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any idea's 40hp mariner 1984

J

joe bald

Member
OK, so here's the deal. My motor will run fine right out the get go for around 30minutes or so. Then I run into this struggling issue. I will try to go full throttle and this is what happens basically in full throttle it will slow way down and start missing and stutter , It idles a little rough at this point but it still runs at low speed and idle. Also, if i put it in neutral and back to full throttle again it will work for 10-15 seconds before the same issue occurs. Any ideas? :confused:

ps I recorded an audio of it running but it will not let me upload here
 
Definetly sounds like a fuel issue. How old are the fuel lines? Some of the old lines fail internally due to ethanol. Take the line off the connector to the motor and look for internal failure, usually looks like rusty coloured goo. Have you cleaned the fuel filter on the motor??
 
If its a fuel blockage, sits for a while the debris can loosen and when the fuel is being pulled thru it starts to block. This is just the basic start at trouble shooting it. Are your fuel lines old?? Grey lines??
 
They are not grey lines but appear older so I will try changing them and see what happens. Might be a few days though cuz work this week is a heavy schedule
 
I would take an end off and see what they look like inside first, just putting new lines on is just throwing money at it. Under the hood there should be a fuel filter, clean it out after looking at the fuel lines.
 
Try another fuel hose assembly as well. I had one where the check valve in the bulb would lock up now and then and kill the motor. Heard of others doing the same thing.

Jeff
 
so the fuel lines from the tank look clean. The gas coming out of it is clean. However, the gas in the fuel lines on the motor side is rust colored orange-brown. so probably an issue there? Checked the fuel filter. Clean fuel in there and the fuel pump, no build up. In fact, the only rust colored fuel I found was in the main fuel line connected to the fitting. Could it be a bad fitting? Any ideas appreciated
 
is it firing on all cylinders?
if not it could b a switch box. & u can find that out by putting in new plugs, run it for awhile& take out the plugs & c which one is clean. Also i recommend getting new coil packs W the switch box.
 
if it was a switchbox issue, I dont think it would run flawless for as long as it does, and from what i understand it wouldnt stay running
 
I'm still having issues.. Long story short changed out the fuel hoses on the motor tried runnin it with different take and no change.. Compression still good I even tried a friends switch box and same thing.. Could it be bad spark plugs? Fuel pump? I'm out of ideas
 
Did you ever clean/rebuild the carbs? The rust colored fuel would be in the carbs...perhaps a slug is floating around in the bowls causing intermittent blockage.
 
He may be onto the problem.

On two separate OBs of mine, a slug of brownish crud someone got into a carb and messed up the motor just like you describe. What it was--and how it got there--remains a mystery (and a frustration since it could happen again). I have all new lines and a nice filter after the fuel pump (where it belongs), but...

The carbs have to come apart to see if that's it.

Jeff
 
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