Older Merc 500 - no power

[along]

I'm resurecting my old early 70s boat and 500merc. I havent run it in almost 7 years and i'm sure I didnt drain the gas or put conditioner in it when we parked it.
I put in new leg oil, new plugs etc and it fired right up. Sounded normal so we took it to the lake to give it a run. I hit the throttle and got nice power out of it and got it to top speed then... no power. I think it's maybe got 1/3 of normal power now so we just trolled for trout all afternoon as it idles real nice.
Question: is there a fuel filter in the motor? I'm thinking there's some old crud somewhere. Maybe carbs should be taken off and cleaned out?
Anyway, if you have any ideas, thanks in advance.
Al

 

[WillyBWright]

Re: Older Merc 500 - no power

If they sat with gas in them, don't even wonder if they need cleaning. They do! I see varnishing over a single winter with motors that haven't been winteized. But after 7 years, even treated gas will have varnished.

 

[tashasdaddy]

Re: Older Merc 500 - no power

you need to do several things before you blow it up. complete carb soaking and rebuild, you also need to service the water pump, and replace the impeller, it's a wonder it didn't go out on this trip. if the impeller comes apart while running it can send bits into the cooling system and clog ports, and is a ***** to clear.