# Rough idle during Low RPM



## Tarponfisher92 (Jul 23, 2017)

I have a 1998 15hp Mercury 4 stroke with an unknown amount of hours. The motor runs very well in high rpms; however during low rpms like in minimal wake zones it runs very rough. Any ideas what this might be from. Motor has great compression in each cylinder.


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## yobata (Jul 14, 2015)

Does a 4 stroke motor have air mix screw(s) like 2 strokes? I guess prob not since there's no carbs. Anyway, that helped my motor run better at idle rpms


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## Tarponfisher92 (Jul 23, 2017)

yobata said:


> Does a 4 stroke motor have air mix screw(s) like 2 strokes? I guess prob not since there's no carbs. Anyway, that helped my motor run better at idle rpms


I wouldn’t think so but I can look


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## MooreMiller (Sep 10, 2016)

yobata said:


> Does a 4 stroke motor have air mix screw(s) like 2 strokes? I guess prob not since there's no carbs. Anyway, that helped my motor run better at idle rpms


Most 4 strokes that I've worked on had air mix screws.


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## Steve_Mevers (Feb 8, 2013)

My friends fuel system was dirty and we disconnected the fuel line and injected engine tuner while cranking it, let it sit for awhile and then cranked it up and it cleaned the fuel system and it ran perfect. We have been doing this for years on everything from chainsaws, ATV's, to 2 stroke engines. https://www.amazon.com/Johnson-Evin...d=1508068867&sr=8-1&keywords=omc+engine+tuner


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## JET4 (Jul 14, 2014)

I had the same problem with Tohatsu 9.9 outboard. I got a bottle of Amsoil Quickshot and ran it through the motor. Motor runs like brand new now. 
https://www.amsoil.com/shop/by-product/fuel-additives/gasoline/quickshot/?code=AQSCN-EA


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## Tarponfisher92 (Jul 23, 2017)

JET4 said:


> I had the same problem with Tohatsu 9.9 outboard. I got a bottle of Amsoil Quickshot and ran it through the motor. Motor runs like brand new now.
> https://www.amsoil.com/shop/by-product/fuel-additives/gasoline/quickshot/?code=AQSCN-EA


I’ll give the quickshot method a try first then I dive into it a little bit more if that doesn’t do anything.


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## Whiskey Angler (Mar 20, 2015)

You can also disconnect your fuel line from your tank, and run the engine on a super concentrated mix of gas and seafoam. Then, replace plugs, and try her out.

Read the first post for instructions.

http://forums.floridasportsman.com/archive/index.php/t-625.html


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