Crusader won't break 2100 RPM's

[Jab]

The Crusader engine in my '78 Santa Cruz 2866 won't break 2100 RPM.

The good news- I don't need it to. We use the boat mostly as a floating lake camp. In the summer I work from it. At 1800 RPM's it runs 7.5 kts, which is fine for our cruising needs. When we want to go fast, we use a different boat.

The engine starts easily and runs fine. No stalling or misfires. No steam or smoke. No overheating. No 'milky' oil. We use 91 octane ethanol-free fuel.

I will have our marina mechanic check her out. I'd like to be able to ask some intelligent questions (or at least understand half of what he tells me).

My reading makes me guess a fuel restriction problem? Planning to check fuel lines, anti-siphon valves, and mechanical fuel pump, water separator and fuel filters, and clean carb.

What other questions should I be asking?

Thanks... JB

[waybomb]

First would be to check the throttle cable. When full open, is the carburetor butterfly fully open? You may be able to adjust the cable.

If the fuel filters (in carb and external) are fine, my next two guesses would be a partially blocked/stuck anti-siphon valve or bugs have built nests in your fuel tank vent fittings and are partially blocking the screen.

Let us know what you find.

[Lyndon670]

"The Crusader engine in my '78 Santa Cruz 2866 won't break 2100 RPM."

Is that in gear, or in neutral?

[Jab]

Actually, haven't pushed it to WOT in neutral.
If I get 3600 RPM in neutral, and only 2100 in gear, what else does that add to the list?

[Lyndon670]

Drivetrain up to/including props. I'd start with a visual on the props. If no damage and boat new to you, probably under propped.

[Jab]

Actually, the prop is about the only thing I know is good! It was pretty badly "dinged" when I got it. Prior to launch I had the marina check the size, and had it restored.

Just curious- would under-propped affect RPMs, or speed at any given RPMs, or both?

[Lyndon670]

It absolutely would. Simplistic comparison but paints the picture. Imagine you are riding a bicycle that has 24" wheels and you can go 30mph when you pedal as hard as you can. Now, take the same bicycle and put 20" wheels on it - do you think you could pedal 30mph if you pedal as fast as you can? Same physics applies to props, only it is compounded by not only the diameter of the prop, but also the pitch of the blade.

You can destroy a motor very quickly if you have a prop under/over what is recommended.

[Jab]

So... Turns out I can get about 3500 RPM in neutral at the dock.
Under way I get to 2000 RPM with about 1/3 throttle (meaning 1/3 travel on the throttle lever)), and only about 2200 with WOT.

[waybomb]

Have you checked timing?

[Lyndon670]

That's way low WOT in neutral. As waybomb says, check timing, check fuel. Make sure your secondary's in the carb are opening FULL.