1979 Mercury 500 Thunderbolt 50HP losing fuel pressure

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Hello,
I'm pretty new to outboard motors, and am having fuel pressure issues with my 79 Merc Thunderbolt 500. I had it out and it started to lose power and wanted to stall out. I checked the ball on the fuel tank and it had no pressure. It will run fine if I periodically prime the ball, but it eventually loses pressure and dies. I assumed it was probably the fuel pump. After further inspection and tinkering I dont think it has a fuel pump? I've traced the fuel lines out and it just seems to run from the tank to the carbs. I'm not sure if I'm missing something or this model doesnt have a pump and just operates under some vacuum pressure. I'm also having issues finding any info on my model number. This motor has coils for each cyclinder, I've seen several like mine that are distributed that have a fuel pump visible (not sure if that helps with identifying this particular motor). Any ideas or suggestions would be much appreciated.

 

[racerone]

No, no it has a fuel pump and possibly 2 of them built into the carburetors !!---------Test run with another tank and hose.-------And no the bulb does NOT stay hard once the motor is running !

 

[rustamas.boikulovas@gmail]

Hello,
I'm pretty new to outboard motors, and am having fuel pressure issues with my 79 Merc Thunderbolt 500. I had it out and it started to lose power and wanted to stall out. I checked the ball on the fuel tank and it had no pressure. It will run fine if I periodically prime the ball, but it eventually loses pressure and dies. I assumed it was probably the fuel pump. After further inspection and tinkering I dont think it has a fuel pump? I've traced the fuel lines out and it just seems to run from the tank to the carbs. I'm not sure if I'm missing something or this model doesnt have a pump and just operates under some vacuum pressure. I'm also having issues finding any

No, no it has a fuel pump and possibly 2 of them built into the carburetors !!---------Test run with another tank and hose.-------And no the bulb does NOT stay hard once the motor is running !

info on my model number. This motor has coils for each cyclinder, I've seen several like mine that are distributed that have a fuel pump visible (not sure if that helps with identifying this particular motor). Any ideas or suggestions would be much appreciated.

Hi I have same problem. How you sort it out? Many thanks!

 

[oldsoul]

Hi I have same problem. How you sort it out? Many thanks!

I recently had the same issue with my 1977 thunderbolt 850. Rebuilt the carbs, rebuilt the pump. Still not fixed. Replaced the fuel lines and primer bulb, and done! I had that crappy hey fuel line and the inner liner separated causing the line to be restricted, additionally, some of said liner separated and jammed the check valve in the primer(that's how I figured it out). Never, never, never will I use that crap again.

Lesson learned: start with the simple stuff first.

 

[ocboat]

I recently had the same issue with my 1977 thunderbolt 850. Rebuilt the carbs, rebuilt the pump. Still not fixed. Replaced the fuel lines and primer bulb, and done! I had that crappy hey fuel line and the inner liner separated causing the line to be restricted, additionally, some of said liner separated and jammed the check valve in the primer(that's how I figured it out). Never, never, never will I use that crap again.

Lesson learned: start with the simple stuff first.

I couldn't agree more. I had multiple issues and thought that I had done everything that I could to solve my fuel problems but it wasn't until I replaced the little 2 inches of hose that connected my carbs together that I solved my issue. My advice would be to change out every fuel line from tank to carbs.