888 Mercruiser RPM's fluxuate at low speeds

[searaychad]

At idle to about 1200 RPM's I cannot keep the engine at a specific RPM.It's an older boat,1973 srv 180 with the 302 ford 188hp.Any suggestions?Also I have a 19 pitch stainless prop and it seems to rev up too high.Would a 23 pitch be too much?

 

[aqua*holic]

The idle problem could be quite a few things. When you say you can't keep a specific RPM does that mean the engine is surging up and down? Does it jump around and hold for a little bit? What is your vacuum reading at idle? Have you done any maintenance to it recently?

Interesting on the prop. Mine has a 17 pitch and hits about 4,600 rpm. They say for every inch change in pitch will produce about 200 rpm change in the engine. Just a rule of thumb for I/O's.