1974 140 Merc with electronic ignition

[Dmark]

About a year ago I bought a 1974 Slickcraft SS 175 with a 140 hp Merc I/O ( model #21405). It looks like somewhere along the way it was upgraded to electronic ignition. So the question I have is will the electronic ignition upgrade affect how my tach works. Also, the electronic ignition should control timing advance...correct?

I am also trying to access my wot performance. According to the tach at wot I am running 2650 rpm and GPS speed is 33 mph. According to my calculations that comes out to about 11% slip with a 15p prop. But it just seems that my wot rpm is pretty low.

Tune up parts and carburetor are in fair condition. Accelerator pump seems to be working ok and it looks like the carb is all the way open at wot. Fuel pump/filters are new.

So I am looking for more rpm somewhere or a tach problem?

 

[bonzoscott]

Re: 1974 140 Merc with electronic ignition

Welcome to iboats! First make sure your throttle plates are fully opening at full throttle, looking down throat of carb. Second, you could pick up an inexpensive tach / dwell meter and check RPM on the lake to verify WOT RPM. A little difficult, have someone else drive while you check. Don't try WOT on muffs.