8/9.8 hp Nissan peters out on low revs

[Plandeck]

...I dunno...did this carb upgrade thing many years ago with a small British sports car and never found it made a difference...I may go back to the triple blade prop next year to see if it brings the revs up and sacrifice the enhanced reverse control at low speed...I guess I needed the reverse choke setup anyway for the automatic choke so I'm not sorry about the switch...but I'm still not satisfied with the tach installation...I now have the 2 wires to the instrument light hooked up to the running lights...and the hot wire for the oil lamp directly to the electrical panel...this allows the tach to run when the sailboat's electric switch is turned on even when running lights are off...but I still get the oil lamp on all the time...I thought if I ran the tach oil lamp hot wire to the oil switch hot wire that would work but no dice...I got no tach or oil lamp light...so I'm confused why the tach won't run without the oil lamp lit red all the time. I have another LED lamp on the oil switch which never lights. Should the oil lamp light initially when the ignition is engaged (the cut off switch lanyard in place) and then go out when the motor starts to run? I remember it used to work this way...AND THE OIL LEAK IS MUCH IMPROVED NOW WITH OIL DIP STICK READING HALF EMPTY..

 

[pvanv]

The 8 hp version is a de-tuned 9.8. Period. The bigger carb definitely gives you 22.5% more power -- but to get and use that power, you must have the proper WOT RPM. If you are lugging, you are not getting that power. You need less effective pitch. Period. Depending on the tach reading (you said that you are only about 4800 max, and you want 6000 for sure), switch to the 5-pitch HT prop. Yes, going to a 3-blade prop will increase RPM, but so would running a 2-blade prop, or for that matter running with no prop at all. The object is to transfer thrust to the water, pushing the boat. The more blade surface, the more that transfers to the water. Old displacement sailboats are like barges... Slow speeds (not planing), and they need good throttle response/control. That is why the HT prop was designed and made. There is a slight possibility that running with a much higher slip proportion (the 3-blade prop) that you would go a little faster, primarily because you would have higher RPM, but when do you actually want that characteristic? Remember that it is an aux. sail vessel. You are supposed to be sailing. The motor is to get on and off the dock, or to help get home on a stormy or windless day.

You are still wired incorrectly.
Instrument lights are supposed to come one with the running lights (just like any other car or boat), so you have that part right.
The tach is always supposed to run when the motor is running, so it seems you probably have that part at least partly right. None of the tach wires are supposed to go to the wiring panel except power and of course instrument lighting. The Oil light is not supposed to go to the boat's hot on the wiring panel. That is why it's on all the time.

The oil light is supposed to come on when you are below about 4 psi oil pressure, and the motor is switched on, whether running or not, and whether the stop clip is engaged or not... just like the oil pressure LED. Refer to page 24 of the owners manual. Follow the wiring diagram; don't try to re-engineer the wiring. Use all the wires that are in the diagram, as designed, and it will work correctly -- just like mine does on my 8,000 pound sailboat. Period.

It is a simple thing to track down an oil leak. There are only a few gaskets, and I believe you have already replaced all but perhaps the head gasket. Is the dipstick stopper damaged? Do you have a cracked block?

 

[Plandeck]

...am following the wiring diagram (that came with the tach) as much as possible since my harness is for a tiller model and the tach diagram is for a remote control one. 6 wires. 2 for instrument light to running lights. 2 for tach to alternator leads yellow and white. 2 for oil lamp...1 to lamp ground and 1 to ?...here is problem...on remote control model it goes to red...but I have no red...I have red/white which is hot wire for oil pressure switch...but this is in off position unless there is drop in oil pressure...so where to connect oil lamp hot lead other than boat electric system hot wire...then the tach runs but the oil lamp is on constantly. If oil lamp hot lead goes to oil switch hot wire I get no lamp and no tach...is your harness a tiller model? not sure the tach will wire properly to a tiller model harness....

 

[pvanv]

...am following the wiring diagram (that came with the tach) as much as possible since my harness is for a tiller model and the tach diagram is for a remote control one. 6 wires. 2 for instrument light to running lights. 2 for tach to alternator leads yellow and white. 2 for oil lamp...1 to lamp ground and 1 to ?...here is problem...on remote control model it goes to red...but I have no red...I have red/white which is hot wire for oil pressure switch...but this is in off position unless there is drop in oil pressure...so where to connect oil lamp hot lead other than boat electric system hot wire...then the tach runs but the oil lamp is on constantly. If oil lamp hot lead goes to oil switch hot wire I get no lamp and no tach...is your harness a tiller model? not sure the tach will wire properly to a tiller model harness....

You aren't following the diagram in the Factory service manual; Since you are using a retrofit remote setup, you must look at how your particular system is wired. What are you using for an RC box and key switch? The oil light does not get wired to continuous 12v (Motor red), even on P models. The wiring harness is identical on the motor side for all models.

The oil light is supposed to light when the oil pressure switch triggers. The Light Green grounds when the oil sender switches to ground for low pressure. That completes the circuit for the oil lamp. The Red coming from the RC box of P models switches ON when the key is ON (switched 12v). So, the tach assembly powers up when the key is switched ON, and the oil lamp grounds when oil pressure is low, triggering the oil lamp. You need to locate your switched 12v, and connect the tach assembly power wire to that.

If you follow the wiring diagram in the back of the Factory service manual (available from any dealer, including me), all will be clear.

 

[pvanv]

No Title

Here is the pertinent half of the diagram from page 10-6 of the Factory service manual:

 

[Plandeck]

all will be clear...very funny...from what I can make out on the manual diagram the red wire is always hot when the key is turned on. If red is hot the oil lamp will light because the ground on the oil switch (LG) is always active. The way I remember it working is the oil lamp lighting when the key is turned on, but when the motor starts the oil lamp stops lighting. Don't know how they do this. Bottom line is unless red is hot the tach will not run and since the oil lamp ground wire (LG) is always grounded the oil lamp will not turn off. To set up the remote on my boat I simply extended the lanyard setup to the remote location. The key is 3 position, first turning on the blower then activating the starter. The motor starts with or without the key engaged. OOKKOK

 

[pvanv]

Peter,

Yes, power to the tach must be supplied any time the key is ON. No, the Lg is not always grounded.

The oil sender grounds the Lg wire only when oil pressure is low. All oil pressure lamps of all types have worked this way since the 1950's. (That's "how they do this", and they have done it that way for over half a century, even on Chevrolets).

The key should supply power to the tach when in the ON (RUN) position (this is called switched 12v). If the blower always runs when in the ON (RUN) position, that is also the location for the red tach wire. The only real electrical difference is that the Factory key switch also grounds the stop (Br) wire when turned OFF, whereas your aftermaket system may require you to push a separate STOP button, unless it has that STOP wire feature... if it has that feature (and it is wired to the Br wire), pull starting will not cause the motor to start when the key is OFF.

HTH (hope this helps).

 

[Plandeck]

...I follow and there must be a problem with the oil switch otherwise the LG wire connected to the tach oil light would not continue to ground after the motor runs...as you say higher oil pressure should disable the switch...but the oil lamp remains on with the motor running...funny thing is the dedicated oil lamp running to LG and W/R as shown on the diagram does not light...ever...even when the key is turned but the motor off...W/R is where I hoped to get a constant hot lead for the tach off the motor battery instead of the boat aux 2nd battery....but it's never hot...but I'll double check all this again now that it IS CLEARER....

 

[pvanv]

Pressures above about 4 psi cause the sender to open the ground. You could check that with any decent ohm meter or continuity tester. Disconnect the wire from the sender and test across it for continuity. t should be low resistance. Start the motor; the sender lead should show high resistance to ground.

Are you connecting the tach light to the Lg that is attached to the oil pressure LED? That is the wrong location. The Lg that originates at the CD module (that normally connects to the RC box) is the proper signal ground connection.

The onboard LED is very low power, and if you attempted to supply switched 12v to the tach oil light from the W/R that supplies it, you may have irreparably damaged the driver in the CD box.

 

[Plandeck]

No Title

...absolutely positive Lg from the boat harness is active ground either when motor is running or not (see attached photo)...I don't find a 2nd Lg from the tiller harness...nor is there one shown on the wiring diagram that covered the connections box...

 

[pvanv]

If you review the wiring diagram in the Factory service manual, you will find there are two Lg wires on the EF models. One connects from the warning lamp to ground (originally at the coil), the other runs from the CD to the Br/W that goes to the oil pressure sender switch. Of course the Lg that connects the LED warning lamp to ground is always grounded. The one that connects the sender to the CD clicks to ground below about 4 psi, and opens above that. That is "how they do that".

 

[pvanv]

Look in your Factory service manual; find the diagram for the EF model in the back; There are two Lg wires; One connects the LED to ground. That will always be ground. The other originates at the CD, and connects to the Br/W of the pressure switch. That wire goes to ground below about 4 psi. That is the trigger for the low oil pressure lamp. That good old Factory service manual comes in very handy...

 

[Plandeck]

...regardless, if the tach oil lamp wire is un-grounded the tach itself will not run...I'm pretty sure...

 

[pvanv]

...regardless, if the tach oil lamp wire is un-grounded the tach itself will not run...I'm pretty sure...

Incorrect. Oil lamp ground is only for the oil lamp. INSTRUMENT ground is the yellow wire. Grab that Factory service manual, review the beautiful color diagrams, and it will start to make sense.