New User - New Boat owner: engine dies as we push to accelerate

Peterko

Recruit
Joined
Jun 22, 2020
Messages
1
Evenrude 70hp 2 cycle motor model 70773s. Starts and idles fine. I can lift the idle arm (next to the speed lever) and idle it up to 30K rpms with no issue. At low RPMs (10K) forward and reverse work fine. When I go forward and try to go faster, the engine dies Here are the things I have tried:
1. New spark plugs (3)
2. New fuel supply line with new bulb
3. New/fresh fuel with SeaFoam added
4. New prop (thought the hub had failed in old prop)

The local repair shops are out five weeks before they can look at it. What else can I check, and in what order? Not sure what key terms to search on.

Thanks,

Peter
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
38,884
Well 30K rpm is pretty special.-----So start with a compression test and post your numbers.------Then a test for spark.----Good spark will jump a gap of 7/16" with ease.----They will rev up on a hose running on 2 of 3 cylinders !!
 

F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
28,226
Possible fuel starvation, but not necessarily. If it were me, the first thing I would look for is a sticky spark advance. Put shift in forward gear, then turn it off. Now disconnect the throttle cable from the motor and with your fingers on the lever where the cable was attached, push the lever toward the rear (aft). Watch the upper end of that long lever and the carburetors throttle shafts as you do it. As you push the lever rearward, the upper end should move forward. At the same time, the carburetor shafts should start to open, but just a little bit. As that upper end moves forward, it will bang up against the full advance stop, and can't move any further. NOW, and only now, the carburetors should open fully with further rearward movement of the bottom end of the lever.

Fault: If the carburetors open before the upper end reaches full advance, the timer base is sticky and lagging and the carbs are opening before full spark advance is reached. That will cause bogging or even stalling, which is what you are describing.

Hope this makes sense. I know what I'm saying, but it is difficult to put it in layman's language.
 

havoc_squad

Senior Chief Petty Officer
Joined
Mar 5, 2011
Messages
739
Well 30K rpm is pretty special.-----So start with a compression test and post your numbers.------Then a test for spark.----Good spark will jump a gap of 7/16" with ease.----They will rev up on a hose running on 2 of 3 cylinders !!

Even though I know the OP's RPM is a typo with an extra zero, I couldn't resist chuckling on reading this reply after seeing 10k and 30k RPM.

No ill will against the OP, glad they are asking here.

Any chance this is a jet turbine engine with the label "Evinrude" on it with that many RPMs stated?

Maybe BRP started making jet engines after they stopped making the E-Tec? No probably not, as most of the planes are parked due to lack of demand.
 
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