Question about Sport & Outdoor - Others

2 Answers

Engine runs rough when we throttle up

We have a 40hp 2 stroke Yamaha engine on our boat. It ran great then it started to run rough when we would increase the throttle. It was intermittent at first, now it is all the time. We changed the plugs, new gas filter,carburtor was taken off cleaned and adjusted . It worked great for about 20 minutes then we shut down and anchored. When we were off on our way again it started all over. Could this be an electrical problem.

Please help,

Posted by on


2 Answers

  • Level 1:

    An expert who has achieved level 1.


    An expert whose answer got voted for 20 times.


    An expert that has over 10 points.


    An expert whose answer got voted for 2 times.

  • Contributor
  • 10 Answers

Sounds like a spark plug issue. If the spark plug is not torqued after a good number of months it can seep at high rev sustained pressure. Otherwise I would look at the spark compensator or possibly the float.

Posted on Jan 02, 2010

  • Level 1:

    An expert who has achieved level 1.


    An expert that got 5 achievements.

    New Friend:

    An expert that has 1 follower.


    An expert who has answered 20 questions.

  • Contributor
  • 41 Answers

Hello, It could be ele. If you have ran cheap fuel in it and it has sit for a while, I would clean gas tank,lines, carb again, and run prem gas in tank.

Posted on Nov 25, 2008


1 Suggested Answer

  • 2 Answers

SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

A 6ya expert can help you resolve that issue over the phone in a minute or two.
Best thing about this new service is that you are never placed on hold and get to talk to real repairmen in the US.
The service is completely free and covers almost anything you can think of (from cars to computers, handyman, and even drones).
click here to download the app (for users in the US for now) and get all the help you need.
Good luck!

Posted on Jan 02, 2017

Add Your Answer

Uploading: 0%


Complete. Click "Add" to insert your video. Add



Related Questions:

1 Answer

I have a 40hp yamaha outboard it starts great but when i put in gear it stops

If it's a 2-stroke, have those carbs cleaned...
Then check if he runs on all 3 cylinders.

Aug 11, 2017 | Yamaha Boating

1 Answer

Jerking outboard engine

Good Day Khairul,
Are the Carbs Synchronized To Open And Shut At The Same Time?
If This Is Correct ! Then Do You Need To Pump The Primer To Contine Running?
If Yes Then Replace Fuel Pump DiaPhram
It Coud Still Be An Electrical Fault,
Coil,Trigger Or Stator .
Check To See Condition Of Plugs After Running,
Hope This Helps

Sep 10, 2013 | Boating

1 Answer

Free Mercury Outboard ONLY, 2-40HP 1965-1989 Repair Manual 1-2 Cylinder, 2 Stroke

I have a problem with my 2 stroke 20hp mercury 1989,when I run 10-90% throttle it's works fine but when in 100% its only runs in 90% and doesn't sound normal like it's not burning right.

May 11, 2012 | Seloc Mercury Outboard Engine Repair...

1 Answer

Free download for repair manual for an Evinrude 1987 40HP outboard motor

My outboard motor is old and used.When I went to run it for the first time everything worked except when I went to put it in forward gear the boat went slowly but when I gave it more gas the engine just reved up but the boat wasn't going any faster.The motor is 40hp gale model.I think because it is bought used the prop is not the right one and it seems like it's slipping as I go faster.
I would appreciate any feedback on this problem.

Thax, Don

Apr 27, 2011 | Clymer Marine Maintenance and Repair...

1 Answer

I have a 1997 Yamaha 40hp....C40PLRV without oil injection. My Sealoc manual calls for a 100:1 fuel mix. I had a dealer tell me to run 50:1, but it idles rough and is hard starting when cold even with...

Mate.2 stroke motors WITH oil injection run between 100/1 and down to 40/1(rich).With yours being pre-mix,it should run at 50/1 to be safe.Using a good quality 2stroke oil,with low smoke,it should run well.The only thing that may change, is how you use the motor.Slow trolling or running along travelling.A spark plug that is 1 heat range hotter will help burn the fuel/oil mixture if you do a lot of slow running.Faster and /or high speed running,will keep your plugs ok.These are safe guides not to cook up a piston.Hope this helps you

Dec 06, 2010 | Boating

2 Answers

Yamaha 50 hp motor oil red and green oil sensor lights are on

The engine will self destruct if you continue to run it without the proper oil mixture. Some oil systems have to purged of air if ran dry. Seek professional assisstance.

Aug 21, 2009 | Bass Pro Boating

1 Answer

Engine cuts out while running

Sounds like a coil pack getting hot and breaking down

Aug 07, 2009 | Boating

3 Answers

4 stroke Yamaha 50HP -Runs rough at all throttle levels

If it has the old points system you will need to set the points also adjust the carburatior screw the screws all the way in and back out 2 1/2 turns then get it to run turn the air mixture screws till it runs smooth. you want it slightly lean then enrichen it slightly, afterword shut the engine down and look at the plugs if they are gray black they are ok. good luck.

Jul 09, 2009 | RTO Oar Sockets

3 Answers

40hp 1987 yamaha outboard motor will run for 30-60

Sound like the fuel pump is not keeping up with the engine's demand. Check it out. Good luck. Hope this helps.

Apr 27, 2009 | Boating

Not finding what you are looking for?
Sport & Outdoor - Others Logo

Related Topics:

339 people viewed this question

Ask a Question

Usually answered in minutes!

Top Sport & Outdoor - Others Experts


Level 3 Expert

78936 Answers

Bill Eager

Level 3 Expert

433 Answers

Brad Brown

Level 3 Expert

17093 Answers

Are you a Sport and Outdoor - Other Expert? Answer questions, earn points and help others

Answer questions

Manuals & User Guides