Top end limit of 60 EFI Mercury Jet

[RadarJet]

Ran into an interesting problem this weekend on the river. I was barely able to get up on plane going upstream, even when pushing the engine nearly up to 6,000 rpm. I shut it down and checked for blockages and debris, which there were none, but noticed when turned off, the tach still read 1,500. When I started it back up, even at idle it read about 1,400 rpm. Since this is an EFI motor, I'm not sure how to adjust the idle, or even if I can. I'm pretty familiar with motors, and just by listening, it was not idling over 800 rpm. Could the Teleflex tach that is installed on this boat (new to me) just be off in calibration, and I was really only pushing 4,500 rpm instead of 6,000 rpm? For a few seconds I did give it some extra throttle and trimmed up a bit, and it pushed easily to about 6,300, sounded great and gained a ton of speed. Is this motor self protected from over rev? Should I not be able to over run this motor with the jet?
Thanks for the help.

2002 Mercury 4-stroke EFI- OT504907
2002 1652 Alweld Jet. 2- batteries, 14 gallons fuel, TM, and wife and child on board.

 

[onthewater102]

You were able to hit 25mph+ though? If so that rules out spun hub...

 

[eli2]

A couple questions, when you say new to you, is this the first time you have had the boat out, or have you had it out before and this is the first time you encountered any issues? Also, all the tachs I have ever had read zero when the engine wasn't running. My Merc generally tops out around 5200 or so, I heard same size Yamahas rev a bit higher due to a smaller pump, but not sure. As for the trimming up, it is a good way to pick up a little speed once up on plane, if you have better performance all the time with up your motor may be hung
to low. Your boat should plane pretty quickly and scoot along around 25 with said load. If the boat is new to you, I say trust your instincts with the way the engine sounds and take a look at how the motor hangs in the back. An acquaintance of mine has the same boat and had to install a jack plate to get the desired performance.

 

[dhoganjr]

There should be an adjustment on the back of the tach, it may not be set up correctly. They are designed to be used with most engines, but I don't know which setting it is for 4-stroke, maybe someone else can help out there, if not call a dealer service department you trust. Tach could be bad, could have a bad connection. When I had the Teleflex analog tach on mine when the engine was shut off it would read what rpm it was at when it shut down. Soon as I turned the key it would drop to 0.

EFI is all ecm controlled, no adjustments that I know of. It should also have a rev limiter to protect from over rev.

(Don't know your history with jets, if you're new to them maybe this will help.)
When you take off, starting out of the hole have the engine trimmed down, when you start gaining speed and the bow starts coming down start trimming up. Once on plane the engine should be close to level, you'll know when you hit the sweet spot. When it starts to porpoise or if it cavitates bump the trim down a few times till it stops. If you keep it trimmed under on plane the bow is plowing water and the shoe is dragging slowing you down.

Also as eli2 mentioned check the mounting height. Do this by taking a straight edge (yardstick, board, angle, or whatever you have handy) and place it level on the bottom of the hull and extend it out to the shoe. It should hit the shoe somewhere between the leading edge and the pin that holds the grates in with the engine trimmed down. Also check throughout the trim range until engine is level. If the leading edge of the shoe drops below the straight edge then its dragging, slowing you down and probably has a lot of backsplash at the transom. If this is the case it needs raised.

Good luck, hope this helps!!!

 

[RadarJet]

Really appreciate the help here. I just took ownership of the boat, but it has been in the family for the last 8 years. As far as I know, the tach has always been like that. What got me thinking about it is when I bump the throttle the tach jumps to 3,000 rpm but the boat hardly moves. I've got to push it to 4,000 rpm to break 5mph, and it feels like a barge then. We were traveling about 25 to 26 mph last weekend with the tach reading 6,000, so I doubt a key is broken.

The bottom front of the jet foot is about 1/4" higher than the bottom of the hull when trimmed all the way up. There are two holes remaining, so I'll move it up and see how it goes then.

Ill clean the electrical connections tonight and check the rest of the electrical while I'm at it.

My last question would be is it harmful to push the throttle all the way up to touch the rev limiter to just see where it is at, or should I stay clear of there?

Thanks again!

 

[dhoganjr]

If it's a 1/4" higher the height should be ok.

How does the impeller look, has it been dressed (sharpened) recently and is it shimmed correctly. These 2 will make a big difference in getting on plane and top end speed. Also check the nozzle and make sure there are no rocks lodged between the exhaust tube and nozzle.

I wouldn't intentionally try to hit the rev limiter, these computer controlled engines can go into limp-in mode if it is over-revved too many times. If it does this it will only turn about 2000 rpm's to protect the engine until you get it serviced.

Have the fuel lines been replaced, if not the liners are more than likely ate up from ethanol and it will break up clogging filters, fuel pumps, etc. They will need to be replaced with the newer ethanol resistant lines.

If any of this don't help, we'll go from there.

 

[eli2]

The motor height should be check with the motor trimmed all the way down as dhoganjr said. If it is 1/4 higher when trimmed all the up then it must be way low when trimmed all the way down.

 

[dhoganjr]

I missed that line where he said it was trimmed all the way up, if that is the case the measurements do need to be taken with the engine trimmed down or tucked under.

 

[RadarJet]

Man, a person can really sound uneducated when they don't proofread. I meant that when trimmed DOWN the bottom front of the foot is 1/4" higher than the bottom of the boat. When trimmed to horizontal; the back of the foot is level with the bottom of the hull- so I think it is reasonably good there. I will be updating the fuel lines, as I am shocked that there are no leaks from this no-name line that is starting to crumble. However, the fuel filter looked pristine when I first inspected it.
I have just serviced the impeller, liner, and water pump about 4 running hours ago, so they are all good. I am much more careful about running shallow with this boat than my old 14' jon.

There was one sketchy connection on the back of the tach, so I repaired that at re-torqued all others.
We will see how it runs & reads this weekend. Thanks for the advise.

 

[eli2]

No problem. The motor looks good with the pic you sent, so if were me I would go with the fuel lines like dhoganjr said. Good luck.

 

[Lil' Blue Rude]

Could be how the impeller was sharpened. I've seen boats that couldn't hardly plane after being sharpened incorrectly. I've always sharpened on top of the leading edge and outboard jets claims you need to sharpen on the bottom of the leading edge. People sharpen them both ways but that's the method that's worked best for me. Look at a new stainless from mercury and look at a aluminum from outboard jets and compare the leading edge, then see which one performs better. The stainless should hook up better. It's because of the way the leading edge is on the stainless. It's hard to find much info on this about outboard jets but if you look up inboard impellers they talk about the leading edge pitch and all that stuff and explain what effects what.

 

[RadarJet]

You raise an interesting point about the impeller sharpening side. While I still think that the tach is not reading correctly, the grind on the auger could add to the problems too. As an engineer by trade, I always try to follow the manual on manufactured parts. I did sharpen this auger per the Outboard Jets manual, filing off the bottom edge. Funny thing is that it does not feel any quicker than when I got it, with a fully dulled auger that had zero taper (grind) left to it. I'll do the top edge next time and see how it performs.
I did sharpen the top edge of my 25 Mariner jet and it appeared to work a lot better than the factory grind. I do feel like sharpening the top side would work to force more water into the pump than the bottom side.

 

[Lil' Blue Rude]

Yeah when you sharpen on the top it brings the leading edge down a little bit, that increases the pitch a little on the leading edge causing it to bite better. At least that what I can figure, kind of one of those to each their own kind of things.

 

[RadarJet]

To wrap this thread up it turns out the tach issues were all in the wiring. Found some pretty sketchy wiring connections under the console, and a loose wire nut on the tach- all with some corrosion. Cleaned it all up and added some dielectric grease- and it works just like new now. Shows idle at 800 rpm, and motor maxes out at 5,500 rpm at full throttle. Ran it over some flooded river water this weekend with 6" chop and it never missed a beat or cavitated. The only thing I had to worry about were those jumping carp.

 

[smackdaddy53]

Nice! You have any video?

 

[dhoganjr]

Glad to hear you got it figured out.