1973 Merc 500 Problems

[mbnjagn]

Hi All.

I am at a stand still with where to go next on this issue. What is happening is the motor is dying on hard acceleration from idle. Every once in a while you can get it to work. If you idle around to pick up a skier or tuber then "hit it" she will 80% of the time die out. Then it can be a little tricky to get started at times and other times you just flick the key start and she runs again but will possibly die again on acceleration. I had this problem, then rebuilt the carburetors and the fuel pump and I was still having the problems, so then I then replaced all the fuel lines in the engine, I also took it into the dealer and had then do a "link n sync" thinking that something was not adjusted correctly. I have 10 psi less in the bottom cylinder but it is completely within norms and a top bearing that is making noise and is starting to wear. I just wish I could find out why it is dying on me. I have also tried an external tank and have the same problems.

Does anyone have anymore ideas to try?

Thanks!

 

[Yepblaze]

Re: 1973 Merc 500 Problems

Have you tried squeezing the primer bulb while it does this to see if it's still starving?

What do the spark plugs look like?

 

[mbnjagn]

Re: 1973 Merc 500 Problems

Hi.

Yes we have tried the primer bulb and once and a while it will help, it does not go completely soft.
The spark plugs do not look that bad at all. They were just put in. I know once a couple weeks ago I saw what I thought were tiny little water drops on the plug from the #2 cylinder but now I do not see them anymore.

 

[Yepblaze]

Re: 1973 Merc 500 Problems

Soft or hard, I don't recognize as a diagnostic tool, but if by squeezing (done by copilot) the bulb, the acceleration problem goes away, it's still starving before the carb. Which might be corrected at the fuel pump. I've found that when I do a fuel pump I will usually buy the check valve kit which includes the diaphram(s). It's usually only a few bucks more. It can be a bit challenging getting all the old check valve seat gaskets cleaned out, but very rewarding if it was something that needed attention.


Have you tried unscrewing the idle air mixture screws a little. Although they are mainly for idle, their adjustment can effect the way the motor throttles up.

So I'll assume by your answer that all the spark plugs were running about the same color? That's good, and suggests that you are probably not dealing with just one carb or the other, as if one of the carbs were problematic I would think the pair of plugs it runs may have a distinct different look than the other two.

Any droplets of water may have meaning, but I'll leave that to someone else for insight.