Need Help With a 1976 Mercury 500 Thunderbolt 50hp OB....

[Bloodybrim36]

Ok so on the hose this thing feels like it screams to full throttle. When I get it in the water it took off once and went full speed. Then it just kept bogging down when I tried to go full throttle. I changed the spark plugs and it really didnt do much. The motor runs great at idle nice and smooth. However when I give it the juice it just wants to creep on the water but on rare occassions it will "kick in to gear" and take off. Whats the deal here?

Also...really dumb question but how many carbs are supposed to be on this motor? I know absolutely nothing about outboard motors...I can talk a Chevy 350 all day but not these things

 

[MacDaddy21]

Re: Need Help With a 1976 Mercury 500 Thunderbolt 50hp OB....

what is your serial number?

 

[Bloodybrim36]

Re: Need Help With a 1976 Mercury 500 Thunderbolt 50hp OB....

I believe it is 4403255.

 

[MacDaddy21]

Re: Need Help With a 1976 Mercury 500 Thunderbolt 50hp OB....

One thing I want to say before adding anything else, you should not run the motor at any rpm above idle while on the muffs. That is
very hard on a motor and can cause some serious damage.

Now, it should have 2 carburetors. If your motor is bogging when you are trying to go to WOT, it is likely the carburetors or the fuel
pump. Fuel delivery is generally the cause of bogging under load. If you can locate your fuel pump, you can pull the hose off that lead
to the carburetors, and squeeze the primer bulb. If a strong stream of fuel squirts out, the fuel pump is probably okay. The next thing to look into is carburetors. Rebuilding both the carbs is probably necessary if it hasn't been done in awhile. You need to invest in a manual if you have limited outboard knowledge. You should get new gaskets, new floats, and new needle/seats for each carb. If the carbs are especially dirty looking, you can soak them in some chem-dip or chem tool, after removing all the plastic parts and completely disassembling each carb.

 

[Bloodybrim36]

Re: Need Help With a 1976 Mercury 500 Thunderbolt 50hp OB....

There is definitely only one carb on there. Should be one on top and another on the bottom correct?

 

[MacDaddy21]

Re: Need Help With a 1976 Mercury 500 Thunderbolt 50hp OB....

I'm 99% sure it should have 2 carbs. If you can see a mounting location for a second carb, there should definitely be one there.

 

[Bloodybrim36]

Re: Need Help With a 1976 Mercury 500 Thunderbolt 50hp OB....

Yup there is a mount on the bottom end. Why would someone only have one carb on there? Its been changed to that. I just got this thing and obviously got hosed so I dont know anything about what has been done to it.

 

[CharlieB]

Re: Need Help With a 1976 Mercury 500 Thunderbolt 50hp OB....

Verify fuel pump output by cranking the motor with the carb fuel hose disconnected and pointed into a suitable container. You should have a strong pulsed stream at least an inch out and the diameter of the hose.

A lean idle mixture either from maladjustment or a dirty carb will reduce acceleration, causing the motor to bog, hesitate, lean cough, or die.

Idle mixture must be set ON the water while IN Forward gear to best idle speed PLUS almost another 1/8 turn out (CCW) to provide the additional fuel necessary for crisp acceleration.

Once set, test acceleration, any hesitation in the slightest, further richen the idle mixture turn out just the width of the screwdriver blade slot, then retest acceleration. Repeat to perfection.

 

[MacDaddy21]

Re: Need Help With a 1976 Mercury 500 Thunderbolt 50hp OB....

People will do ridiculous things to motors. I found 2 copper BB's crammed in the equalizer tube on my carburetor. You'll need to get
another carb, and make sure all the linkages are there so the 2 carbs can be linked up properly to work in conjunction.