Nissan NS40C mismatched prop???

[Jeffress77]

Last summer we bought this motor for our boat and got everything all hooked up and setup for a water test, and when we opened up the throttle, the motor "sounded" like it was running at full RPM, but without a tach. I don't know for sure. The front of the boat came up fast, but the boat had hardly any acceleration. It just trudged through the water at high RPM with the front of the boat up in the air.

I went ahead and got the numbers from my motor.

It is an NS40C

and directly under the model number it reads "361A-1 67621"

The stamp on the engine reads "2WT70C86"


The propeller reads 10 1/4 X 12

I am not sure of the proper propeller for my application which will be on a 15.5" Ebbtide fiberglass boat on smaller lakes. The original owner said it was used for a pontoon boat, but that is all I know.

Let me know what you think about that setup, or if it is even matched correctly for any application.

 

[pvanv]

Re: Nissan NS40C mismatched prop???

You need a tach to select the correct prop. You also need to trim the motor correctly. You can d/l an owner's manual at http://www.nissanmarine.com/tech_talk/owners_manuals.html

 

[steelespike]

Re: Nissan NS40C mismatched prop???

Welcome.
My info indicates that while the 12" might be light for your boat it should plane easily rpm might
end up too high.Motor should be trimmed in(down) for hole shot.
Weight should be balanced neither too muc stern or bow.Some passengers to the bow for planing then back to more balanced. 40 hp is a little under powered but should plane easily with 2 aboard.
I would suspect the motor is at fault;throttle not opening all the way,missing a cylinder,
poor compression,poor fuel distribution.
Boat could have a problem sometimes the foam under the floor absorbs water adding a couple of hundred lbs right at the stern.
For the final prop selection you should have a tach both for motor health and performance.
Tach will help determine prop size and tell how well the change works.
The latest Tinytach will work on a number of applications

 

[Jeffress77]

Re: Nissan NS40C mismatched prop???

thank you for the info. I will look into it further

 

[steelespike]

Re: Nissan NS40C mismatched prop???

Please let us know your progress.

 

[Jeffress77]

Re: Nissan NS40C mismatched prop???

I bought the Tiny Tach 2 and it is a nightmare to get to work correctly. I set it up for 1 spark per rev. as per most 2 cycle engines.. then tried getting a reading with 3 or 4 wraps around the plug wire and changed the ground on 3 or 4 different places to make sure I had ground. The ONLY way that I can get a reading on the Tiny Tach is to hold the red wire in my hand AWAY from the plug wires. Once the red wire from the meter is OFF of the plug wires I can get a reading. If the red wire is almost touching the spark plug wire then the meter will read in between 1800-2000 rpm while jumping around in between the numbers...once the red wire is pulled slowly away, the rpm reading will decrease. All of these measures were taken with the motor flusher on the lower unit in my driveway.
The Nissan manual reads that idle RPM should be 950 with the clutch off. So if the meter is anywhere close I am 1000 RPM too high?!?!? I was recommended by many for this Tiny Tach, but it really seems like it is not designed very well. At first I was getting a reading of "U110" on the meter and then it was simply illuminating all of the display "1888888" and flickering. When I pulled the red wire away from the plug wires, it gave me a varied readout. What should I do?

 

[steelespike]

Re: Nissan NS40C mismatched prop???

Be sure you have followed all the procedures Be sure its not getting interference from other wires.
Perhaps you can get help direct from Tinytach. While there have been some minor glitches
To my knowledge yours is the first that refuses to work all together.
I would suspect your getting stray pulses from other wires.
I'm sure you could take the reading from any plug wire Perhaps a wire farthest removed from the others and wrapped farther from the plug.You'll need to get your ground from a bare spot with no paint on it.

 

[Jeffress77]

Re: Nissan NS40C mismatched prop???

Ok, well we tinkered around with the idle speed a bit, and got closer to 1200-1300 rpm on idle, but that was with the red wire for the tiny tach just barely touching.

We took her out on the water, and got a full wide open throttle reading of 6280-6300 RPM. Book says the WOT reading should be 5200-5700. The boat was making a great wake, at this RPM, but still trudging through the water at slow speed...(probably 10mph).

Since I am getting a reading close to 6300 RPM I assume that I will have to adjust the carb. somewhat to get desired RPM...but when we turned the idle down closer to 1000 rpm the engine will not stay running for more than a couple seconds. Not until we turn the idle to approx. 1300 will it stay running.

The meter is reading 400-500rpm higher than book value at idle and also 500-600 rpm high at full throttle on the water. Will this rule out a problem with the motor as far as accelleration and speed? Should I now focus on the prop? What should my next step be? thank you for your help
-Justin

 

[steelespike]

Re: Nissan NS40C mismatched prop???

Your Tinytach isn't working right.
I'm not aware what color wires do what All I know is the induction wire that wraps around the plug wire must be wrapped as described and must not be near any other wire.Be sure any other connections are clean and tight.Any readings your getting now have no value as near as I can tell.
You may have to return the tach if you can't get it to work when installed as directed.
The tach was more for getting a rpm reading once planed.
Lets check some things first Check that it is running on both cylinders.
Disconnect and ground one plug wire at a time and see if it runs.Pull each plug and note the condition.Should be brownish. And both should be the same.
Tickle the choke/primer when trying to plane.
Is the motor a short or long shaft.Boat transom for short or long shaft. Short is about 15" long
about 20"Antivent plate just above the prop should be about even with the bottom of the boat.

 

[Jeffress77]

Re: Nissan NS40C mismatched prop???

When you say that the induction wire must not be near any other wire, what does this actually mean? There are not really any other wires anywhere "near" the spark plugs. When you say near, are you talking about touching them or 2 inches away or 6 inches away or 12 inches away? This tiny tach thing is so touchy and so many variables involved with accuracy, I cannot imagine how anyone would be able to see an accurate reading.

 

[steelespike]

Re: Nissan NS40C mismatched prop???

The plug wires they must not be near the other plug wires If its a 2 cylinder I would use the bottom plug wire.As a precaution run the wire outside the cover as soon as possible to avoid
any electrical contamination from the flywheel and charging circuits or the other plug wire.
If the plug wires are held together anywhere like a loop securing them against vibration. it could introduce stray pulses. I have seen some complaints about being finicky But to the best of my knowledge all have been successful.
Did a brief search on google what do you think of tinytach?
These were mostly on ATVs so rpm is up and down a lot and I would think hard to read bouncing around.
And vibration I would think could be a problem Basically no complaints about instalation,vibration or poor readings.
Only complaint was the slow update but these were 04-08 models new update is faster and a boat doesn't require as rapid an update.

 

[Jeffress77]

Re: Nissan NS40C mismatched prop???

Had great spark on both plug wires...engine ran fine.

Long shaft motor...antivent plate was just even, maybe ever so slightly above the bottom of the boat (exactness of the trim made the nly difference).


I took the Tiny Tach and tried it on my truck to see if it may be faulty, and it worked like a charm, first try, on my Dodge truck. So something is not right with the boat engine and Tiny Tach. I tried everything. I can get a reading "sometimes" but the numbers are way goofy and clearly 500-600 rpm higher than what they should be reading. We have the idle turned down low enough right now that motor barely stays running on its own..and if the Tiny Tach works 1/10 of the tries it will read 1200-1400 RPM. I have left an email and voice message with the company DTI who makes the tachs..hopefully I can get some answers.

 

[steelespike]

Re: Nissan NS40C mismatched prop???

Are you sure you have selected the right setting.As you said one pulse per revolution should work for a 2 stroke.I assume you set it for the 4 stroke setting on your truck.
We still haven't addressed your planing issue.Motor setup seems fine.
Even though you have a good spark you might want to prove both cylinders are actually working.
you could pull one plug wire at a time.Have you tried a little jolt from the choke/primer to see how it responds?Has the foam under the floor absorbed water.

 

[Jeffress77]

Re: Nissan NS40C mismatched prop???

Are you sure you have selected the right setting.As you said one pulse per revolution should work for a 2 stroke.I assume you set it for the 4 stroke setting on your truck.
We still haven't addressed your planing issue.Motor setup seems fine.
Even though you have a good spark you might want to prove both cylinders are actually working.
you could pull one plug wire at a time.Have you tried a little jolt from the choke/primer to see how it responds?Has the foam under the floor absorbed water.

Yes, I adjusted the Tach for the V8 engine at 4 sparks per revolution.
I pulled each of the wires off the the plugs individually and started the engine, and each one fired.
The boat isn't very heavy, as far as I know. There really isn't any water in it anywhere. It seems pretty dry to me.