1986 Merc 850 stalls out of the hole.

[sweaver]

O.K. You Merc. guys, I need some real help! This motor is on a boat my son bought the first of the summer. I pulled the carbs. and installed kits after cleaning. I have checked sync,timing,compression, firing etc. Motor cranks and runs fine at idle. As the throttle is advanced the motor starts dying out like it is flooding and at full throttle it will shut off completely. You can back off the throttle and it will recover. Several times it did get up and run on plane only to eventually die out and cut off. Any suggestions??

 

[Vlad D Impeller]

Re: 1986 Merc 850 stalls out of the hole.

It could be a bad fuel pump

 

[dakk1]

Re: 1986 Merc 850 stalls out of the hole.

SF174<br /><br />Yes, check that fuel pump if you haven't already. If you believe you have eliminated fuel delivery as the problem, then I would look to the ignition system. Merc switchboxes and stators are common components that fail. You said you checked firing. So your getting good spark on all cylinders at idle? You might be losing spark under load due to a faulty stator or box. You really need a DVA (direct voltage adapter) to test. They cost about $40. Use with a multimeter. Also bad idle stabilizers and rectifiers have been known to cause those symptoms. You can eliminate those by disconnecting them and see if you still have the problem. If you have access to a inductive timing light you could hook it up and run the motor under load and see if your losing fire. Then there's the trigger, the coils, the flywheel etc. etc. Probably gonna need a manual.<br /><br />Dave..

 

[seascavanger]

Re: 1986 Merc 850 stalls out of the hole.

Sometimes a slow sqeeze on gasline bulb will help. Simple....but sweet

 

[sweaver]

Re: 1986 Merc 850 stalls out of the hole.

Thanks for all the advice. I forgot to say I rebuilt the fuel pump also. The kit included everything except the check valves. dakk1, where can I get a DVA and will it work on a Fluke digital? I did an Ohm test on the stator,trigger,coils and rectifier. They appeared to test good. I'm not familiar with the stabilizers. What and where might that be? I have hooked up the timing light but haven't used it while underway(load). Kind'a hard doing by yourself. Guess I'll need a driver to do that. I did set up the primary pickup and max timing. I haven't tested it since then.

 

[dakk1]

Re: 1986 Merc 850 stalls out of the hole.

SF174<br /><br />I bought my DVA from maxrules.com. I don't know that your motor has an idle stabilizer. Mine is behind the flywheel on my 1985 150hp. Yeah, kinda hard to test with the wind and the waves in your face. LOL. DVA will help a lot. Yes, it will work with a Fluke. Let us know what you find out and good luck.<br /><br />Dave..

 

[sweaver]

Re: 1986 Merc 850 stalls out of the hole.

Dave,<br />I also forgot to point out the motor runs great from idle to W.O.T. when you have it on the flush muffs. NO skips,loading up or stalling. I know this is a no load condition but I thought it might shed a little more light on the problem. Any furhter ideas?

 

[dakk1]

Re: 1986 Merc 850 stalls out of the hole.

SF174<br /><br />Unfortunately, the fact it runs great on the muffs means very little other than it will crank and run. When you get your DVA you will be able to do some meaningful tests that might solve your problem. Even then you may still have to test it under load. It's a pain in the rear unless you live on a lake. Nearest large lake to me is 35 miles. Not to be redundant, but are you sure you have eliminated fuel delivery? While running have you pumped the bulb, choked it, sprayed pre-mix in the carbs. Also, checked for ventilation, air leaks, restrictions, bad gas, run from a remote tank with known to be good gas? Just trying to touch all the bases. If you haven't already, take a good look at all your wiring. One guy wrote in with these symptoms and after much testing and pulling of hair, found that his mercury switch was grounding out! <br /><br />Dave..

 

[andy6374]

Re: 1986 Merc 850 stalls out of the hole.

SF174<br />Be careful with the muffs. You shouldn't rev the engine above 1000 RPM's with those.

 

[sweaver]

Re: 1986 Merc 850 stalls out of the hole.

Can I bypass the Mercury switch and run it? I tested everything but that. I figured either it works or doesn't. I will double check my fuel supply and lines. Thanks again for the help!

 

[dakk1]

Re: 1986 Merc 850 stalls out of the hole.

SF 174<br /><br />I doubt it's you mercury switch. You would be more likely to have no fire if it were that. Besides, your probably not that lucky. Too simple. LOL. Yes, you can disconnect it and/or Ohms test it. No continuity between black lead and terminal in down position. Continuity in up position.<br /><br />Dave..