idle rpms suddenly increase

[dave37]

Was winterizing my 73 50 hp 4cyl Merc this week, had it on muffs and after a couple of minutes running the rpms increased noticeably, not a huge amount, but a noticeable increase, probably a couple of hundred rpm. Wondering if this is a sign of anything ominous or just happening because it's warming up, never noticed it doing this before.

 

[j_martin]

Re: idle rpms suddenly increase

Suckin' air, fuel leaning out, timing change. Worth investigating a little. Some of these things could hurt.

Question comes to mind. Did you add something like sea-foam to the fuel and maybe it sped up when the new mix hit the engine? Might be normal.

hope it helps
John

 

[dave37]

Re: idle rpms suddenly increase

I had added fuel stabilizer (not sea foam) to the tanks, and the distributor drive belt is rather loose and in need of replacement but has been for some time. Also, as I noted on a previous post I ran the motor for a few minutes without the water pump working (discovered the shop that repaired my propshaft had mangled the water pump impeller and it took a few minutes-and only a few minutes--to figure out what was going on before shutting it down). I'm hoping that isn't the cause of the rpm increase.

It does it every time though, runs for a couple of minutes (with water pump corrected) and then speeds up a bit like clockwork.