First boat, rpms too high?

[Part-time]

Re: First boat, rpms too high?

The RPM or pulse switch on the tach is not always obvious but sould still be there.
Here are a few examples.

 

[QC]

Re: First boat, rpms too high?

Thank you ^^^^

Important to note that the numbers don't always correspond to cylinders. Very few 5 Cyl Volvo engines in boats Like none. So the point is that you still may need info to get this right.

 

[ba1335]

Re: First boat, rpms too high?

Good call. Took a picture of the tach Prop and out drive sn. Any insight? .........I guess I can't load them from the iPad. The tach does have the selector switch and it is set at 2p/4c (other options, 4p/8c, 3p/6c). The prop serial number is 48-78120-19. Mercruiser sn is OF846613.

 

[QC]

Re: First boat, rpms too high?

The prop is right for an Alpha, and it is a 14 inch diameter. So that should be out of the way.

 

[ba1335]

Re: First boat, rpms too high?



Pictures if they're still needed. What should I do next? Also, is it 'appropriate' to look into buying a new boat so I can test drive it to hear what the engine should sound like?

 

[fishrdan]

Re: First boat, rpms too high?

The tach does have the selector switch and it is set at 2p/4c (other options, 4p/8c, 3p/6c).

2 pole / 4 cylinder, your tach has the selector switch set properly. You could rotate the switch a couple times to clean the contacts, to see if that makes a difference, just set it back to 2P/4C. If you have a shop tach, you can compare it against your dash tach, to see if the dash tach is off. Or if you have an automotive tach, you could swap it in for testing, then replace the dash tach if it's found to be defective. Who is the manufacturer of the tach? I had a dead Faria and they swapped it out for $25 or so.

(BTW, those wire nuts under the dash are a no-no and will eventually cause problems, change them over to crimp connectors.)

 

[sasada]

Re: First boat, rpms too high?

Hey there ba1335...Sorry to sound to abrupt but what you NEED to do next is have your tach checked...That is the bottom line. A boat shop can easily do it for about $40 or less. It only takes a few minutes and it is absolutely crucial we know what your true rpms are. Knowing that, along with all the other info you have given, is undoubtably needed. Without that info everyone is shooting in the dark. Keep us updated!

 

[ba1335]

Re: First boat, rpms too high?

I think that's a good idea. I've also heard that adding some seafoam and getting a larger prop may help? If my ideal rpms are at 1200 rather than 6 or 800 can I conclude the tach is off? Or should I get it checked regardless?

 

[halfmoa]

Re: First boat, rpms too high?

If my ideal rpms are at 1200 rather than 6 or 800 can I conclude the tach is off? Or should I get it checked regardless?

what you NEED to do next is have your tach checked...That is the bottom line.

There's your answer right there. Non contact tachs can be found for about 10 bucks, a quarter of the price to get your tach checked with the same results. Get one and use it to check your engine revs and compare that to what your dash tach is reading. I'd agree with the others that've said there's no way that 4cyl is turning that fast on a load. Not to mention that it's still in one piece. Then again...maybe so. That's why you need to get the revs independantly checked.

 

[steelespike]

Re: First boat, rpms too high?

The idle speed on the tach doesn't mean much.There's no way a healthy prop would allow 6000 rpm.
At about 200 rpm per inch you would have to drop 5 to 6" of pitch to get to 4800.
A 13 or 14" prop is more likely to be used on a very heavy or hard to push boat
like a pontoon.

 

[QC]

Re: First boat, rpms too high?

Hey spike,

Just so this doesn't get messed up, and I know you know, but maybe your noodle is fried today. He would need to go up 5 to 6" So we're talking a 25" inch to drag down.

We haven't talked about a spun hub. I still think Tach because that poor 3.0 would probably splatter that high, but some have reported some pretty high speeds with a spun hub. Personally I don't buy it, but needs to be considered.