79’ Evinrude 70 Bogging

I have a 1979 Evinrude 70 (70973R) when I put it in gear and give it throttle, it’s tends to bog down and die, after some finesse with the throttle I can get past it and it runs amazing at WOT. The other thing I noticed is it doesn’t like to idle at low RPM, it takes about 1200-1300 RPM in neutral in the water to keep It running while in gear in the water, if I put it in gear with the idle adjusted any lower, it dies. I’d like to try and get a lower neutral ideally because it shifts really hard at that RPM. It runs great on muffs. I’ve tried choking it and pumping the primer bulb when it stumbles and it makes no difference. It has a 13.75/15 prop on it that’s had the vents added per the OMC SB. It has new ignition coils, a new power pack, new spark plugs, new fuel lines, a good primer bulb. And the carbs have been cleaned recently.

You start with a compression test.----Post the actual values you get on this 45 year old fine ( when new ) motor.

racerone said:

You start with a compression test.----Post the actual values you get on this 45 year old fine ( when new ) motor.

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I did compression test about 3 weeks ago. All three cylinders were a little over 130.

Fuel pump diaphragm checked?----Reed valves checked ?-----Flywheel key checked ?----Perhaps throttle plates are opening too early.

racerone said:

Fuel pump diaphragm checked?----Reed valves checked ?-----Flywheel key checked ?----Perhaps throttle plates are opening too early.

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Reed valves are good, I haven’t checked the fuel pump or the flywheel key.

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racerone said:

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Fuel pump seems okay, the diaphragm isn’t stiff or broken.
How do I check the flywheel key, and if the throttle plates are opening and too soon?

carbs cleaned recently... do you mean removed, orifices cleaned out float checked out etc...

these are old style carbs easy to clean up incl.. side channel for LS upper drip chamber under the die size plug which feeds fuel for idling properly .

jpjourdonnais said:

Fuel pump seems okay, the diaphragm isn’t stiff or broken.
How do I check the flywheel key, and if the throttle plates are opening and too soon?

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It is easy to see if the Throttle Valves are fully open, by looking down the Carb Throat.
A check of the Link and Sync will verify proper Carb Opening, in relation to Spark Advance. That needs to be checked and if needed, adjusted any time a Carb is taken off.

The carbs were completely rebuilt by a local shop. In addition I cleaned them all myself, including running a single strand wire through all the jets. The carbs are spotless.

Throttle valves fully open in sync. And are synced when at idle as well. I’ll run through the procedure again.

A took it out a ran it to get a gauge of where it’s at now, and the bogging during acceleration only comes after long periods of idling. At idle in gear, it starts out around 1000rpm and slowly loses RPM over the course of a minute or two until it gets to about the mid 700s. Then it starts to stall out and die. But what i found is if I do a quick bump of the choke during that period after it hits the mid 700s to when it fully stalls, it recovers itself back to the 1000rpm and the process repeats. If I bump the choke too early, it causes it to die. (This is a new symptom)
Mind you when I say bump the choke, it’s quite literally just a quick tap of the key button.

If I bring it out of the idle detent and throttle it up to about 1200-1500 rpm, it’ll go all day long. Same with at any RPM above that.