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Mariner 40 ?

ILMORdude

ILMORdude

Sponsor / Charter Member
Im not real familiar with OB's. My Unc has 1 of these and it keeps cutting out when at WOT and dies. But it fires right back up. It has spark and compression but the bottom cyl is a bit weaker. I jerked the automix out and mixed the fuel, new plugs, and cleaned the carbs a bit. Seems to run smoother. Im looking for any tips!! Thx
 
90% of the problems I have seen/had with smaller outboards is in the fuel system. Is the fuel line good including the o-rings in the quick releases? What about the fuel filter and the fuel lines on the motor itself? I am assuming the vent is open on the tank. I had a 25 merc that would do the same thing, it finally ended up being a mud dobber nest in the exhaust that was choking it out at higher rpms. :rolleyes:
 
Do you have to pump the primer bulb to get it to restart? Does the bulb collapse? Will it keep running if you pump the bulb? When motors die at WOT sometimes it is a precursor to big problems. The only thing worse is surging at WOT.
 
MOBILEMERCMAN said:
Do you have to pump the primer bulb to get it to restart? Does the bulb collapse? Will it keep running if you pump the bulb? When motors die at WOT sometimes it is a precursor to big problems. The only thing worse is surging at WOT.
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Bulb was soft with autoblend hooked up. After removing that system and pre-mixing the fuel, bulb seems to hold prime very well. Running on the hose after these mods, engine seemed to run better. If you pump while running it does respond and stumbles. Water testing asap to see if WOT run will result in the stall. I know the bottom cyl is not great but im hoping its ok "for now"
 
You said cleaned the carbs a bit? Did those needles and seats have springs? When you pump the bulb it should get hard when the bowls fill. If it stumbles when you pump it the floats are not controlling the level. If it has springs you can force fuel by so only pump until firm. It should not stumble by pumping it. If a carb is dumping it wont idle well. The idle circuit on outboard carbs is part of the whole flow needed at speed.

So when you test it see if the bulb stays full at speed. It may not get firm but you should feel fuel in it. If it is running out of fuel completely and dies the bulb will tell you. If it is leaning and sticking the piston as it expands it will also cut off and die. That may be why the lower cylinder is low already. So be careful not to kill it.

Does that motor have shutters for choke or an enrichment valve. If it doesn't have shutters and you push the key in as it is dying. If it runs better that is telling you you need to clean the carbs. The choke in that case dumps fuel from the top bowl directly behind the shutters on the lower cylinders.

If you get the serial number of the motor I may be able to help you with more specific info.
 
It does have shutters. Can't tell if the needle has a spring by the break down.

So to keep it simple. Test and see if its running out of fuel to carbs or leaning out. You can also use a timing light to see if it is losing spark at speed. Percentage wise I would guess it is in the carbs. The passages are small in the little motors and it doesn't take much to mess them up. On the compression. How low is a little?
 
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