BF50a max RPM seem low. What should I look at first?

[Slartibartfast]

So I finally got the boat launched for the season, and everything seems peachy except for one thing: my BF50a only gets to 4000RPM at wide open throttle. I am brand spanking new to this motor and outboards of this size in general, so am wondering where to start looking. I'm running a 3 blade 11 3/4x10 propeller, and from my research I should be able to hit 5500-6000 with that, correct?

Is there something I should look at tuning on the engine? I just spent a fair bit having it professionally set up for the season, so would be a bit disappointed if things aren't tuned correctly.

As for details that I don't think are relevant, but am too stupid to be certain, at 4k I was hitting 9.6 knots per GPS with the mast up, ballast empty, just me, minimal gear, and 6 gallons of fuel.

[Starscream]

My original BF50A needed an 11.8" X 9" 4-blade prop to hit 6k rpm, and could do 8mph ballast in and 16mph ballast out. The prop was Honda branded but I believe it was manufactured by Solas.

That's pretty close to what you have, and it seems to me that your motor/prop combo should be doing much better than it is.

Is the prop a composite-blade one? I ask because some of those have strakes on the blades that drop the rpm a lot.

How about the boat's hull condition? I presume from your post that it's cleean, not dragging a "garden" of growth? Have to ask though.

How old are the fuel lines and fittings? I once had an Amazon fuel line that had an inner plastic liner that started to come loose and clog the flow. Never again, Amazon, never again. Just brand named stuff from then on.

How about the fuel filter inside the motor? It's easy to check. Change the plugs?

Verify that the throttle handle actually moves the throttle linkage to full open? From memory you can see that happening with the motor cover off.

Not much help, sorry. Fuel, spark, air, prop... that's about all I know to check. Well, and gauges, I learned from a previous post, but your 4krpm matches your speed so the gauges aren't likely to be your problem.

Good luck

[Slartibartfast]

Is the prop a composite-blade one? I ask because some of those have strakes on the blades that drop the rpm a lot.

How about the boat's hull condition? I presume from your post that it's cleean, not dragging a "garden" of growth? Have to ask though.

How old are the fuel lines and fittings? I once had an Amazon fuel line that had an inner plastic liner that started to come loose and clog the flow. Never again, Amazon, never again. Just brand named stuff from then on.

How about the fuel filter inside the motor? It's easy to check. Change the plugs?

Verify that the throttle handle actually moves the throttle linkage to full open? From memory you can see that happening with the motor cover off.

Good luck

Basic aluminum prop. This one, specifically: https://www.amazon.com/dp/B085632TX2?re ... h=1&psc=1

Hull is clean, though without any fancy bottom paint.

Fuel tank and lines are brand new, but they did come from Amazon, so you might be onto something there. I'm not certain that they are the cause of this specific problem, but they don't have a great, confidence inspiring feel to them.

Fuel filter and plugs SHOULD be golden, since I just got it serviced at a dealer, and spent a couple of boat bucks on that . But maybe they're not great at their job.

Based on how things feel, you might be right about the throttle linkage. Once I started up, everything ran without a hiccup other than topping out at 4k with the control pushed all the way forward. I bet even I can figure out how to adjust that. Will take a look in the morning.

[Be Free]

Throttle linkage is a possibility. It is easy to see if the throttle cable is working correctly if you remove the engine cover. It is also easy to adjust if you find a problem. Move the throttle to full and see if the carb linkage moves to its wide-open stop.

Did your engine work include a carburetor rebuild and resynchronization? If the three carbs are not properly synched you will have problems and not hitting full RPM is a common one.

Another easy place to check is the spark plugs and wires. 4000 rpm is about 2/3 of max so you might have one plug, coil, or wire that is not working correctly.

I don't think your prop is the problem. If anything it may be a little small and that would make your RPM too high. I can hit 5000 with a 12x10 on my BF40.

[Slartibartfast]

So I haven't had a chance to adjust anything yet, but was motoring along last evening at 4k when, pretty suddenly, it jumped to 4800 and stayed there without issue. Any thoughts?

Not long after, I seem to have snagged a floating clod of mud and junk that chewed my prop just a little bit, but that's not really related.

[Be Free]

Things that happen suddenly are often electrical. Plugs, plug wires, and coil (each cylinder has it's own coil) would be top of my list.