1975 Mercury 1500

[Jhenry72]

Hello, I am fairly new to the boating world and recently purchased a "New to Me" boat with a 1975 Mercury 1500 "Tower of Power"! The seller stated that the engine needed a new Internal wiring harness, which I purchased and installed. Long story short, I finally got the engine to fire and seems to run good on the muffs. Problem I have is when I take it out on the water, I put it in gear, start to give it more throttle, and It pukes out and dies... Most of the time it starts right back up but I haven't been able to get it to go! It has no problem revving up in neutral, but as soon as I put it in gear and give it gas it dies. I have read posts that suggest doing a "Link and Sync" and also setting the Idle Mixture screws. I should note that it doesn't usually die right away when I put it in gear. Because I have been able to at least get past the No Wake buoy. Any advice is Greatly Appreciated! John.

 

[Chris1956]

Re: 1975 Mercury 1500

sounds like diry carbs or mis-adjusted idle mixture. Richen the idle mixture one carb at a time, and see if she will accelerate better.

if you have a timing light, put it on the top spark plug and remove the othe plugs and ground them. While cranking motor adjust throttle until you see 4-6* BTDC. At that moment carb should just be ready to open. Max timing is 21* BTDC. If it is off, get an OEM service manual and do the link and synch.

 

[Jhenry72]

Re: 1975 Mercury 1500

Thank you Chris1956! I will try that this weekend. I bought a Seloc Manual that has been Really helpful also! Thanks Again!

 

[hotrod53]

Re: 1975 Mercury 1500

You may not be running on all carbs. An outboard will idle seemingly OK with a dead carb, but will have no power. This being a new to you motor, you may not hear the difference. I suggest that you pull the carbs. you may have a stuck needle valve that caused a carb to go dry. This has happened to me multiple times on my 4 cylinder Merc 500. Ethanon in the fuel will swell the rubber tipped needles and cause them to stick in the seat if you don't run a little fuel out if the carbs at the end of the day. This allows the floats to do down and pulls the needle out of the seat while it sits.

 

[Jhenry72]

Re: 1975 Mercury 1500

Thank You for the information on the Carbs! I will definitely check them out! Although I was told by the previous owner that all 3 carbs were rebuilt 2 years ago. Could this still be an issue? Also, I have noticed that when I pump the ball too much at times, gas drips from the carbs. I have reset the idle mixture screws this passed weekend. All 3 screws were only unseated about a turn out! I set them 1 and 3/4 turns out each and Engine did Start right away and Run Way better! Just waiting for the weather to cooperate so I can take it to the Lake!
Thanks Again for all the information! Much Appreciated!!

 

[wired247]

Re: 1975 Mercury 1500

Those motors run on a pound or two of fuel pressure. Pump the bulb hard and you are pretty much guaranteed to push gas past the needle and seat. Its not really a problem unless the float level actually is set wrong.

Those carbs are pretty crude with no off idle transition circuit. The idle screws fatten up the mixture and make the idle to high speed transition somewhat smooth.

 

[hotrod53]

Re: 1975 Mercury 1500

rebuilt 2 years ago or 2 days ago makes no difference when yoiu throw ethanol in the mix. I have quite literally run my motor yesterday and had a needle stuck today if I don't run the bowls down when I'm done for the day.

And yes, you can easily force fuel past the needle when pressurizing and the float level is so high it doesn't take much to run it over.