Mercury 900 90HP Stall

[svtcbra302]

I have a 1964 Mercury 900 Series 90 Horsepower. I just bought the boat and motor. The weird thing is, out of the water, with the garden hose hooked up to the motor, the motor revs fine and runs absolutely great. However, when I go to the river and have the whole motor in the water, I put the motor in gear, it idles down to a chug and then shuts off. I am thinking this could be a spark plug problem. When there is no strain on the prop when it is out of water the motor runs great, it only stalls whenever it is in the water and is being put in gear. Someone help me!!! Thanks

 

[RICKRICK1]

Re: Mercury 900 90HP Stall

Swiss6 first thing do a compression check on all cylinders they schould read over100 and be within 10% of each other. Then you need to adjust your idle in the water and not on the hose. Idle needs to be adjusted in gear. Adjusting idle and carbs on the hose give false numbers as there is no back pressure. If you are still having problems you might try and enrich the carbs 1/4 turn out.<br /><br />Lastly you maybe having carb problems due to junk in carbs or blocked orfices in the carb and need to overhaul them. I would try the first two things then do a carb overhaul. If you do the carb overhaul make sure you have a manual which descrbes how to and also do a link and sync after wards.