'79 20HP thunderbolt bogging badly

[mysouthernwings]

This thing ran like a champ after it was bought last summer. It had a newly rebuilt carb, and new plugs. Slowly, however, it started to surge. It progressed to the point now that it will idle/troll fine, but when you open the throttle it boggs down bad. It is not missing, but it has no power. I have just now gotten back into a schedule that will let me go fishing, and I want to go!! Thanks in advance for your help.

 

[crookedmullet]

Re: '79 20HP thunderbolt bogging badly

Southernwings-<br /><br />Have you checked your gas tank or the gas itself? I have a buddy who spent hundreds of dollars and days not fishing only to find out that his gas tank had a leak which allowed water to get in. Check the fuel and let me know what happened.<br /><br />crookedmullet

 

[mysouthernwings]

Re: '79 20HP thunderbolt bogging badly

thanks crookedmullet, I will try that. I have changed the line, and bulb, but not the tank. I will keep you posted.

 

[Daquet]

Re: '79 20HP thunderbolt bogging badly

I have this same Problem, I replaced the Hose and even took it in and got a tune up, I will Change the gas tomarrow and check it out, LMK if this worked for you mysouthernwings

 

[Daquet]

Re: '79 20HP thunderbolt bogging badly

Well it didnt help Ran ok cut out only 3 times the first 20 minuts then I couldnt get it started<br /> After choking it a few times it started ok but ran worse, boged down made kinda like a chattering sound

 

[Ginder75]

Re: '79 20HP thunderbolt bogging badly

I have a 1977 Mercury 20hp that did something similar. It had a rough idle, sounded like the motor was going to shake it self apart. And when under power it would bogg down and run at half speed. This condition would come and go, what I eventually found was that the switchbox had corroded wires and the insulation had started falling off the wires. I was able to repair the wires at the lake and save a weekend, but I am saving the cash for a new swithcbox from Mercury.<br /><br />When the problem first presented itself, I thought and was told to check the carb. When that did not produce and results, I started checking the wires. When it broke in my hand I knew I found the source of at least some of my problems. Fixed it and readjusted my carb, now it runs like a champ.<br /><br />By the way, when I started checking the motor at home on the muffs I could not make it act the same. I had to be on the water with the boat in gear to get enough resistance to really make the problem obvious.