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70hp Mercury Mariner stalls going into gear

T

tooltym

New member
Hello everyone,
I have a 1977 Mercury Marine 700, 70hp two stroke that stalls as soon as it’s put into gear. Warm or cold it is the same. I have plenty of water at the tell tale. Carbs are clean. Fuel screen is clear. Plugs look fine and are Champion L76V. Compression is 140 psi on all three cylinders. It has about 4 psi of fuel pressure which holds after it stalls. I found one fuel hose dry rot cracked but not leaking and replaced it. I found the #2 cylinder plug wire high on resistance and replaced the set. I’ve replaced the primer bulb and hose. The tank vent seems fine and I’ve tried running it with the gas cap loose too. The fuel is fresh, without ethanol and mixed 50/1 with Pennzoil Marine Premium Plus. The bulb stays hard. It restarts easily, but as soon as you put it in gear it stalls. It idles smoothly in neutral around 1,000 RPM.

I’m at my wits end. It will idle all day in neutral. Throttle response with the warm up lever is good. It will run in gear on land with the ears attached, but as soon as it’s in the water it stalls. Any help I can get is greatly appreciated!
 
You have to set the low speed jets while the motor is warmed up and running in Forward gear in the water at about 1,100 rpm, turn them 1 1/4 turns out to start with - have someone drive while you turn them in or out until the motor accelerates smoothly.
 
I wasn't able to get that far because it would stall as soon as it's put into gear. I removed the fuel pump to inspect it and ended up replacing the diaphragm and gaskets. It will now run in gear and I have adjusted the carbs in forward gear. The issue it now has is when I roll into the throttle the motor bogs and stalls and then is difficult to restart. Could crank seals cause this? How can I test them?
 
racerone said:
Open carburetor slow speed mixture screws 1/8th turn at a time and test run.
Click to expand...
I never would have believed that the idle mixture would have so much effect on throttle response and upper end performance. It's amazing! Thank YOU @racerone and @Quicksilver ! I can't believe the difference this made. Going to put the airbox back on it now and do some fine tuning.
 
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