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PostPosted: 11 Jul 2016, 13:30 

Joined: 14 Mar 2010, 21:30
Posts: 25
I've got a Lowe 1655 with a 60/40 Jet. I'm showing a WOT of 4800 on the tach which seems on the low side. I'm getting around 24-26 MPH which also seems a bit low. River was way up and moving fast last weekend and I got it up to 28.5 downstream, but still never turned more than 4800. Does this seem correct? Dealer claims it's because of the heat. I'm not buying that.

-Chris



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PostPosted: 14 Jul 2016, 23:21 
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Joined: 26 Sep 2015, 01:16
Posts: 126
Location: Washington, MO
There may be a connection to the heat and high humidity that you're experiencing but your 4800 RPM is not that far off what you should normally expect which should be around 5000 RPM. You could drive yourself crazy (and broke) trying to squeek that last 100-200 RPM out of the motor or you can check obvious things and then just let it go. You might find some non-ethanol, premium and also run an external fuel/water filter but it's not like you're operating a race boat with that 40HP 4 stroke jet.



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Current Craft: Lowe 1448 Big Jon, all aluminum transom, decks, console w/ Yamaha 40/30.
Previous: Cajun 185 w/150 Johnson, Tracker TX17 w/60 Mariner, 24' Pontoon w/60 Merc, Ozark Tri Hull F/S w/120 Evinrude, 16' Lowe Olympic Jon w/ 40 Mariner, 12' Lowe w/ 4.5 Merc, Coleman Scanoe, Ouachita alum canoe
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PostPosted: 15 Jul 2016, 08:36 
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Joined: 20 Jun 2012, 11:40
Posts: 1947
Location: Falling Waters, WV
Just for reference I get around 5200-5300 with my Johnson 50/35 on a 1648MV. When loaded properly it tops out about 26-28 down river. My boat is pretty light though with a probably .080" hull or even less. It does run a bit better in the cooler times of year, but nothing significant and no difference in RPM's that I've noticed. IIRC, I did loose a few RPM's when I switched from an aluminum to stainless impeller. What does your manual say for WOT RPM's? Mine is supposed to fall between 4500-5500. One simple thing to check is your reverse gate. Make sure it is fully locked down when you throttle past neutral. If it doesn't that could knock your RPM's down, although I'd imagine more significant than 4800.



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BigTerp's Tracker Sportsman 16' build-------> viewtopic.php?f=21&t=26774
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PostPosted: 15 Jul 2016, 09:14 

Joined: 14 Mar 2010, 21:30
Posts: 25
Manual says 5500-6000, Outboard Jets says 5300+, Mercury is still trying to figure out what it's supposed to be. The dealer told me they ran an identical boat to mine at 4850 RPM's with a top speed of 27 which is right about what I am getting. The motor produces top HP at 5k, I don't see why Merc would have put that motor out not turning at least 5. I did find out the impeller is stainless and Mercury provides it. I also found out they back cut the trailing edge of the impeller to get more RPM's. Mercury is supposed to call me back once they talk to a product manager. I'll send an update once I hear back. It may be what it is, but I still feel that motor should open up a touch more.



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PostPosted: 15 Jul 2016, 12:48 

Joined: 02 Mar 2012, 02:24
Posts: 94
Location: St Louis, Mo
You may have one of the old style impellers made for the two stroke, they found that the four stroke was unable to spin it to a reasonable rpm and had to cut them back. This thread has some good info on page 2.

http://www.tinboats.net/forum/viewtopic ... 0&start=15


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PostPosted: 18 Jul 2016, 07:09 

Joined: 14 Mar 2010, 21:30
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Interesting you say that. I spoke to the third person at Mercury and explained I needed to talk to someone very familiar with that motor. This person agreed that the RPM's were low, and talked to a product specialist who also agreed they were low. His fix was to order a new Merc Impeller, that most likely the one that is on the boat was an older model that had not been modified for the four-stroke. More to come...



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PostPosted: 18 Jul 2016, 20:39 
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Joined: 02 Jun 2015, 09:56
Posts: 476
Location: Bedford Indiana
If you get one of the new impellers I would be interested in your old one I have a two stroke 60/40 and would rather have the old style impeller. I can pm you my contact info if you'd get the new one and find out you do have the old style impeller and want to sell it.


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PostPosted: 19 Jul 2016, 09:24 

Joined: 14 Mar 2010, 21:30
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I'm pretty positive that Mercury is going to want this one back. I'll see what happens. It's a brand new boat/motor and this would be Warranty.



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PostPosted: 26 Jul 2016, 14:57 
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Joined: 02 Jun 2015, 09:56
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Location: Bedford Indiana
If it's possible for you to keep it try to if you don't mind.


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PostPosted: 20 Oct 2016, 23:32 
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Joined: 08 Apr 2014, 07:59
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Location: SouthWest Virginia
MrTotty wrote:
Interesting you say that. I spoke to the third person at Mercury and explained I needed to talk to someone very familiar with that motor. This person agreed that the RPM's were low, and talked to a product specialist who also agreed they were low. His fix was to order a new Merc Impeller, that most likely the one that is on the boat was an older model that had not been modified for the four-stroke. More to come...


Any update on your motor's performance with a new impeller? I ask because I'm going through the same hassle that you have had. I also have a Lowe 1655. About a month ago I replaced my 2005 Mercury 2 stroke 40 Jet with a new Mercury 4 stroke 40 Jet. When I got a chance to get the boat with the new motor out on the water, max RPM at WOT was 4500 and top speed was around 22 mph. It would just barely get on plane. I took it back to the dealer. After about a week and a visit by a Mercury Tech Rep to check it out, they finally gave up on trying to find the problem with the motor and shipped another one from the factory and put it on my boat. The new replacement still doesn't run up to the RPM specified which is around 5500-6000. At best it runs around 5200 at WOT, usually less and the top speed is only around 26 mph on still water. The dealer says that the motor will run at a higher RPM after it is completely broken in. I have doubts about this.

I replaced my old 2 stroke because the powerhead needed rebuilding and I didn't want to put a lot of money into it. I'm beginning to think I would have been better off going with the rebuild. Back when it was running right, the 2 stroke ran 5250 RPM at WOT and got around 28 MPH top speed.


Last edited by LarryMc on 23 Oct 2016, 17:42, edited 1 time in total.


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PostPosted: 21 Oct 2016, 06:36 

Joined: 14 Mar 2010, 21:30
Posts: 25
The issue with your first motor was most likely the impeller. The impeller on mine from the factory was as I thought an uncut 60HP 2 stroke impeller. Mercury backcuts the 4 stroke version to get more RPM's out of the motor. Your speed is dead on what mine is as an average. I get between 5200 and 5400 now which gained me 2 MPH. I'm still not happy with the performance and I'm looking into going back to a prop on the boat. I do really like the boat. I think that boat is way underpowered with a 40 Jet and would be much happier with the 65 or 80 (90/115) motor. I'm trying to figure out what the performance specs would be with the 60 with a prop. I'm going to guess high 30's maybe even low 40's.



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PostPosted: 21 Oct 2016, 08:06 
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Joined: 02 Jun 2015, 09:56
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Location: Bedford Indiana
MrTotty wrote:
The issue with your first motor was most likely the impeller. The impeller on mine from the factory was as I thought an uncut 60HP 2 stroke impeller. Mercury backcuts the 4 stroke version to get more RPM's out of the motor. Your speed is dead on what mine is as an average. I get between 5200 and 5400 now which gained me 2 MPH. I'm still not happy with the performance and I'm looking into going back to a prop on the boat. I do really like the boat. I think that boat is way underpowered with a 40 Jet and would be much happier with the 65 or 80 (90/115) motor. I'm trying to figure out what the performance specs would be with the 60 with a prop. I'm going to guess high 30's maybe even low 40's.


Did mercury take your old impeller? I'd still be interested in it, as I have a two stroke and hell will have to about freeze over before I run four stroke outboard with a computer on it.

LarryMc wrote:
MrTotty wrote:
Interesting you say that. I spoke to the third person at Mercury and explained I needed to talk to someone very familiar with that motor. This person agreed that the RPM's were low, and talked to a product specialist who also agreed they were low. His fix was to order a new Merc Impeller, that most likely the one that is on the boat was an older model that had not been modified for the four-stroke. More to come...


Any update on your motor's performance with a new impeller? I ask because I'm going through the same hassle that you have had. I also have a Lowe 1655. About a month ago I replaced my 2005 2 stroke 40 Jet with a new Mercury 4 stroke 40 Jet. When I got a chance to get the boat with the new motor out on the water, max RPM at WOT was 4500 and top speed was around 22 mph. It would just barely get on plane. I took it back to the dealer. After about a week and a visit by a Mercury Tech Rep to check it out, they finally gave up on trying to find the problem with the motor and shipped another one from the factory and put it on my boat. The new replacement still doesn't run up to the RPM specified which is around 5500-6000. At best it runs around 5200 at WOT, usually less and the top speed is only around 26 mph on still water. The dealer says that the motor will run at a higher RPM after it is completely broken in. I have doubts about this.

I replaced my old 2 stroke because the powerhead needed rebuilding and I didn't want to put a lot of money into it. I'm beginning to think I would have been better off going with the rebuild. Back when it was running right, the 2 stroke ran 5250 RPM at WOT and got around 28 MPH top speed.


You should have kept that two stroke a good clean one with a propperly rebuilt power head, with some minors mods is will walk the dog around the four choke, and is worth about the same as a used four stroke. But I'm obviously biased to two strokes, and in jets the 3 cyl omc two strokes were the best.


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PostPosted: 21 Oct 2016, 08:22 
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Joined: 08 Apr 2014, 07:59
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Location: SouthWest Virginia
MrTotty wrote:
The issue with your first motor was most likely the impeller. The impeller on mine from the factory was as I thought an uncut 60HP 2 stroke impeller. Mercury backcuts the 4 stroke version to get more RPM's out of the motor. Your speed is dead on what mine is as an average. I get between 5200 and 5400 now which gained me 2 MPH. I'm still not happy with the performance and I'm looking into going back to a prop on the boat. I do really like the boat. I think that boat is way underpowered with a 40 Jet and would be much happier with the 65 or 80 (90/115) motor. I'm trying to figure out what the performance specs would be with the 60 with a prop. I'm going to guess high 30's maybe even low 40's.


I think you are right about the impeller being the problem with the first motor. It had a manufacturers tag on it with "15" on it. I assume that means it was made in 2015. The replacement has a "16" on the tag. Seems strange that even the Mercury rep couldn't figure out what was wrong with the first motor. Like you, I'm still not happy with the performance of the 4 stroke 40 jet on this boat. But I guess I'll live with it. With the rivers I fish, a prop is not an option and I really don't want to put a 65 jet on it.

I'm going to pull the intake off of the jet lower today and check out the impeller and see what it looks like. I've never seen a backcut impeller. Is the difference between the old type and the new type obvious?

handyandy, I still have the 2 stroke. Depending on how things go with the 4 stroke, I may have the powerhead rebuilt and put it back on my boat.



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PostPosted: 21 Oct 2016, 08:37 

Joined: 14 Mar 2010, 21:30
Posts: 25
The year of the motor should not matter however, did you ever take the impeller out? If you did you would clearly notice the top end of had some shiny grind marks where metal was ground off. It's something you would not be able to miss. Here are pics of each. the shiny one is the right one for four stroke.

IMG_3767.JPG


IMG_3766.JPG



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PostPosted: 21 Oct 2016, 08:44 
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Joined: 08 Apr 2014, 07:59
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Location: SouthWest Virginia
Thanks, appreciate the photos. I haven't taken the impeller off yet. Plan to do it today. The dealer's mechanic took the impeller off the first motor and checked the numbers and said it was the correct impeller, but I didn't look at it. From what I've read online, Mercury didn't change the part numbers when they changed the impeller design, so I don't actually know which type was on the first motor.



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