Nissan 9.8 will not idle

[Snapdragon]

After running my Nissan NSF 9.8 A2 EF4 four stroke for several hours it shut down unexpectedly just as I reduced throttle. The electric starter would not work, but the engine would start manually but only run at a high throttle setting. Several attempts to reduce engine speed in order to engage forward gear resulted in the engine stalling before a reasonably low rpm could be established.
So far, my troubleshooting has revealed that the 20 amp starting circuit fuse is blown and both the red wire and white wire to the rectifier/regulator is showing zero ohms of resistance to ground even when disconnected from the rest of the electrical system. I suspect that the rec/reg is faulty and caused the fuse to blow, which disabled the starter solenoid circuit.
The engine seems to run raggedly when started, and seems to only be running on one cylinder. I have not been able to determine if there is a carburetor problem yet, but I have changed to a six horsepower Tohatsu four stroke to prove that the fuel system is in good shape up to the point where it enters the engine.
All this to ask the question; Has the rectifier/regulator indeed failed, and if so would it cause the engine to stall at low speed?

 

[pvanv]

Re: Nissan 9.8 will not idle

You may have two separate problems.

Yes, if the red charge wire from the rectifier/regulator is shorted to ground, that could blow the fuse. Once the fuse is blown, the start signal can't get to the starter solenoid. That will prevent the electric starter from working, but will not affect running at all, as the alternator/rectifier/regulator is completely independent from the pulser/exciter/cd ignition system. The rectifier may or may not be bad. You need a good analog (not digital) ohm meter to test the electrical system on these motors. Because the rectifier is a "bridge", with 4 diodes in it, the checks need to be taken in "both directions", i.e. the red wire should read "open" in one direction, and if you reverse the tester leads, it will read "short" (about 9K ohms) in the other. There is a "matrix" of tests for the rectifier, which is too complex to list in a post on this board. Full testing info is in the Factory service manual, Part # 003N210561, $40.00, available from any dealer, including me.

As for the running/idle problem, you may have an overfilled crankcase (typically will cause those symptoms), or a fuel system issue, such as a varnished-up carb (common), or an ignition issue (rare). I would check the oil level. If overfilled, check for fuel in the oil. If no gas is in the oil, yet it's overfilled (even a drop high), lower the level to about 1/2 to 3/4 on the dipstick. If you smell a lot of gas in the oil, pull the fuel pump and check that it isn't leaking fuel through to the crankcase. You can do that by connecting the primer hose and squeezing the bulb. If there's a diaphragm leak, it will be immediately evident.

If suspecting the rectifier/regulator, you can unplug the rectifier's red wire, isolating it from the rest of the system, change the fuse, and the rest of the systems (aside from charging and tachometer) should work properly. Beware; If the crankcase is very over full, operating the electric starter could possible shear the magneto key.

 

[Snapdragon]

Re: Nissan 9.8 will not idle

OK, it looks like three problems, not just two.
First, I unplugged the red wire to the rectifier/regulator and put a new 20 amp fuse in the starter circuit. The starter now works perfectly.
Next, I checked the oil level, and indeed it was a bit high and had a definate gasoline smell to it. When I drained the oil, it seemed to have the viscosity of water and was obviously diluted with gasoline. I checked the fuel pump for leaks, and found a slow drip inside the valve cover, and thus into the crankcase, when the fuel line bulb was squeezed.
After installing a new rebuild kit in the fuel pump I filled the engine to the proper level with oil and started the engine. It still would not idle, but a check of the spark at the plugs proved that both cylinders were fireing.
I then removed the carbureator, disassembled it, blew compressed air through the jets, and carefully reassembled it.
This time, when I started the engine it was as if it were brand new! It now idles perfectly. Thank you so much for your kind help and advice.

 

[pvanv]

Re: Nissan 9.8 will not idle

Cool beans.

Remember that any 4-stroke OB will tend to make oil, so keep the level a little below the full mark.

Also, be 100% sure to religiously disconnect the fuel line at the end of each and every day (unless you know that you will definitely be using the motor the next day), and allow the engine to run until it consumes all the fuel in the carb and stalls. This will have 2 benefits: 1- you won't have fuel sitting in the carb to varnish, and 2- any expansion of the fuel (due to sunlight heating) won't rupture the fuel pump diaphragm or flood the carb.

Now all you need to do is test the rectifier. If it checks OK, you can reconnect it. If it's bad, it only takes a few minutes to install a new one. Be aware that if you are running without a battery, you cannot allow the battery cables to short together, or you will likely blow that fuse again, and may cause other issues as well.

 

[Snapdragon]

Re: Nissan 9.8 will not idle

Thanks for the tips Paul!
I assume that the same rules apply to the new Tohatsu 6 hp four stroke that I'm using as an alternate to the Nissan 9.8. I plan on using these motors in several different applications and it will not always be convenient to use a battery with them.
I'm pretty sure that the rectifier is totaly fried on the Nissan, but I'll just wait a while before investing in a new one. The solar panels seem to be doing a good job of keeping the battery bank charged.

 

[pvanv]

Re: Nissan 9.8 will not idle

Yes, all 4-stroke OB's behave similarly. They work best when run hard and hot, and may make oil when idled a lot, or run in very cold water. Likewise, the best motor oil to run will be non-synthetic NMMA FC-W rated 10w-30, unless it's above 90F, in which case, you can go with 10w-40.

For electric-start motors that are frequently taken on and off the boat, I like the Minn Kota MKR-20 Trolling Motor Plug. Handles up to 50 amps, and is a solid connection, yet allows for a quick disconnect, without exposing the wires -- so they won't short together -- so you don't blow the rectifier. The same kind of plug is sold by Warn for use with electric vehicle winches. Prices run about $20-$40, depending on brand.

You can also equip the MFS6 for charging. The exact kit needed will depend on the specific model of the motor. Some require a different flywheel, others just need the alternator and regulator/rectifier.

The part your 9.8 will need to get the charging system repaired is 3AA760650M, RECTIFIER, $93.98 msrp, available from any dealer, including me. I would also test the alternator coil, to confirm that it didn't get fried when the rectifier burned out.

 

[Snapdragon]

Re: Nissan 9.8 will not idle

Actually the little motor is a MSF6CS Sail-pro with factory installed charging kit, which explains my interest in protecting the charging system while running with no battery connected. I can use either of these motors to push my 26 ft Snapdragon bilge keel sailboat, or the dingy, or a 14 ft aluminum fishing boat that I sometimes play with.
The 6 hp Tohatsu will move the sailboat almost as well as the 9.8 Nissan will, but only uses about half the fuel. It's good to know that the four stroke engines can tolerate pushing a heavy load ( 5,500 lbs ) without risk of heat related problems! Cold water is usually not an issue here in the deep south.
I'll be seriously looking at those Minn Kota MKR-20 plugs for my cockpit charging connections for the motors and for the solar panels and tiller pilot as well. Good, dependable, interchangeable electrical connectors are a good investment when the weather kicks up.
Thanks for the part number. I'll let you know when I'm ready for it.

 

[pvanv]

Re: Nissan 9.8 will not idle

While the 6 sail pro will push your sailboat OK in calms, you will definitely prefer the 9.8 in a chop. I push my 8,000-pound Hinterhoeller HR28 sloop with a Nissan NSF9.8A3. (See my avatar). In theory, it calls for at least a 15, but the 9.8 cowl fits into the lazarette much better. In my case, I run the 4-blade 5-pitch HT prop, which gives stellar control, especially in reverse.

The MKR-20 connector will be a little big and cloddy for the tillerpilot, but should be OK for the other connections. The solder connections are not designed for smaller wires, such as 16-gauge, but I have used them very well with those smaller wires, such as my peltier-effect refrigeration (coleman 12v cooler). I needed a better connector because the cigar-lighter plugs aren't up to the task, and tend to overheat. To do the solder, I strip about double the normal length, and then double-back the bare wire before inserting it in the contact.

Unfortunately, the only current "standard" connector for 12vdc is the cigar lighter type. It's OK for about 1 amp, but at 4 amps continuous (such as for my cooler), even the best of those connectors tend to overheat and melt (especially on hot days), because the contacts between the socket and plug aren't really solid.