I have been wanting to get a new prop for my 97 Maxum SFL 2000 so today I thought I would check my WOT range. Right now I have a 14 1/2 x 18 3 blade aluminum prop on there. The specs say for the Mercruiser 5.7 to have a range of 4400 to 4800 RPMs at WOT.
So I start out my test with my 2 kids, my GF and 2 dogs in the boat with the trim all the way down so I would say about maybe 450-500 lbs on the boat with people and an ice chest. The lake was calm and no wind an on the first run I got 2000RPM and 40 mph. 2000 rpm?? so i trimmed up a little and tried again. 2100 and 38 mph.
Something seems way off!! I dont think changing props will get me up to 4000 rpms. I want to get a 4 blade aluminum since we do alot of wakeboarding and I can't afford a stainless 4 blade right now.
Just looking for some thoughts or recommendations.
Yup your tach is bad. I assuime your Maxum is a 20 footer if its not a cruiser type hull I think its a little slow but lets get the tach settled first.
Connect a shop tach and compare the two. But I agree with the others. The setting on the back of the tach is probably incorrect. There is typically a small adjustment on the back. Note its "current" setting then rotate the adjustment back and forth several times to "clean" the contacts. Set it back to the original setting and make a run. If it still reads 2000 rpm the adjustment was not just dirty. Next, post what settings the tach has. It should be set for an 8 cylinder engine when in fact it might be set for a 4 cylinder which would result in the reading being 1/2 of what the 8 should be. Hence you would be at 4000.
Marine Tachs are very generic -- meaning nearly one size fits all. But why not troubleshoot what you have. Throwing parts at a problem is not wise. You very often wind up with the same problem. But if you do need a new tach get it right here on iBoats. After all, they sponsor this very nice forum. Click below.
Ok I checked the back of the tach and it was set to 4. Took a scredriver and turned the arrow to 8. Turned really easy and actually went past 8, but I set it to 8. Got to the lake and did the test and the RPMS went to 2500 WOT. I have a feeling something is wrong with the adjustment screw as it moved really easy, almost too easy and went past 8. I just feel like there should have been some kind of resistance. I also checked and adjusted all connections to the tach. My next question is, Is there an easy way to get it out through the front of the dash or do I have to do it from underneath? I am 6'5" and there is not alot of room under there at all! Just looking for some suggestions. I was basically given the recommendation of a 4 blade 14 1/4" x 17 prop from a prop shop. Any thoughts?
The tach is held into the console by a "U-shaped" bracket. Remove the two nuts that secure the bracket and pull the tach out the front. Disconnect the wires NOTING WHERE EACH ONE GOES! i'm not swearing at you. I'm just getting your attention. Folks tend to unhook wires thinking they can remember where they go. Six weeks later when they finally get around to the repair they no longer remember and we get the typical question - "where do these wires go!"
Ok, I will try and adjust again tomorrow since we are going to the lake Sunday. Best to rotate clockwise or counter clockwise? Not real happy about having to get my hands to the 2 nuts that hold the tach in Hopefully adjusting the screw works.
WOT not even close to where is should be.
Hopefully adjusting the screw works.
Linear Mode
