2011 nsf9.8a3ef2 - out of box rough idling

[tal]

Hi there and Merry Christmas.

I recently ordered a nissan 9.8 4 stroke to use as a kicker on my CC Mako. Today I figured I'd start it up for the first time and see what happens. I put the oil in, fuel, etc and pulled the rope. It started on the third pull with full choke.

I let it run for about 2 minutes then eventually a little longer before I could turn the choke completely off and let it idle. While it's running at idle with no choke or throttle it seems to vibrate around a lot. If I speed up the idle or choke it smooths out with more rpms. I figured it would idle quite a bit smoother than what it is, is this normal?

I know it's only got like 4 minutes on it but will it smooth out? I really don't like the way it jumps and bounces around. Right it's worse than an old 2 stroke. I have some youtube videos I'll post when they're done uploading.

http://www.youtube.com/watch?v=uRe12cESTvo

http://www.youtube.com/watch?v=J0kh5hErJcM

I'm fiddling with the choke to keep the idle up. I'm thinking I might be worrying a bit too much and if anything the idle is a little low. The motor sounds good just a little rough and vibrating at idle.

 

[Sea Rider]

Re: 2011 nsf9.8a3ef2 - out of box rough idling

New engines out of the box sometimes have strange behaviours, go for factory recommended break in period at sea and check. Probably idle screw a bit rpm low ? Use fresh gasoline.

Happy Boating

 

[1fishbone]

Re: 2011 nsf9.8a3ef2 - out of box rough idling

I don't expect them to run perfect on the hose.
A little back pressure makes a world of difference.
Try it in the water.

I also agree with Sea Rider, get some time on it and see what it does.

 

[pvanv]

Re: 2011 nsf9.8a3ef2 - out of box rough idling

Merry Christmas...

Great videos. I think you will be OK. Couple of things of note...

These motors are set very very lean, required by EPA emissions rules, which leads to a whole bunch of characteristics that will be new and different from those of us used to 2-strokers.

In very cold weather, the intake manifold takes quite a while to warm up, especially with the upper cowl off. The temperature of the intake makes a huge difference in the atomization of the low-speed (near idle) air/fuel stream. A cold manifold makes it a really lean low-speed mix. In our western NY shop, in very cold conditions, new motors can take over 10-15 minutes to really warm up in the test tank, even though the telltale stream starts to get warm. You can use an IR thermometer gun (or the "hand on the manifold" test) to see when the intake is getting warm.

A little back pressure from being in the water (instead of on the hose) will help richen the low-speed mix some, and will give a smoother idle, so expect in-the-water idle to be smoother.

It's OK to have the idle stop screw at about 950-1,000 RPM (when fully warm) on these, especially if you will be doing some idling before fully warmed up. I would throw a good shop tach on it to see if you are too low. The videos sound like you may be down closer to 800 RPM.

The motor mounts on these are very soft, to reduce vibration transfer to the transom. As a result, any roughness at idle does tend to throw the motor around more than you might expect. But you will notice that on the flip side of that equation, the boat doesn't shake as much as you might expect when idled down low.

The manual choke linkage on these increases idle speed before adding choke, so a slight pull on the choke just increases idle. Since you were keeping it running by using only the first bit of the choke knob, you were increasing idle without adding choke. That makes me lean towards thinking that you have a normal carb setup, not a restriction in the idle circuit.

Of course, make 100% sure that you are not over on the crankcase oil. Not even a drop. Don't base your fill level on how much oil you put in -- Check it on the dipstick -- after the motor is sitting for a while -- so the oil has had a chance to drain off the internals and give a true reading. The crankcase only holds about a pint and a half, and the most common error is when someone dumps in a full quart. When new, we fill these to about 1/2 way on the dipstick, especially if they are going into service in cold weather, as all 4-stroke OB's will make some oil during break-in. We also use 10w-30 (not 10w-40) 4-stroke OB oil in colder weather. An overfilled crankcase causes rough idling, and will promote making oil, and can lead to pretty serious and expensive problems.

I think that after you get a few hours on it, verify the idle speed and oil level, it will smooth out just fine. BTW, we recommend running a water-separator on these, if at all possible (some boats aren't setup very well for mounting the filter), especially in colder weather.

 

[Sea Rider]

Re: 2011 nsf9.8a3ef2 - out of box rough idling

Some idling issues :

1-Tank cap vent closed position (open air vent)
2-Poor gasoline, use fresh higher octane gasoline.
3-Clogged fuel filter or carburator issue.
4-Mixture screw out of correct adjustment at idle
5-Idle screw at low rpm.

When engine is sufficient warm without ckoke put forward gear, if engine stalls out, idle speed at incorrect minimum recommended rpm. Once idle is ok, and still vibrating hard, check that friction bolt is properly adjusted, must feel some resistance when turning sideways. Anyway when enine is pushing boat swivel bracket will lock itself when cruising and engine will smooth out.

Happy Boating

 

[tal]

Re: 2011 nsf9.8a3ef2 - out of box rough idling

Thanks for all the helpful thoughts.

I think I'll follow the advice and put it in the water before messing with any settings. I did notice it was taking a long time to get warm and the 40* water from my rain water collection system probably wasn't helping. I probably have about 10 minutes idling time on it now so I need to get some pressure on the cylinders underway.

As for the oil, I have it about halfway up on the dipstick and I'm using 15w40 since I'll be operating in hot weather most of the time down here in Texas. I did notice the puff of blue smoke at initial start and I was thinking that may have been something from the factory or just residue oil ingestion from laying in the box. I did have it on the stand for about 24 hours before firing it up though.

I'm probably be using the panther heavy duty 4 stroke bracket that holds up to 263lbs since I'm limited to mounting space on my transom and a fixed mount doesn't help with varying water conditions. Here's a pic of my rig and where the thing will be eventually hanging. When I get the bracket on and go for the break-in I might take some more videos.