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2000 50HP Bigfoot has me stumped

M

Mcadieux

New member
Having an issue with a 2000 Mercury 50hp bigfoot. The summer before last it started giving me issues where it had no top end and would run very rough anytime I tried to go over 2500rpm. Last summer it wasn't used. This summer, before putting it back in I cleaned the carbs. Put the boat in and it ran great for about an hour. No issues at low RPM or WOT. Suddenly, I lost the top end again with it refusing to run above the 2000s and running very rough even just above idle. I pulled the carbs and again cleaned them, using an ultrasonic cleaner, carb cleaner, torch cleaning tools, and an air compressor. They were absolutely spotless. Put the carbs back on and the motor sounded and ran to perfection for about 15minutes before again running rough and not throttling above 2500 or so. No change in running condition if I pump the bulb and the bulb stays hard.

So Far:
New fuel tank
New Fuel Filter
New Fuel Pump
Cleaned carbs with new orings
checked Stator, Coils, all switches and sensors
Spark plugs replaced and spark plug wires inspected
Tried running with fuel cap loose to rule out venting issue – no change
Fuel is fresh
New Thermostat

It appears to be a fuel flow issue, I'm not sure how the carbs could have clogged again within 15min. I ran the fuel system dry and put in a new fuel filter before reinstalling carbs.

Anyone have ideas on what to try next? I feel like nothing fits as a possible problem
 
racerone said:
Water pump impeller changed ?
Click to expand...
I have not changed the waterpump and its been a couple of years. Could that really cause what I am seeing? I feel like the fact it ran well again after removing and reattaching the carbs means it has to be carb / fuel related/


fitz73222 said:
Re-check stator, how did you check it? Did you measure peak voltage? Is this engine 2 stroke or 4 stroke?
Click to expand...
Stator I checked the resistance according to the repair manual. Whats confusing me is the fact it started running well again and only thing I changed was the thermostat and cleaned the carbs. But I can't understand how the can clog again in minutes. It's a 4 Stroke
 
Un problème de pompe à carburant est souvent le cas il se limite en puissance changer la pompe à carburant problème au niveau de la membrane à dépression
 
Vidanger le tuyau d'essence pour retirer les éventuelles résidus avant de recommencer en appuyant sur la perle et en appuyant sur la pompe.
C’ est souvent un détail négligé et on rebouche tout d’ un coup il faut être sûr de partir sur une base propre
 
Mcadieux said:
Having an issue with a 2000 Mercury 50hp bigfoot. The summer before last it started giving me issues where it had no top end and would run very rough anytime I tried to go over 2500rpm. Last summer it wasn't used. This summer, before putting it back in I cleaned the carbs. Put the boat in and it ran great for about an hour. No issues at low RPM or WOT. Suddenly, I lost the top end again with it refusing to run above the 2000s and running very rough even just above idle. I pulled the carbs and again cleaned them, using an ultrasonic cleaner, carb cleaner, torch cleaning tools, and an air compressor. They were absolutely spotless. Put the carbs back on and the motor sounded and ran to perfection for about 15minutes before again running rough and not throttling above 2500 or so. No change in running condition if I pump the bulb and the bulb stays hard.

So Far:
New fuel tank
New Fuel Filter
New Fuel Pump
Cleaned carbs with new orings
checked Stator, Coils, all switches and sensors
Spark plugs replaced and spark plug wires inspected
Tried running with fuel cap loose to rule out venting issue – no change
Fuel is fresh
New Thermostat

It appears to be a fuel flow issue, I'm not sure how the carbs could have clogged again within 15min. I ran the fuel system dry and put in a new fuel filter before reinstalling carbs.

Anyone have ideas on what to try next? I feel like nothing fits as a possible problem
Click to expand...
Does this have CDI system? (little box that tells the coils when to fire)? I have a 1986 50 hp Mariner that was giving me intermittent problems similar to what you are describing and sometimes it would run OK for a while even. Through diagnosis, I concluded that I didn't have spark to one of my plugs....I tested the coil to be good. Then I tested all the DVA readings and resistances from the stator and triggers and they were pretty much at spec. The CDI box is the only thing that really can't be diagnosed by itself....if all the signals to the CDI are good and the wires and coils from the CDI to the spark plugs are good then by elimination, the CDI box must be bad. I bought a used CDI off ebay for $40 and it has run as good as new for 2 years now.
 
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