50 HP 2-stroke

Motor will not start

Have a question about your motor? All motor talk and questions go here.
Post Reply
User avatar
Duke62
Posts: 121
Joined: 22 Dec 2012, 22:59
Location: Dallas, GA

50 HP 2-stroke

Post by Duke62 » 09 Sep 2019, 06:45

I have a 1985 Mercury 50 hp 2-stroke that will not start. I have replaced the stator, impeller, spark plugs, all fuel lines, fuel filter, and the carbs/fuel pump was rebuilt. The motor started and ran good in the driveway. Took it to the lake, started off the trailer. Went fishing and moved 3 times. On the fourth time the motor would not start and hasn't started since. It turns over and sometimes tries to catch, but will not start. What should I try next?
United States Air Force (Retired)
1973 Seacruiser 14 ft conversion (glass) http://www.tinboats.net/forum/viewtopic ... 21&t=28559
1985 Bass Tracker Refurb https://www.forum.tinboats.net/viewtopi ... 28#p440638

RazorBaits
Weldorthemagnificent
Posts: 770
Joined: 12 Mar 2017, 12:09

50 HP 2-stroke

Post by Weldorthemagnificent » 09 Sep 2019, 17:37

An Evinrude! Lol. Sorry couldn't resist. Is the fuel fresh or old and smelly? Another thing to check is the spark. There are testers but I just use a spare spark plug and look for a hot blue spark not a weak orange one.

Sent from my CLT-L04 using Tapatalk


MrGiggles
Posts: 264
Joined: 12 Jul 2017, 21:42
Location: Springfield, MO

50 HP 2-stroke

Post by MrGiggles » 10 Sep 2019, 13:18

Did you check the basics? Spark, fuel, compression.

Will it run on starting fluid or a prime? If not, no spark or weak spark. If it does, you do not have fuel delivery.

I would put an adjustable gap spark tester and check for spark, it should jump 1/4" or so.

sdm111
Posts: 35
Joined: 09 Dec 2012, 18:25

50 HP 2-stroke

Post by sdm111 » 10 Sep 2019, 14:21

Sounds like its not getting fire

maintenanceguy
Posts: 97
Joined: 12 Dec 2018, 21:18
Location: South Jersey

50 HP 2-stroke

Post by maintenanceguy » 10 Sep 2019, 20:07

First, check compression. It doesn't tell you everything about a motor's condition but it's a good indicator that a motor is worth fixing or not. Best case: I would be pleased if all cylinders are within 10 psi of each other and compression 120psi or better. I could live with at least 100psi compression and all cylinders within15%. Below this, I'll tinker with it but I don't expect much.

Second, verify spark. Spark testers can be had for under $15 at your local auto parts store. If no spark, you have to work your way through the electrical system. There are lots of kinds of ignition systems - you'll need to find the instructions for troubleshooting the one specific to your engine.

Third, verify that you have fuel in the carburetor's fuel bowl. There is probably a screw you can remove on the side of the bowl and you should see fuel pour out. Or, remove the bowl and see if it has fuel in it. This proves that you have fuel at least to the carb, even if it isn't getting through the carb to the engine.

If you have good compression, good spark, and fuel to the carburetors, my next guess is dirty, plugged, or varnished (from evaporated fuel) carbs. I would remove them, disassemble them, clean them, and replace any jets, floats, float needle, seals, or other parts that seem questionable. After rebuilding, find instructions on adjusting the air idle screw on your carb. Usually, you turn it in to gently seat (valve now closed) and turn it out 2 full turns. Hopefully, the engine runs and you turn it in or out until you hit the sweet spot where it sounds the best at idle.

If you can feel air blowing OUT of the carbs in puffs when the motor is turning over - suspect damaged or bent reed valves - this is unusual but it happens.

Lots of other things can go bad but I think this covers the most common issues.

User avatar
Duke62
Posts: 121
Joined: 22 Dec 2012, 22:59
Location: Dallas, GA

50 HP 2-stroke

Post by Duke62 » 14 Sep 2019, 17:19

Completed compression test 120 all four cylinders. Performed spark test, all four have spark. Bulb is pumping full through the line, fuel is pumping when motor is turned over. Removed carb bowls, plenty of fuel getting to the carbs. Carbs were rebuilt 2 months ago. Gas is only a couple of months old. Tank and all fuel lines are new. Stator, switch box, and plugs replaced two months ago. It makes no sense. I cranked it 5 times in the driveway and let it run random amounts of time the night before I took it out. When I took it out the next moring it stared off the trailer. I fished and moved spots three times. Then on the fourth move it would not start. And has not started since. I can't find anything wrong. It turns over but will not crank.
United States Air Force (Retired)
1973 Seacruiser 14 ft conversion (glass) http://www.tinboats.net/forum/viewtopic ... 21&t=28559
1985 Bass Tracker Refurb https://www.forum.tinboats.net/viewtopi ... 28#p440638

Weldorthemagnificent
Posts: 770
Joined: 12 Mar 2017, 12:09

50 HP 2-stroke

Post by Weldorthemagnificent » 15 Sep 2019, 06:54

Is the fuel in an onboard tank or a portable? If there is good spark, fuel and compression... I'd be looking closely at that fuel. I've seen fuel come out of ATVs and snowmobiles that wouldn't burn when poured on the door and a lighter held to it.

Sent from my CLT-L04 using Tapatalk


The Hamilton Guy
Posts: 17
Joined: 05 Aug 2019, 11:36

50 HP 2-stroke

Post by The Hamilton Guy » 15 Sep 2019, 07:22

Given everything else checks out, I’d wonder if he jets in the carb got plugged.


Sent from my iPhone using Tapatalk

Weldorthemagnificent
Posts: 770
Joined: 12 Mar 2017, 12:09

50 HP 2-stroke

Post by Weldorthemagnificent » 15 Sep 2019, 10:08

Good point. Are the plugs wet after trying to start it?

Sent from my CLT-L04 using Tapatalk



User avatar
Duke62
Posts: 121
Joined: 22 Dec 2012, 22:59
Location: Dallas, GA

50 HP 2-stroke

Post by Duke62 » 16 Sep 2019, 09:30

Weldorthemagnificent wrote:
15 Sep 2019, 06:54
Is the fuel in an onboard tank or a portable? If there is good spark, fuel and compression... I'd be looking closely at that fuel. I've seen fuel come out of ATVs and snowmobiles that wouldn't burn when poured on the door and a lighter held to it.

Sent from my CLT-L04 using Tapatalk
Portable tank
United States Air Force (Retired)
1973 Seacruiser 14 ft conversion (glass) http://www.tinboats.net/forum/viewtopic ... 21&t=28559
1985 Bass Tracker Refurb https://www.forum.tinboats.net/viewtopi ... 28#p440638

Weldorthemagnificent
Posts: 770
Joined: 12 Mar 2017, 12:09

50 HP 2-stroke

Post by Weldorthemagnificent » 16 Sep 2019, 18:52

Will it run on gas squirted in the carbs?

Sent from my CLT-L04 using Tapatalk


Post Reply