85 mariner 20 no power until heated up

[gillgetter]

My 85 Mariner 20 hp will start up first or second pull. Idles ok. But when I leave the dock it has no power. I hold it wide open and it runs without missing or sputtering but sounds bogged down with very low speed. I hold it open for about 5 minutes until it gets warm and it lunges a couple times, then it takes off and runs great with full power. I run it fast for a while until its warmed up good, and for the rest of the day I can start and stop for fishing and even if it cools down for an hour, it starts and runs great. The first time it did this was my first time out for the year, so I thought old gas. Ran that tank almost dry, then put in new non ethenol gas and seafoam. Same thing next time out. Put new spark plugs in. Same thing next time out. What could cause it to start good and run with no power until hot? Thanks

 

[tommarvin]

Good for you to use non ethenol gas were to cheap, its 80 cents a gallon more where we live.with seafoam, its a great product we use it to decarb at the end of the season,did it two boating trips ago.
You want to use stabil 360 marine with vapor technology at every fill up, wait a minute does it help with non ethenol gas IDK.
Anyway your carbs are dirty,remove them and clean them like all the you tube videos please.
New on motor fuel filter, install a fuel water seperator if you want less boating/fuel problems.
Its amazinig that new spark plugs NEVER fix anything oh well.

 

[flyingscott]

Check for spark when that happens. Have you checked your compression? There is no mechanic in a can! Does your motor have a thermostat housing or not?

 

[racerone]

Perhaps run with a timing light hooked up.-----You might find that one cylinder is not sparking when cold.------If that is what you find then switch coils and see if fault goes along with it.

 

[gillgetter]

Thanks for all the feedback Great website! I don't have a compression tester or inline spark tester here at my cabin to make those checks. Next time I come back I will bring those and my water muffs so I can run it on a hose. I don't know how to run a timing light so that is above my level of expertise. I just put a new fuel filter on it this year. Carbs have never been cleaned since new so I will start doing some youtube research on that. I don't know if it has a thermostat or not. I will check that now. I do have a good force water discharge right from start up. Now the coil. This is what I was thinking. Can it cause a motor to run on one cylinder until warm, then kick in and run great the rest of the day? Sits for a week, then repeats. Any way to check the coil without a timing light? Would there be a weak or no spark on one cylinder if I pulled the rope when motor is cold? Thanks

 

[Sea Rider]

For such an oldie OB, seems it's a temp related issue. Remove thermostat, probably it's stuck open, rusted, salted if engine is used on salt water. Thermo it's not doing its homework right. Install a new one along gasket. Anyway, any engine needs to be warmed up for at least 3 to 5 minutes before applying more throttle passing idle.

Personally would install a new head gasket, thermo and clean all water powerhead's paths.

Happy Boating

 

[gillgetter]

I did not even know it had a thermostat until I just looked at it. Seems like an easy fix if that's my problem.I have owned this motor since new. I have always fired it up and ran it hard without to much warm up. This problem is new this year. I am going to order a new thermostat and gasket now. Cheap fix if that's it. Wouldn't I see a leak around my head gasket if that was a problem? I thought if it had a strong water discharge, everything was good for the cooling system. Impeller was changed last year. Thanks

 

[flyingscott]

Do you have a yamaha or.mercury built motor?

 

[Sea Rider]

Is that baby used in fresh or salt water, has low, medium or high hours used ? To get the idea, Nobody retorques their head gasket after break end period has ended, and that's factory mandatory. Salt will make its way around gasket and screw it in the long run. Remove thermo and check its condition...

Happy Boating

 

[Faztbullet]

Nobody retorques their head gasket after break end period has ended, and that's factory mandatory. Salt will make its way around gasket and screw it in the long run. Remove thermo and check its condition...​

Sea need to learn your motors....The only Mercury built 2 stroke motors with head gaskets are V-6's..every thing from a 2hp to 140hp are jug style motors. Gillgetter test trigger but bet putting a CDI box on it will fix it.

 

[gillgetter]

I believe this motor was made by Yamaha. Never have run it in salt water. I only use this boat 5 to 10 times a year for fishing. Usually run it wide open to get around. Ran it yesterday and it did the same thing. I let it idle for a few minutes before I opened it up. It started to run good then bogged down for about 4 minutes before running great. No problems the rest of the day. What exactly is a trigger and how do I check it? Thanks

 

[gillgetter]

I just watched a video on you tube about the trigger. Looks like the stator I replaced on my pontoon 40 hp.with a lot less wires. I had a mechanic friend help me with that. I am still going to change the thermostat out and clean the carb. If that doesn't work I guess I will call in a pro. CDI looks expensive to just change without knowing if its bad. Thanks for all the input from everyone. It gave me a lot of ideas where to start looking.

 

[Faztbullet]

Post a picture of motor...also if a yammi built it may have points!!!!