Re: 1974 Evinrude 9.9 won’t idle at low RPMs, need help

[Don]

Well, borrowing your brother’s carburetor would answer a lot of questions quickly! Changing the carb is kind of a pain, cuz you need to move the manual starter out of the way to get at one of the carb retaining nuts. Once the manual starter is loose, thread a 3/8 wingnut onto the thru bolt to hold everything together. Do not pull the thru bolt all the way out of that starter, there is a spacer/washer inside that you don’t want to dislocate. Be sure to get the starter cup locating tab back into its hole on the manifold during reinstallation as well.
And yes, there isn’t much movement in that mag plate when in neutral. But, there is an adjustment on the shift lever cam that will allow you to raise the neutral speed limit on this engine. Look on the right side of the engine where the shift lever connects to the shift detent cam, you will see the limit/stop that is retained with two screws. Simply loosen the two screws and move the stop forward to increase the neutral speed limit.
The throttle cam/carb sync isn’t too tough to do, I know it would help if I could provide some pictures. The thing to remember here is that the throttle plate on these engines is completely closed when idling. Look on the mag plate throttle cam, you will see a raised mark/arrow. Basically, the carb butterfly/throttle plate should be completely closed until the raised mark/arrow is in the middle of the carb throttle plate roller pick up. Unfortunately, the adjustment on this engine isn’t too easy because one of the cam retaining screws is sandwiched between the flywheel and mag plate! A quick test is to look at the throttle roller while the throttle is in its idle position, the mag plate throttle cam should not be touching the throttle roller. Slowly advance the throttle, the carb butterfly should just start to open when the raise cam mark is in the middle of the carb butterfly roller. Don’t get worried if the throttle plate starts to open only after the mark passed the middle of the roller, this will only cause a rough/rich off idle situation, which is not what you have going on. A carb butterfly that opens too early, or is still partially open at idle will spit/stall like your engine does. Keep in mind that just because the roller is not touching the cam does NOT guarantee the throttle plate is completely closed. A weak butterfly spring, or worn throttle plate could hold it open slightly. Your engine also has a recoil lock out that is connected the throttle plate roller linkage, this could cause the butterfly to be held open as well if things are stiff. Unfortunately, the only way to ensure the butterfly is closing completely at idle is to remove the carb and look at throttle plate movement from the back of the carb.
There is no way of telling whether the reed valves are broken/not seating properly unless you remove the intake manifold, let’s leave this for a later step if your brother’s carb doesn’t improve things and you don’t find sync/linkage problems.