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Mercury 70HP Blueband stalls only on quick acceleration but not gradual

A

Axworthy

New member
Hi Everyone, I have been reading these forums for sometime and they have been a great help but can't find anyone with this problem.

The serial for my engine is: 9365833

When I first got the engine I knew it had a problem accelerating under load so I have done the following:

Fuel tank and line going to engine changed
Fuel connector from tank to engine changed
New spark plugs
New HT leads
Cleaned the fuel filter on engine
Checked compression
Checked fuel diaphragm
General clean up and carb cleaner sprayed through carb

After completing the above I took the boat out and had 2 problems

1. The boat seems to only start even when hot using the throttle
2. If extremely slowly accelerating or decelerating the engine is fine but any quick speeding up or slowing down the engine stalls

Thinking this might be carb relating they are now off and sitting in cleaner and I have rebuild kits for them. They were not too dirty but some debris in there. Anyone got any other suggestions?

Thanks Pete
 
Thanks for your replies.

Are the soft plugs the 3 round silver caps? I can't figure out how yo remove these, I do have new ones.

thanks
 
When its all back together, find your best idle mixture adjustment (boat on trailer or tied to a dock), then ad 1/4 to 1/2 turn OUT (CCW). That helps a lot.

Jeff
 
Hi everyone, carbs are now ready to go back on engine. Check valve and fuel pump kit on order. I just want to check is engine timing essential as other than an acceleration issue it was very smooth running. The timing maintenance looks fairly complicated compared to just adjusting idle mixture screw.
 
Timing is fixed at the factory and generally needs no adjustment for the life of the motor.--But if somebody messed with it ??
 
Ok I should be fine then. I also noticed where the carbs mount on the engine the surface is quite scratched. Would this cause a problem or will the gasket still seal ok? No idea how it's been scratched.
 
Hi Everyone, quick update. Carbs all rebuilt and back on. First 5 mins it kept stalling but after a bit of adjustment I've had 2 great trips out. Thank you for your help.

i have a couple more questions:

1. I changed the impeller and water pump gaskets but after putting back together I've noticed when on land water is escaping between shaft and lower gear box unit but when I took it apart there was no gasket for that. There is plenty of water coming out the nozzle on engine and a bit from the exhaust holes.

2. When at almost full speed, when I push the throttle to max I hear the engine increase and speed but it only lasts about 3 seconds before slowing slightly. Any ideas what this could be?

Thanks. Peter
 
1. I changed the impeller and water pump gaskets but after putting back together I've noticed when on land water is escaping between shaft and lower gear box unit but when I took it apart there was no gasket for that. There is plenty of water coming out the nozzle on engine and a bit from the exhaust holes.

Normal.


2. When at almost full speed, when I push the throttle to max I hear the engine increase and speed but it only lasts about 3 seconds before slowing slightly. Any ideas what this could be?

Yes: TOO MUCH Timing! Time it with a timing light IMMEDIATELY or you'll fry pistons. You want about 21 degrees advancer (less than specified thanks to today's crappy gas).

Trust me on this!

Jeff
 
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