1977 70 hp Evinrude Bogging at Mid throttle

Weirdboymike

Seaman
Joined
Apr 9, 2015
Messages
59
Hey guys/gals,

I have what appears to be a very common issue with these motors. I have a 1977 70 hp evinrude O/B model 70773s and it runs like a champ... as long as you know how to run it. It idles great, runs great at low speeds and high speeds, but in order to get to the high speed I need to get through the Bog Spot at mid range. I accomplish this by popping the choke real quick. Once I am up past this spot I'm golden. I see everything for theories on this from too much air, not enough gas, safety kill kicking in, thermostat, etc. There are many people posting this topic but they never come back to say what fixed it (if they were fixed). It's not a big enough problem to where I don't trust my motor, it's just a little annoying. I'd say it happens at least 2 out of 3 times. I've hear that bumping up the jets one size could work but I have also heard it didn't do diddly. I have also heard the posts running through the carbs that hold the valves can wear the carb bodies allowing too much air in and that it can be fixed by applying a heavy grease around them. I tried that and no luck. Fuel pump was changed last year. I am in the middle of restoring the boat and have the tank out so I will be checking the screen for build up since I have to change the sender anyway. I have also replaced the fuel line and primer last year. I changed out one of the coils as well a few seasons ago and I am thinking of changing the other 2 or all three again just to do it. This issue has plagued this motor ever since I can remember using it (back in high school about 10 years ago). Could it be carbon build up or something? I had the carbs professionally done about 2 seasons ago and I realize its probably about time to do them again but that didn't solve the issue back then either. Anyone have this problem and fix it? Please advise! I am pretty familiar with this outboard and can do most of the work myself but do occasionally need guidance.
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,041
Most carburetor problems turn out to be something else.------If fuel is run out of the carburetors when boat comes out of the water they will stay clean.--Should not need to be done every 2 years.----Certainly an easy job to do yourself if you insist they are part of the problem.---Report the results of a compression test.----Try running the motor on a known good portable tank and hose.
 
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