Re: WOT Engine RPMs and Prop Pitch for Rebuilt 25 hp Evinrude
Yes, this is an old thread that thill has resurrected and "Salt" has gone dark after 34 posts...
That said. For others contemplating porting and new carbs, nearly always carb jetting has to be dialed in and also where the peak power band will occur.
Carb jetting can be a PIA, and bigger jets can often be the wrong direction.
If the shop has already built these before and dialed everything in, great. You've just scored a lot of free R&D.
In this case, it does not seem so. It's not producing any where near 40hp as it sits and based on those plugs, it's too rich.
I don't know the water temps and head temps at full throttle. It may be OK. But he may be wise to put the thermostat back in, especially for low speed.
It's helpful to have a good tack. The Tiny tach is a bit slow updating, which is important for WOT runs, since a slightly too lean setting will run quickly up to a high rpm, then start to drop as the piston overheats and swells in the bore.
Sticking a piston can happen quickly, so you need a fast tach response time, but you're not even close to that, at this point.
A PET Tach is a better option. You can probably find used ones for less than $100. You are tuning for max rpm.
The SST prop you have should work great. Just get your jetting set correctly and it will rev plenty if the porting was done correctly.
Be careful raising that motor too high as that has a very high water pickup, just below the A/V plate.
Regardless what the spark plug crossover book says, the B7HS is a slightly hotter plug than the L77jc4.
Just thought I'd try to give future "Searchers" a bone, rather than a dead end after reading through 35 Posts.
Maybe Salt with be back with his final results.
