Motor wont start when warm

[RMasters]

Folks, I have a phenomenon which needs to be solved, I have done everything that can be done (including common sense and a Mercury mechanic).

Our motor (1964 Mercury 850) is good. Full compression, yearly inspected, cleaned, lubed etc. (spring and fall) and all parts are up to date (new fuel filter, rectifier, spark plugs (6!) etc.).

Motor ran fine on Memorial Day. Always fires right up, with choke when cold, without when warm. But after that weekend, once warm, it wont start anymore! I used all the tricks you hear about (the motor never needed any), and even ran down my 1000 amp battery. Luckily I have a 900 amp jump starter on board, besides that I don't want to get towed, the embarrassment is just too much.

A spray of starting fluid helped, it fired right up, I mean right away. But then again, after half an hour or so, it does it again.

Took it to shop, they checked everything, all is fine.

Now, the only thing different that I noticed is that, when driving at idle speed for about 15 minutes, I smell gas and the motor starts running rough. When I open the throttle then to accelerate (moderate!), it eventually settles, motor runs smooth then and no fumes.

Someone suggested that it could be debris in either the (carburetor) jets or the diaphragm. Should I have the mechanic pull out and clean all these parts? Do you think that some SeaFoam spray in the carburetors would help, or be worth a try (vs. getting the trailer and towing for 1 hour).

Besides mechanically in top shape, so are what I use on the engine. Unleaded gas, Mercury Fuel stabilizer and Fuel System cleaner, Mercury oil, so I take it this is not an issue.

Any input would be greatly appreciated! Am out of ideas, not even mechanic knows what to do.

 

[Chris1956]

Re: Motor wont start when warm

Do you see lots of gas/oil on the water when cranking? if so, it could be fuel pump diaghram. Once you get it started it runs OK, or does it load up at idle and struggle to acelerate?

 

[Rubixone]

Re: Motor wont start when warm

just a quick add it sounds like a carb issue, drain n clean the bowl to make sure no dirt is keeping the float from closing, also when the coil packs get warm and expand if they are cracked your spark will ark out and not fire, same with any bad plug wires, check for cracks, if when it is warm and it looses spark check that. if the spark is good pull carb, soak it overnight in cleaner, dont soak any plastic parts though as it will eat it. grab a carbkit for 30 bucks and replace the parts, a bad float or stuck needle will flood out the carb cause fuel just keeps pouring in.

 

[RMasters]

Re: Motor wont start when warm

Thanks for all the input.

There is no gas/oil in the water nor engine compartment, it is pretty much dry. No smell either. Fuel pump and diaghram are new (which does not mean they could go bad, but they were checked and considered fine).

Once the motor starts, it runs perfect. Except what I described before, that when running slow for quite some time, it appears to load up.

Looks like cleaning the carbs and jets would be the task to do I guess. I got some SeaFoam spray and give that a try, maybe it will help or even solve, but I would not completely trust it. Probably have to get it out of the water and the carbs/jets cleaned.

Thank you all for your input. Looks like my marina is charging less than $100 for this job (the motor has 3 carburetors).

Ahoy!

 

[michaud500]

Re: Motor wont start when warm

I have the exact issue!! I have a 1969 500 with two carbs and rebuilt the whole fuel system from tank to carb. I tip the motor and fuel runs out. I have noticed when for the second time of rebuilding,that the a needle for the needle valve would stick in the inlet hole. The needle valve (I have one with a plastic or rubber tip and one without) with the plastic tip would stick a little bit. The one that is all metal would not! I am starting to believe that It is the needle valve sticking and blocking fuel flow!

The only difference that I have is that mine does it either WOT or just tooling around. But it sounds like it is just winding down than wont start.

 

[RMasters]

Re: Motor wont start when warm

Interesting.

Well, I was ready to get the boat out of the water yesterday and to the Marina to check and clean all that. Guess what, it runs only on a few cylinders, I can barely keep it running (idle lever fully up). Could not get it out of the dock to the boat lunch.

Tried to find someone who can give me a tow. Yeah right, there were only 2 boat and I gave both of them the official signal for help. Do I have to say more?

Am not crazy about paddling the boat to the lunch, it is probably only a thousand feet or so away, but I have to go around other docks, and with the waves sometimes coming in (as most dumb boaters wont stay away or slow down). Besides, the boat is a runabout and it is hard to reach out to paddle. And I have to go by a swimming beach. Just too many "obstacles" around.

Wifey suggested to go tonight, late. But she does not want to go (not feeling good right now). Checked with a local Marina, they want $80 for a tow. For a not even 5 minute ride? Geee.

On top of that, Marina called last night and told me that they want me to move to another dock. Great! How?

Hope I find someone to give me a hand today (am making some calls), otherwise I will have to eat the $80. Not a good summer start.