Issue with the carbs?

[kembry]

History:

I have a 1974 500 50hp Mercury that was given to me Spring of 06'. Summer of 06' I replace fuel lines, bulb, diaphram and checks valves in fuel pump. I also took the carbs off, cleaned them and put a new kit in each and followed my seloc manual exactly on the adjustments. I hooked it up to fresh fuel and got it running pretty good off of a hose. Took it to the lake for a test.

Results:

To get her in gear without dying I had to keep the idle speed up a bit. Once in gear she would stand the boat up and here we go but just before it would plane out it would die. A few pumps of the bulb and she fires right up but has the same problem. I had a buddy with me that would pump the bulb as it was loosing power but that didn't help. For the rest of the summer I continued to work on it without any better results.

June 07' I decide to take it to a mechanic. For 13 months it set at his shop without any attention. I went to check on it 3 days ago and to my suprise he was working on it. He had flushed the carbs and adjusted the linkage between the two. Sounded great on the hose. Yesterday I put it on the water for another test.

Results:
Motor starts much easier, probably due to a brand new battery. Goes in gear forward and reverse at normal idle speed. Once in gear, I'm going what I would call a "no wake zone" speed just fine but as I advance the throttle to pick up speed, it dies. 95% of the time I don't have to pump the bulb to get it started back up. The only way I am able to advance past this speed is, while I try to advance past this speed, choke it pretty good and then I can go. Once I move past the "no wake zone" speed it sounds like she could run all day at whatever speed I choose. I slowed her back down, went to nuetral, then back in gear and it dies again. I then try my new trick with the choke, sometimes it works, but most of the time is does not. My mechanic came down the hill to check on me, got in the boat and had the same problems, he played with the idle mixture screws a little and the motor started sounding better, but still has the same problem. His recommendation was to "run the hell out of it, it probably needs more time in the water, maybe ten hours worth, and we'll see what happens".

Sorry this post is so long, but I wanted to be very thorough. Going on year three and I'm itching pretty bad!

Any and all help is greatly appreciated.

 

[kembry]

Re: Issue with the carbs?

Yesterday I put it back on the water. The motor cranked up on the first try. I eased her through the no wake zone and out into the lake. As I tried to advance the throttle she started to bog a little so I hit the choke and off we went. For 25 - 30 minutes I ran her from between half to full throttle. During this time it would surge and sputter a little. At the 30 minute mark I was going full throttle when all of a sudden she bogged down and died. After this I was able to get it started but would die each time I put it in gear. Is it possible that the idle mixture screws can move when a motor is vibrating a little when it would surge?

After the thirty minute ride I pulled the plug wires off. Plug #1 and #2 were very hot to the touch and plug #3 was only warm. I couldn't reach #4.

I also broke the shift cable or stripped something in the controls.

Just when things were looking up, it's taken a turn for the worse.

Thanks

 

[BR]

Re: Issue with the carbs?

Sounds like a carb mixture adjustment to me. If you had the carbs off to clean and rebuild you should probably also do a link and sync procedure. An excellent "step by step" for Mercury inline motors can be found on this forum under Engine FAQ?s. Follow this link: http://forums.iboats.com/showthread.php?t=168855.

The fact that your #1 & #2 plugs were very hot plus the fact that choking seems to help get her back may indicate that (at least) your upper carb mixture is too lean. Try the default setting for mixture: turn adjustment screws in just until lightly seating the needles, then back out 1 1/2 turns. Do this for both carbs and observe any changes. Adjust mixture in 1/8 turn increments and do both carbs together. I do this while idling in gear in the water (puts a load on the motor but also requires two people). You know you are close to correct mixture when you get an acceptably smooth idle and can punch it to wide open throttle (hole shot) without bogging or dying. Good luck and don't give up!

 

[kembry]

Re: Issue with the carbs?

BR,

Thanks for the reply. Once I get the controls fixed I'll start back on the motor. I did find a very small diameter tube/hose, that goes from the bottom of the motor to the top on the same side as the fuel pump, that had come off or been replaced at some point. The bottom connection has a nut and the top has a hole that it fits in. Someone must have put it back in the hole at the top and used JB weld? to get it to stick. It was very loose and may be allowing air to enter. Is this some type of overflow tube? I can't find it anywhere in the manual?

 

[BR]

Re: Issue with the carbs?

Kembry,
I think the hoses you are seeing are lines which allow fuel/oil mixture to be pumped from the crankcase to the top and center main bearings. These lines have check valves which should only allow fuel/oil mix to move up and away from the crankcase.