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Mercury 20HP problems - help #13728556 10/12/20 06:09 PM
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I have a 20HP 4 stroke Mercury on my wife’s little pontoon boat. Motor is only 2 years old. It does stay on the water for probably 9 months out of the year. This last weekend the motor would start just fine but when you gave it gas the motor would choke down. It would not die, but it would not power up like it should. The motor is only 2 years old so I am surprised I am having an issue like this.

Could it be an issue with the Fuel Demand Valve or the fuel line? If there is a small leak in the fuel line or primer bulb letting air in, would it cause this type of problem?
Any suggestions would be appreciated.

Thanks


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Re: Mercury 20HP problems - help [Re: TBS] #13728697 10/12/20 07:41 PM
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steve@S2Marine Offline
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check the fuel line first. if you have ethanol fuel and the wrong line, it's likely the inner liner has deteriorated.


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Re: Mercury 20HP problems - help [Re: TBS] #13728766 10/12/20 08:28 PM
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I bought the motor at Bass Pro and they gave me the fuel tank and the fuel line, so it is probably not a Mercury OEM fuel line, probably an Attwood brand.


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Re: Mercury 20HP problems - help [Re: TBS] #13728975 10/12/20 10:49 PM
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1956Zebco Offline
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Just went through this on our 30 (same series 4 stroke Merc.) The high speed fuel pump was bad. Our own fault, we generally just put-put around and you need to run them (rpm) up frequently or they'll seize.

Last edited by 1956Zebco; 10/12/20 10:50 PM.

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Re: Mercury 20HP problems - help [Re: TBS] #13728994 10/12/20 11:06 PM
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Well that’s not what I wanted to hear, but thanks for the information.

Did you change it yourself or have someone do it?

How much did it cost to fix?


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Re: Mercury 20HP problems - help [Re: TBS] #13729246 10/13/20 02:04 AM
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My 115 did that in the Spring and it was the plugs.

I had the fuel lines changed, siphoned all the gas out and put fresh gas in, and had the oil changed etc. but they didn't change the plugs because Yamaha didn't recommend it at the hours on the engine.

I told my wife I was going to try new plugs and when i did it took off like it was supposed to! bolt


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Re: Mercury 20HP problems - help [Re: TBS] #13729362 10/13/20 09:56 AM
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1956Zebco Offline
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Originally Posted by TBS
Well that’s not what I wanted to hear, but thanks for the information.

Did you change it yourself or have someone do it?

How much did it cost to fix?


Didn't do it myself. The hardest part was the part itself, had to wait over a month just to get it in. I had replaced the plugs, fuel filter, fuel lines, on and on (I didn't realize these things had separate pumps for hi and low speed). The pump is on the left side of the engine looking forward, above and forward of the fuel filter, under its own cowling. $300 bucks and change was the cost (part included).

It was a very frustrating problem since we couldn't figure it out. Would run fine at any slow speed, never skip a beat. Give it the gas and it would sputter and eventually die.


Big Bass Deep Diving Spinner: https://youtu.be/nSH_KKAiuB4
Zebco 33 O-Ring Replacement (all years): https://youtu.be/NEU56UGzxXo
Big Bass Toothpick Trick: https://youtu.be/QC0emZqU36M
Crappie Tip: https://youtu.be/27AuG3CEpOs
Zebco 33 Restore & Lube: https://youtu.be/_4BTSEVcbQ4
More: https://www.youtube.com/channel/UCPSsiJFU2JVh-dfIn1jfZDg/
Re: Mercury 20HP problems - help [Re: TBS] #13729457 10/13/20 12:33 PM
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Originally Posted by TBS
I have a 20HP 4 stroke Mercury on my wife’s little pontoon boat. Motor is only 2 years old. It does stay on the water for probably 9 months out of the year. This last weekend the motor would start just fine but when you gave it gas the motor would choke down. It would not die, but it would not power up like it should. The motor is only 2 years old so I am surprised I am having an issue like this.

Could it be an issue with the Fuel Demand Valve or the fuel line? If there is a small leak in the fuel line or primer bulb letting air in, would it cause this type of problem?
Any suggestions would be appreciated.

Thanks


under 30hp 4S engines are made by tohatsu. if you need parts, i'd look into the tohatsu brand parts. easier and faster and probably cheaper to buy.
i'm a tohatsu and mercury dealer. if you need it diagnosed bring it out it to Quitman. i'll be happy to check it out for you.


www.hydrodynamics-usa.com
info@hydrodynamics-usa.com
903-763-5225
www.s2marine.com
s2marinesales@gmail.com
Blazer Boats, Gambler boats and Legend Craft Boats




Re: Mercury 20HP problems - help [Re: steve@S2Marine] #13729477 10/13/20 12:43 PM
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1956Zebco Offline
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Originally Posted by steve@hydrodynamics

under 30hp 4S engines are made by tohatsu. if you need parts, i'd look into the tohatsu brand parts. easier and faster and probably cheaper to buy.
i'm a tohatsu and mercury dealer. if you need it diagnosed bring it out it to Quitman. i'll be happy to check it out for you.


Yes - ours is Tohatsu - so you're the guy that could get the part and have the diagnostic computer to rig it. Good to know. Thanks.


Big Bass Deep Diving Spinner: https://youtu.be/nSH_KKAiuB4
Zebco 33 O-Ring Replacement (all years): https://youtu.be/NEU56UGzxXo
Big Bass Toothpick Trick: https://youtu.be/QC0emZqU36M
Crappie Tip: https://youtu.be/27AuG3CEpOs
Zebco 33 Restore & Lube: https://youtu.be/_4BTSEVcbQ4
More: https://www.youtube.com/channel/UCPSsiJFU2JVh-dfIn1jfZDg/
Re: Mercury 20HP problems - help [Re: 1956Zebco] #13729536 10/13/20 01:28 PM
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Originally Posted by 1956Zebco
Originally Posted by steve@hydrodynamics

under 30hp 4S engines are made by tohatsu. if you need parts, i'd look into the tohatsu brand parts. easier and faster and probably cheaper to buy.
i'm a tohatsu and mercury dealer. if you need it diagnosed bring it out it to Quitman. i'll be happy to check it out for you.


Yes - ours is Tohatsu - so you're the guy that could get the part and have the diagnostic computer to rig it. Good to know. Thanks.


yes.. i have the diagnostic hardware for both engines


www.hydrodynamics-usa.com
info@hydrodynamics-usa.com
903-763-5225
www.s2marine.com
s2marinesales@gmail.com
Blazer Boats, Gambler boats and Legend Craft Boats




Re: Mercury 20HP problems - help [Re: TBS] #13729675 10/13/20 03:14 PM
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Thanks for the input. I think I will start with checking the fuel line and fuel filters and move to the spark plugs before I tackle the fuel pump.


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