1985 mercury 50 hp classic fuel problem

fisherman81654

Petty Officer 2nd Class
Joined
Sep 5, 2011
Messages
135
My friend just bought this engine,we checked compression and all four were 120 psi,new plugs,great blue spark and gas up to the strainer or filter.
We gave it a test run and it ran great until after three quarter throttle then it bogged down.
Back off the throttle ,ran fine.When we got back to the dock later turned it off and went to start it again,nothing,just cranked over.Took out the plugs after trying to start with choke on and found that the plugs were dry and still getting great spark.

Getting fuel through the fuel lines all the way to the carbs,but for some reason fuel is not making it to the plugs.


I thought maybe at first when the motor was running but would not take full throttle the problem may be the fuel pump on side of the carb,but now we are not getting any fuel to the plugs.
Could both fuel pumps have failed?

squeezing the bulb while cranking does not help either.

The serial number is A 949314

Thanks so much in adavance for answers....
 
Last edited:

fisherman81654

Petty Officer 2nd Class
Joined
Sep 5, 2011
Messages
135
Re: 1985 mercury 50 hp classic fuel problem

This motor does have a fuel pump on the side of each carburetor? ( two carburetors, two fuel pumps) correct ? :confused:
 
Last edited:

James R

Commander
Joined
Feb 1, 2007
Messages
2,660
Re: 1985 mercury 50 hp classic fuel problem

Two stroke Motors need the carbs stripping and cleaning and carefully rebuilding with new kits on a regular basis. If this is not done then there is no lubrication to the motor and failure will result. If the carbs have not been serviced recently then they should be done. This is the most likely cause of your problem.
 

quicktach

Petty Officer 1st Class
Joined
Aug 24, 2012
Messages
394
Re: 1985 mercury 50 hp classic fuel problem

I'd pull the carbs and service them. Check linkages after reinstalling to make sure all's in sync.
 

fisherman81654

Petty Officer 2nd Class
Joined
Sep 5, 2011
Messages
135
Re: 1985 mercury 50 hp classic fuel problem

I agree with both of you but he did not do that.
He did tear it down and carbs apart and found that the float neddle valve was stuck on both carb,he cleaned it some and put it back together and it started fine and ran fine till full throttle was applied then it did the same thing ,bogged down,eased off the throttle some ,ran fine.
He did add some sea foam hoping that would clear up any remaining obstructions.

My question is do you know what part of the carbs is causing this to do this and could it hurt the motor as far as maybe its not getting fuel to a cylinder,I dont know if thats the case.

Personaly,I would have went with a total rebuild of the carbs.
 

James R

Commander
Joined
Feb 1, 2007
Messages
2,660
Re: 1985 mercury 50 hp classic fuel problem

You cannot only partially clean and rebuild. Do a proper job or burn up the motor.
 

alfa

Seaman Apprentice
Joined
May 11, 2011
Messages
30
Re: 1985 mercury 50 hp classic fuel problem

If the carbs are not properly cleaned AND adjusted, they'll be able to provide enough fuel to the motor, especially on high demand situations at full throttle or upper rpms. Once you ease on the throttle the carb can keep up... however, is it's been mentioned by others you're walking a fine line with half *** carbs because that's where the lubrication to your motor comes from. You keep pushing it on bad fuel flow (hence oil flow) and you'll have a powerhead to rebuild or replace.

Get a carb kit and the service manual and follow the steps.
Best of luck
 

fisherman81654

Petty Officer 2nd Class
Joined
Sep 5, 2011
Messages
135
Re: 1985 mercury 50 hp classic fuel problem

If the carbs are not properly cleaned AND adjusted, they'll be able to provide enough fuel to the motor, especially on high demand situations at full throttle or upper rpms. Once you ease on the throttle the carb can keep up... however, is it's been mentioned by others you're walking a fine line with half *** carbs because that's where the lubrication to your motor comes from. You keep pushing it on bad fuel flow (hence oil flow) and you'll have a powerhead to rebuild or replace.

Get a carb kit and the service manual and follow the steps.


I completly agree,but its not my motor.Its my neighbors motor.
My question is what part of the carburetor is malfunctioning that causes the motor to boog down only at full throttle.
We have sprayed fuel in the carburetors when full throttle is applied,it makes it worse .That tells me that it must be getting enough fuel at that point.We have not touched the idle screws.

Thanks so much for the replies..
 

mixerjv

Petty Officer 3rd Class
Joined
Oct 28, 2005
Messages
86
Re: 1985 mercury 50 hp classic fuel problem

I have the exact same engine.

By chance, are you using a newer fuel tank? I had the same symptoms and it turned out to be the newer EPA 2012+ non venting fuel tank that was starving the engine.
 

fisherman81654

Petty Officer 2nd Class
Joined
Sep 5, 2011
Messages
135
Re: 1985 mercury 50 hp classic fuel problem

I have the exact same engine.

By chance, are you using a newer fuel tank? I had the same symptoms and it turned out to be the newer EPA 2012+ non venting fuel tank that was starving the engine.

No,but a good point tho.I'll have to get on the back off the boat while hes giving full throttle and loosen the fuel cap.
Maybe it is a problem like that. When we get a chance to do that I'll post results. thanks...
 

FloridaMan84

Cadet
Joined
Nov 20, 2013
Messages
9
Re: 1985 mercury 50 hp classic fuel problem

My friend just bought this engine,we checked compression and all four were 120 psi,new plugs,great blue spark and gas up to the strainer or filter.
We gave it a test run and it ran great until after three quarter throttle then it bogged down.
Back off the throttle ,ran fine.When we got back to the dock later turned it off and went to start it again,nothing,just cranked over.Took out the plugs after trying to start with choke on and found that the plugs were dry and still getting great spark.

Getting fuel through the fuel lines all the way to the carbs,but for some reason fuel is not making it to the plugs.


I thought maybe at first when the motor was running but would not take full throttle the problem may be the fuel pump on side of the carb,but now we are not getting any fuel to the plugs.
Could both fuel pumps have failed?

squeezing the bulb while cranking does not help either.

The serial number is A 949314

Thanks so much in adavance for answers....

I know this sounds stupid but I have the same engine and found out that when going full throttle the parts that move inside the motor pinches off a fuel line starving the motor. I shifted the line out of the way and had no problems since.
 

fisherman81654

Petty Officer 2nd Class
Joined
Sep 5, 2011
Messages
135
I know its been over three years,but today we pulled the lower unit to change the water pump and also checked the exhaust tube.It was almost completely block by many years of carbon build up.We cleaned it out with a pipe.The problem is solved. It takes full throttle now and runs great.
 
Top