and swap them when you reinstall them, see if the sootjng goes with the plug or stays with the cylinder.
Or just buy a new plug and see what it does

 

[hardwater fisherman]

I am going to try to get it out on the water this week.. Probably Thursday.. I will try to find some of the engine cleaner, but I may have to order it.. I now remember he told me he had been running it at 40 to 1 mixture so that probably did not help.. I have been running it at 50 to 1 and it seems to idle smoother..

 

[Texasmark]

Mercurys I have owned were spec'd at 675 +/- 50 RPMs.............in the water at idle in F gear, boat moving. So your in the tank in N sounds good to me. 50:1 is the recommended 2 stroke ratio since way back in the 60's and if you use Pennzoil Premium TC-W3 2 stroke oil, your smoking will be reduced......Wally World sporting goods section has it.

Last, google or tap the archives here on "Decarb". Don't forget the new plugs part after the operation. Do that and then keep Sea Foam in your fuel (in addition to your regular method of lubrication) as per the label on the can....1 oz per gallon of gas. WW has that too in the automotive section.

 

[hardwater fisherman]

Thanks. I have done decarbs before on other motors using sea foam. And I do add sea foam to my fuel tanks.. I am not sure if I can find any of the OEM products that jimmbo talked about without ordering online.. We have one small Evinrude dealer that might have it.. Also there is a BRP Can Am dealer but they sell snowmobiles, seados ect. Not sure if they would carry it..

 

[hardwater fisherman]

New plugs I put in on Saturday.. At first the top one turned black.. I was still using the fuel that was in the tank that came with the motor.. I watched him pour the fuel into the tank so im pretty sure its fresh.. But when I switched over to my tank it seems to be running better and cleaner at idle. I will take it out on Thursday to see how it runs.

 

[hardwater fisherman]

My lake test started out okay... But just as the boat was up on plane it surged and then slowed down.. I could tell it was only running on 1 cylinder.. I then found that I have no spark on top.. I switched the coils and still no spark on top.. It passed a cylinder drop test on the weekend and showed good open air spark too.. Now nothing on top. Do stators or the trigger fail like this only on one cylinder? Or more likely the switch box? After i was able to get it started on the bottom cylinder I heard some arcing, but could not see from where.. The arcing stopped after a short time.. Thanks for any help.

 

[jimmbo]

Arcing sounds indicate a problem with the High Voltage end, meaning Coil, Sparkplug Wire, and Sparkplug. Perhaps try running it in the dark to see if the Arcing more visible. At night in a well vented area. Running it in a darkened Garage with doors closed during the day could result in the sound of the engine purring you to sleep, permanently

 

[hardwater fisherman]

I found a parts motor with electric start.. After testing the coils and stator and trigger with an ohm meter.. I tried the switch box off the parts motor, and now have spark on both..