'76 Mercury 500 50 hp

[jasonhuber]

I recently purchase a 16' thundercraft which has a '76 50 HP merc 500. It runs fairley well, but has an issue to which I havent a clue as how to fix.<br /><br />When I run at lower RPm it runs great and picks up until about 1/4 throttle and begins to die. If I pull it back to idle and gun it, it goes, but I cannot nurse it up to full throttle. <br /><br />If I am at Full and bring it back, I can go down pretty far, but not to idle.I have to kick it back pretty far quick and then back up to keep it going. <br /><br />It will go from 0 to full or from 0 to 1/4 but not from 1/4 to 1/2 and up.<br /><br />I checked the plugs they were in good shape, it seemed to get worse when I added 91 octane fuel, but I havent a clue what to check.<br /><br />I have a repair manual, but the descriptions arent great and it leaves me wondering if this is something I can test out of water with the hose hooked up or not?<br /><br />Here are my questions:<br />1. Can I test the engine with the hose hooked up at full or near full throttle? (out of water - with hose)<br />2. Which screw should I be adjusting?<br />3. Anything else I should check first.<br /><br />I can take it to the lake like this, but everyonce and a while I cannot get it up to full throttle. It will just die over and over again. I have to bring it to idle and then gun it like 10 times before it will take off.

 

[Chinewalker]

Re: '76 Mercury 500 50 hp

Sounds to my like you've got a "floater" or three in the carbs. When you slosh the carbs around during acceleration the bit of grit gets nestled up to the gets and boggs it down. To slow down and the draw is lessened, it falls away and maybe this time you accelerate just fine.<br /><br />I would remove and disassemble the carbs, clean everything out with carb cleaner, paperclips, compressed air, whatever it takes to clean out the jets and passages.<br /><br />Also, couple of quick things to check - is the fuel tank properly vented? Anything in the boat sitting on the fuel line?<br /><br />Don't bother with the 91-octane - your motor is quite happy with mid-grade 87 or 89 properly mixed with TCW-3 rated oil of your preference.<br /><br />- Scott

 

[jasonhuber]

Re: '76 Mercury 500 50 hp

OK I guess something did come to mind- the tanks have a filter in them and I guess I assume that these could be clogged as well. I may also buy new fuel lines.<br /><br />I still think there is something in the timing or distributor at fault since it will idle up pretty fast but die about 1/2 way or less.<br /><br />Can I run this engine with the hose hooked up at full throttle with no damage? Even for seconds?

 

[rickdb1boat]

Re: '76 Mercury 500 50 hp

no!