Not getting WOT RPM's

[Rlubbers6]

I have a 16ft Sea Nymph with a 1989 Johnson 30hp, model number J30ELCED. The guy I bought it from said he had the boat up to 28mph on the fishing graph. As for weight on the boat, I have one Deep cycle battery in the bow along with a bow mount trolling motor, then tackle boxes and fishing poles that are always on the boat. When I am on the boat alone or with just one other person I can get to 22mph but the RPM's only will go to 4100 (this motors max should be 5500.) Once I get 3-4 people on it the rpm's won't even get up to 4100. I have tried trimming it up farther and down farther but it doesn't seem to help. When I have 3 or 4 people total on the boat it will hardly get onto plane.

It has a 10X15 prop right now. Does this seem like a prop/trim issue or someone told me it could also be that the Carb needs to be cleaned out. I would be completely fine with it if it would go onto plane with more people on it. The only other thing I can think of that might affect it is the piece of the lower unit that goes lower then the prop.... Don't have a clue how else to explain that, but it is cracked slightly and bent a little bit, maybe that does something to it also?? I can upload a photo if that will help.

Thanks

 

[pootnic]

Re: Not getting WOT RPM's

Is your Sea Nymph a jon boat style or more of a semi V?
Even without looking at your numbers I thought the 15 pitch was alittle big for that combination(just from experiences)
With a 30hp on a 16'er I'd think around a 12-13 pitch,maybe even an 11 with a heavy load.
Now after looking at your numbers,a 13 isn't even going to get you the proper rpm's.
What type of tach are you using,and what are you using for speed?
If your tach is right,I wouldn't use the outboard to much,your lugging it pretty good.

If he was going 28mph at 5500rpm the boat slip would be around 22(if gear ratio is 2.15:1)
The numbers you give,the slippage is 19 but your low on the recommended rpm range.
I could be the motor but I think the pitch is alittle high...

 

[Rlubbers6]

Re: Not getting WOT RPM's

It is the semi v style. The tach I am using is just the one that I am assuming came along with the boat and motor? The console looks like it came with the boat stock including the gauges. Is there another method of seeing the rpms that is more accurate?

As for speed I am just using the fishing graph because the speedo starts at 10mph so it's hard to tell the speed accurately.

I didn't ask him what rpms he was at going 28mph. Now after reading anything about outboard motors I probably should have asked those kind of questions.

 

[steelespike]

Re: Not getting WOT RPM's

Pooptnic has you on the right track A 15" prop is the highest pitch listed here for a 89 30 hp.
very hard to push a load with a high pitch. As he suggests i think the 12" is a good starting point
considering you carry up to 4 people.
My info says max rpm is 5800 if it can turn the 12 up to 5800 it will get around 27 mph.
If the 12 lets it rev too much just throttle back a little. It wil;l give you plenty of peppy performance with a load while you decide if you need a change.
Before making a change you might want to be sure they setup is right.
the anti vent plate (just above the prop)should be about even with the bottom of the transom.
Be sure the throttle opens all the way.Is the bottom clean and smooth?
A gps is best for speed accuracy. Some cells have a gps app.