Hi everyone,
We have a 1976 70 hp Evinrude that is experiencing an intermittent hesitation when going to full throttle.
The engine starts and idles beautifully, usually on the first turn of the key hot or cold. It will troll all day long and runs beautiful wide open. The problem only manifests itself after the engine has been idling or running at low speed for a while. I haven't nailed it down, but if wide open throttle isnt achieved withing roughly half a minute of startup, the engine will hesitate and bog. It'll eventually reach plane and smarten up and then run beautifully.
If I raise the idle with the warm up lever and "clear it out" just before going to full throttle, it seems to behave relatively normally.
If it idles or trolls for an extended period, beyond say half a minute, jumping to full throttle usually stalls the engine. A quick restart and a bit of warm up lever clears it out and away it goes.
If I'm cruising at full throttle, I can back out of it and bring the boat to a stand still and it'll accelerate normally again if it doesn't sit too long.
The carbs were cleaned and rebuilt last summer with Sierra kits. I used a piece of mechanics wire on each jet to make sure they were clean and blew each one out with compressed air. They are very clean.
Spark jumps a 7/16" gap easily and is nice and blue and plugs are new champions at .030"
Compression is around 100-105 for each cylinder cold.
All fuel lines are new urethane 3/8" line and the fuel pump and filter are new. The tank vent is open and the primer bulb never goes soft.
I have previously checked the timing using Joe Reeves method and found it to be slightly over advanced (we did replace a timer base last year due to a broken part which could explain that). Since backing it off a few degrees the motor generally seems happier in all RPM ranges but still has this hesitation. Spec is 17 degrees, so using Joes method I set it as close to 13 as I could get it.
I checked the link/sync of the carbs and everything looks dead on.
I'm otherwise happy with the performance of this little motor, except this hesitation is a pain when trying to pull a skier out of the water.
Any thoughts would be appreciated.
Thanks
-Aaron
We have a 1976 70 hp Evinrude that is experiencing an intermittent hesitation when going to full throttle.
The engine starts and idles beautifully, usually on the first turn of the key hot or cold. It will troll all day long and runs beautiful wide open. The problem only manifests itself after the engine has been idling or running at low speed for a while. I haven't nailed it down, but if wide open throttle isnt achieved withing roughly half a minute of startup, the engine will hesitate and bog. It'll eventually reach plane and smarten up and then run beautifully.
If I raise the idle with the warm up lever and "clear it out" just before going to full throttle, it seems to behave relatively normally.
If it idles or trolls for an extended period, beyond say half a minute, jumping to full throttle usually stalls the engine. A quick restart and a bit of warm up lever clears it out and away it goes.
If I'm cruising at full throttle, I can back out of it and bring the boat to a stand still and it'll accelerate normally again if it doesn't sit too long.
The carbs were cleaned and rebuilt last summer with Sierra kits. I used a piece of mechanics wire on each jet to make sure they were clean and blew each one out with compressed air. They are very clean.
Spark jumps a 7/16" gap easily and is nice and blue and plugs are new champions at .030"
Compression is around 100-105 for each cylinder cold.
All fuel lines are new urethane 3/8" line and the fuel pump and filter are new. The tank vent is open and the primer bulb never goes soft.
I have previously checked the timing using Joe Reeves method and found it to be slightly over advanced (we did replace a timer base last year due to a broken part which could explain that). Since backing it off a few degrees the motor generally seems happier in all RPM ranges but still has this hesitation. Spec is 17 degrees, so using Joes method I set it as close to 13 as I could get it.
I checked the link/sync of the carbs and everything looks dead on.
I'm otherwise happy with the performance of this little motor, except this hesitation is a pain when trying to pull a skier out of the water.
Any thoughts would be appreciated.
Thanks
-Aaron