Home › Forum › Ask A Member › 1974 Evinrude 9.9 won’t idle at low RPMs, need help › Re: 1974 Evinrude 9.9 won’t idle at low RPMs, need help
This could be a carb synchronization problem, a throttle plate that is not closing properly/improperly adjusted/partially stuck open would cause the exact running symptom you are experiencing. These early engines had some funky lockout linkages that were connected to the throttle butterfly, I have seen many that were stiff causing the throttle plate not to close fully. Someone may have messed with the synchronization and messed it up as well, causing the throttle plate to be held partially open at idle.
You have had this carb apart, and it looked clean inside. Generally speaking, these are pretty rugged/simple carbs, but it surely is possible to have a plugged idle passage that can only be investigated by removing the welch plug. This is not a difficult operation, but the mixing pocket is very shallow, so extreme care must be used when drilling through the plug. The simplest way to rule out carb problems is by just trying out a different carb on the engine, but I am assuming you don’t have access to another carburetor.
You may have an intake manifold problem, bad gaskets, or broken/bent reed valves. Does it look like the intake manifold has been off before, do the bolts look tampered with? I don’t recall upper/lower seals being a big issue with these engines, but anything is possible. But, like Casey says, you would probably see evidence of oil drooling down under the mag plate if there was a problem.
You mention that you just bought this engine, so I am assuming it has never run properly for you, is that correct? Did you get any service history when you bought it?
Remember, stick to the simple stuff, most problems are simple until we confuse things by digging into bigger issues and creating more confusion. You have picked a real challenge for your first project!
No it has never ran properly for me. It’s just been a series of trial and error (lots of error). I was not given a service history, the guy just said he doesn’t want to tinker.
The bro in law showed me the fuel pump trick (he has been a huge help with everything so far as well). It didn’t change the condition. He actually has a ’75, I might be able to try out a different carb actually.
There are no signs of tampering, structural damage, or bent reed valves. When you talk about the carb synch, when you refer to the throttle plate, is that the reed valve that is at the back? Not the one that is the choke. If so, that was flush. Is that controlled by the cam follower? As for the carb synch, do you have any links where I can read more about that? I actually thought about that when I was working on it, but I didn’t take good enough pictures. I guess the best way I could describe it, is that it seemed like the throttle was restricted. The cam follower barely moves.