My max RPM is only 4000???

[hogginhank]

Well I ran my boat after the fuel pump conversion and it really runs good, BUT the RPM's still don't go above 4000. The compresion is good in all 3 cylinders, it idles perfect and jumps out of the water and I'm at 32 mph and 4000 rpm's without any bogging or anything.

I replaced all the fuel lines with marine grade lines, cleaned out the primer solenoid and everything that has to do with the fuel system so I don't think it is a fuel issue.

I read a LOT of my service manual and some of it is understandable and some of it isn't

My question is can this be a timing issue?? Or a link and sink issue(I'm not really sure how this is done even though I read about it in my manual)

Oh and I had a 19 pitch prop on the motor and switched to my 15 pitch prop and the RPM's still stayed the same..Right about 4050 at the most. This is the same level of RPM's that my boat was running at before the fuel pump took a dump??

Any advice on what to check next on my own before I have to take it in to the boat shop here. My neighbor is a mechanic so he is going to check the timing for me but after that I'm not sure what to do next to trouble shoot the low RPM problem. The motor really seems to be running great except for the rpm's stopping at 4000??

It is a 1995 3 cylinder 50 HP evinrude 2 stroke

 

[wilde1j]

Re: My max RPM is only 4000???

Had the motor ever turned 5500 to 6000 RPM?

 

[hogginhank]

Re: My max RPM is only 4000???

When I got the boat the jack plate was all the way up and the prop was barely in the water and would cavitate a little when you turned the boat left or right when on plane(it does have an anti-cavitation plate on the lower unit). It only got to 5100 when it was all the way up. And it only went 29 mph with the 19 pitch prop. I had to take the carbs off and clean them and after that and moving the jack plate down the rpm's would stay around 4500 WOT and the motor would still seem to run good. It would run at about 35 mph and 4500 rpm's with the 19 pitch prop after I lowered the jack plate .

That was all about a year ago. I have been running it a couple times a month for the last number of months and now just recently rebuilt the carbs, new fuel pump and all fuel lines have been replaced as well. New plugs that are gapped per the manual. Fuel tank has all new marine grade fuel line and there are no air leaks and the uplift filter is clean. I have done a lot of back tracking and delt with the fuel issues and there are no issues with any of the fuel getting to the motor. I'm hoping it is a timing issue or something. Especially since when I change my prop 4 pitches the RPM's still don't change??

 

[Chinewalker]

Re: My max RPM is only 4000???

If you switched from a 19 to a 15 and nothing changed in your tach reading, then I would say your issue is with the tach, not the motor. If this is a 3-cylinder 60 or 70, then a 19 is a lot of pitch for one of them unless you're running a really light performance hull. I run a 17" on my 75hp triple/15-footer and it spins around 5800 RPM at WOT.

 

[bkwapisz]

Re: My max RPM is only 4000???

Did you try trimming the motor up a little? I know on my big SeaRay I have to start with the drives down to dig out of the hole, and then I trim them up once on plane and have to actually back off the throttle a little as it speeds up and the RPM's increase as the I trim it up towards level. Bottom line is that if the trim is down (bow down) it will strain the motor and the rpms and mph won't be there.


Just a thought FWIW.

 

[SKEETR]

Re: My max RPM is only 4000???

Check the carb butterflies with the engine off. At full throttle are they fully open?

 

[hogginhank]

Re: My max RPM is only 4000???

yep the butterflies are open and all linked at the same closing/opening point. I tested my tach with my neighbors portable digital tach thing and actually adjusted my tach a while back so I know it is working at lower rpm's..Maybe it is not reading properly at the higher rpm's?? The motor doesn't sound very rapped out at all so I'm pretty sure that it is not reaching the full WOT rpm that it should.

 

[hogginhank]

Re: My max RPM is only 4000???

If you switched from a 19 to a 15 and nothing changed in your tach reading, then I would say your issue is with the tach, not the motor. If this is a 3-cylinder 60 or 70, then a 19 is a lot of pitch for one of them unless you're running a really light performance hull. I run a 17" on my 75hp triple/15-footer and it spins around 5800 RPM at WOT.

The boat hull is a 1656 WeldCraft aluminum jon boat hull with a center console and not much else so it is pretty light. I got the higher rpm's when I first got the "used" boat so I am really at a loss trying to figure out why I can't even get to 4500 rpm's even after everything I fixed/replaced is all 100 proof and done right, and better than before??? I sure wish I knew what was going on??

 

[SKEETR]

Re: My max RPM is only 4000???

Try timing it following the Joe Reeves method found here in the FAQ forum.

 

[kenmyfam]

Re: My max RPM is only 4000???

19 inch pitch is huge for that motor in my opinion. You should see a difference with the 15 inch though. How about a photo of the lower unit and the back of the boat ??? (side on)

 

[joey maneri]

Re: My max RPM is only 4000???

is your boat kept in thr water? maybe the bottom is getting dirty.

 

[hogginhank]

Re: My max RPM is only 4000???

I'll check out the timing tip from the faq's thread. No the boat doesn't sit in the water and the lower unit is clean as well as the hull.

Question?? Can the timing be off enough to affect the WOT RPM's that much and it still run good?? Thanks again for all the input..Hank

 

[SKEETR]

Re: My max RPM is only 4000???

Timing is huge when it comes to max rpm. If yours is off it is probably in the safe zone. What you don't want to do is set it too advanced or you can start melting pistons. The wot timing adjustment will not affect your idle in the least.

 

[hogginhank]

Re: My max RPM is only 4000???

Timing is huge when it comes to max rpm. If yours is off it is probably in the safe zone. What you don't want to do is set it too advanced or you can start melting pistons. The wot timing adjustment will not affect your idle in the least.

thats good info..

2 questions for you on that note:

Can my timing retard my WOT rpm's 1500 rpm's ??

Will the "Reeves" timing method do what you are syaing and melt my pistons or is it safe to try this setting??

Thanks in advance for any further info..I am going to check the timing tomorrow when I get off of shift to see what I come up with. I will let ya'll know..Adios' for now..Hank

 

[SKEETR]

Re: My max RPM is only 4000???

It is worth trying. You don't even have to run the engine to check the timing so there is no need to fear. What is important is you have the correct btdc timing number for your motor. As long as you follow the instructions by subtracting 4 degrees from your mark you should be fine.

Will it get you 1500 rpm? I just can't say for sure but it is free to check it out. There is still a possibility you are one hole down. But with your description of how well it runs I have not suggested it as a posibility yet.
My v4 ran pretty damn good on three cylinders, not sure if a 3 cyl would run well on two though.

 

[hogginhank]

Re: My max RPM is only 4000???

It is worth trying. You don't even have to run the engine to check the timing so there is no need to fear. What is important is you have the correct btdc timing number for your motor. As long as you follow the instructions by subtracting 4 degrees from your mark you should be fine.

Will it get you 1500 rpm? I just can't say for sure but it is free to check it out. There is still a possibility you are one hole down. But with your description of how well it runs I have not suggested it as a posibility yet.
My v4 ran pretty damn good on three cylinders, not sure if a 3 cyl would run well on two though.

Sounds good. I'm not sure what the btdc stands for(something-timing-something-something?) but I'm sure it's in the service manual I just got from iboats last week so I will check out those pages again. I did read through the section on timing but since I am just a carb rebuilder / impeller replacing level motor mechanic(lol) I will get my mechanic neighbor to guide me through this part with my manual since he has rebuilt/fixed all of my other neighbors outboards for them. You mention "One Hole Down"..Is this refering to the setting on the timing number it's currently at? Thanks again for all your time and expertise on this issue..Hank

 

[SKEETR]

Re: My max RPM is only 4000???

btdc=before top dead center

By a hole down, I am suggesting that one cylinder may not be firing. At least at high rpm. Usually a failing coil or power pack. Kinda thought my v4 comparison would clear that up
You can check that next once you have established your timing is correct.

 

[CharlieB]

Re: My max RPM is only 4000???

I would be very suspicious of your tach.

A four inch change in prop pitch should have a noticable change in WOT RPM.

To an untrained ear it may not be appearant, but the tach should show the change.

 

[hogginhank]

Re: My max RPM is only 4000???

btdc=before top dead center

By a hole down, I am suggesting that one cylinder may not be firing. At least at high rpm. Usually a failing coil or power pack. Kinda thought my v4 comparison would clear that up
You can check that next once you have established your timing is correct.

I am by no means a mechanic though I have worked on a lot of 25 hp and smaller outboards when I worked at a marina for a few years right out of high school. With that said I tried to listen for a difference in engine sound/rpm at WOT with the 19 and 15 pitch prop and it really didn't sound any different to me. The rpm went from 4000 to maybe 4050 when I put the 15 on it?

What I need to do tomorrow is check the WOT rpm's on my tach with my neighbors portable tach reader "Again" since the last time I checked it was 10 months ago when I initially cleaned out the carbs after they had sat for about 10 months. My tach might have fallen back down in rpms?? It does idle at about 1000 on muffs and about 850 in the water??

Question? Wouldn't I hear if I was one hole down at WOT since I only have 3 cylinders??

Thanks again for all the quick replies..

I just got through reading all the stuff on link and sink and I have that mostly taken care of. My engine idles really well at right between 2.5 and 2.75 turns out on the rich/lean screw and there is no sputter or bogging when I take of or get to WOT so I won't focus too much on that right now. I will have him check my idle timing just to be sure it is within normal limits so I can check that "Check Box" on all of my rule outs..I also read the timing and spark advance and all of those pages (2 times) and I have a better understanding of it so when I assist my neighbor I will know kind of what he is doing. I will keep ya'll posted and I should have a few more question in the next few days..You folks are really awesome..Adios' for now..

By the way, where can I get a tach for my boat that won't break the bank??

 

[CharlieB]

Re: My max RPM is only 4000???

The 'One hole down' comment is addressing the engine mounting on the boat. Raising or lowering the engine by one hole can have an affect on Holeshot as well as WOT RPM.

I wouldn't go there yet unless you have had the motor off and changed the hight when reinstalling.

If the motor performed when you first got it but now does not then it is an issue yet to be determined.

We just haven't figured out what, yet.

There some great minds here, keep asking questions, and posting answers to our questions, we will get it figured out.