WOT not even close to where is should be.

[skongolf]

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.

 

[trendsetter240]

Re: WOT not even close to where is should be.

Nope. Either your tach or your speedo is out big time.

There is no way that setup can be moving at 40mph at 2000 rpm.

Check out your gauges before looking at props.

 

[skongolf]

Re: WOT not even close to where is should be.

40 mph I can see. 2000rpm, no way!!! It idles at 700. What do I need to check? Or how do I check?

 

[trendsetter240]

Re: WOT not even close to where is should be.

I'm going to say that tach is bad. If idle is 700rpm and you're going 40mph at 2000rpm then...

Take if into an automotive shop and they should be able to test it for you. Call ahead to be sure.

 

[steelespike]

Re: WOT not even close to where is should be.

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.

 

[Silvertip]

Re: WOT not even close to where is should be.

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.

 

[skongolf]

Re: WOT not even close to where is should be.

If i need to get a new tach, what kind would i need. Did a google search and didnt find much at all.

 

[Silvertip]

Re: WOT not even close to where is should be.

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.

http://www.iboats.com/Boat_Tachometers/dm/*******.731405391--**********.952262525--view_id.248010

 

[skongolf]

Re: WOT not even close to where is should be.

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?

 

[steelespike]

Re: WOT not even close to where is should be.

It is usually suggested you rotate the switch several times to try to clean the switch contacts.

 

[Silvertip]

Re: WOT not even close to where is should be.

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!"

 

[skongolf]

Re: WOT not even close to where is should be.

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.

 

[steelespike]

Re: WOT not even close to where is should be.

I know nothing about the switch itself.If you can feel a detent at each position I would rotate back and forth creating a sort of scrubbing effect.