NISSAN 5 hp 4 stroke lack of power

[RCARGAR]

I have a 2005 nissan nsf5bs that is low on power. It does not pop lean and i have thoroughly cleaned the carb and tested the pump...the float bowl is not running dry and if i remove the air cleaner baffle it is obvious that fuel pulls through the main circuit no problem...but if i choke it it will rev higher.The plug is not lean in appearence...or rich for that matter. I'm an automobile tech so carbs are not a mystery to me and this one is quite clean and idles fine. oil is not over filled. I tried a test that I use on cars which is to current ramp the coil...but i don't know if i should see the same result...a nice triangle with a staight falling edge on my scope. what i see is a hump that has no sharp edge. It acts like a week coil to me...choke it and the extra fuel gives the electrons something to flow on. Are coils a common problem?? Is there a better test I can perform...i'm not familiar with mag charged coils.
Thanks a bunch
Garland

 

[pvanv]

Re: NISSAN 5 hp 4 stroke lack of power

Coil issues are rare on these. We usually verify correct resistances with a good ohm meter, and if within specs, consider the coil to be OK. Of course a defective coil can test OK cold, and weaken when hot; YMMV. A weak coil usually results in a dark plug. Does the motor achieve proper WOT RPM?

Assuming that you are propped correctly (small motors are VERY sensitive to minor prop pitch changes, especially if pushing a heavy load), and that compression is good, you may have a slightly lean condition. That's typically inadequate fuel delivery, but can also occasionally be a vacuum leak.

I would check for any minor vacuum leaks at the intake manifold (elbow), and I would also recheck the float height (be sure the clip is on the needle). While you're at it, verify that the emulsion tube (nozzle) is spotlessly clean.

One thing that is often overlooked on the 4/5/6 is the valve lash. Makes a big difference in power. After 4 years of running, it's possible that the lash is a little loose. That can cause symptoms such as you describe.

The 4, 5, and 6 use different carbs, and that is about all that differs among them. If all else fails, you can run a carb for the 6. And yes, it does then deliver 6 hp.

 

[RCARGAR]

Re: NISSAN 5 hp 4 stroke lack of power

The motor does not achieve wide open rpm. The coil wire to either the spade terminal or white lead yields very high resistance...1.6m ohms . plug wire to coil core is about 14k ohms cold. using a fluke 88. The motor is original equipment on our Corsair 24 sailboat and i've owned it since new...original prop with no damage... the motor also exibits a tip in hesitation...then just boggs severely. This will happen right from start up with no change from cold to hot. The plug looks slightly rich..somewhat dark brown. I've pulled the carb down three times ...clean/compressed air etc. symtom remains exactly the same...not even a little improvement...i've been fooled by this symptom on automobiles using e-coils ...lean symptoms caused by a weak coil. i just dont know ballpark ohm specs...am I out of the ballpark??
Also the symtom is the same whether loaded in gear in the water or neutral on the trailer.I'm an auto mechanic 25 years and it sure feels like a lean problem and its a simple/clean motor and i can't find a fuel delivery issue or vacuum leak anywhere....figures I get offered a free boatlift for ten days and my motor is on the fritz...
Cheers and thanks for taking the time...
Garland

 

[pvanv]

Re: NISSAN 5 hp 4 stroke lack of power

Just off the top of my head (I'm not in the office today, so no service manuals at hand), those numbers sound like they're out of spec. Plug lead to core numbers are normally quite a bit lower than that. If that's the case (I can confirm that tomorrow), you may have a weak coil. You will also want to read ohms across the input of the coil (spade connector to white wire) for the primary resistance. Having the primary-to-secondary number (1.6M) is good to prove the coil isn't shorted, but you will also want a nice low ohm reading across the primary leads.

Please also verify (again) that the crankcase oil is not over full. I have seen quite a few 4/5/6 4-strokes that were overfilled, and low on power as a result.

FWIW, you can get a service manual at any Tohatsu/Nissan dealer, and it will have the coil spec impedance numbers in it. It will also have the valve lash specs, and compression specs. A worthy investment.

 

[pvanv]

Re: NISSAN 5 hp 4 stroke lack of power

Specs from the service manual indicate that you should get the following values (+/- 20% tolerance):
Exciter coil: Blk - Red/Wh 119 ohms
Pulser coil: Red -Wh/Blk 186 ohms
Alternator coil: Yel/Red - Red/Yel 0.39 Ohms

Also, for the ignition coil itself:
Ign coil Primary: Blk/Yel - core 0.02 to 0.38 ohms
Ign coil Secondary: Plug wire - core 3K to 4.4K ohms

 

[RCARGAR]

Re: NISSAN 5 hp 4 stroke lack of power

Incredible how sensitive this motor is to .....you guessed it....overfilled oil.I'm talking about FOUR OUNCES too much. Wow...what a difference. I changed the oil about 2 months before our last trip... and thats when I noticed the lack of power ..but I did not put 2+2 together until reading this FANTASTIC forum...thanks for your help. Hope this helps someone else.
Garland

 

[pvanv]

Re: NISSAN 5 hp 4 stroke lack of power

Glad you found it. Very common problem.

Oil capacity is a meager 15 ounces on these. That's less than a pint total, including that last ounce or so that never wants to drain out completely. That means you probably had almost 20 ounces in the crankcase, or about 25% too much oil.

Much like overfilling a car (if equipped with a horizontal-cylinder motor) by a quart or so. That will do it. Results in excess crankcase pressures, and a lot of material slinging around in that little crankcase. This will also result in "making oil", (see the FAQ's), which will only make things even worse.

We usually refill to half way on the dipstick. More is not always better ;-)