Re: How to get a few more rpm from my engine?? Please Help...
Sorry, I was starting to feel like a certain former FEMA director. (Perhaps you've heard the latest scandal in the States?)
<br /><br />Regarding the jets. You need to answer that question yourself. The single best way to do that is to have a look how your sparkplugs are burning. Different jets perform differently in different locations and different applications. In a nutshell, they shouldn't look wet or dry. There should be a slight sheen as if damp. The closer to tan deposits, the leaner the mixture. The closer to black, the richer. You want something inbetween. Closer to tan gives you the most power but you flirt with detonating a piston or two. Too black and you carbon-up and break rings. You probably want to be on the light side of brown to get the most out of your package, but not tan. The unfortunate part is that you probably have surface gap plugs. Same rules apply, but conventional plugs are much easier to read.<br /><br />Regarding the prop. You want maximum rated RPMs to get the full horsepower from your motor. More horsepower generally translates to more speed. So for the most speed from that prop, you probably want to have it repitched an inch lower, maybe two. That's your only option other than grinding away at the thickness of the blades or playing with the cup.<br /><br />Addendum: That's an even pitch. 4-blade props usually come in even pitches. I don't know why, but it seems like the inlines don't push a 4-blade too well. I would think 18 would be a fairly low pitch otherwise. You usually see those with 3-blade 19s or 21s and they turn them fine (depending on the boat, of course). Performance props of the era had two blades. Also, Merc Towers Love RPMs. 6,000 wouldn't scare me.
