Nissan 90 syncronization

[Salmon Tub]

I am a new member here, so I would first like to say hello to everyone. I am a big fan of Nissan/Tohatsu, and have 5 of them myself. A 3.5, a 5, an 18, a 40 and a 90. The 90 hp Nissan is a late model 2-stroke that is on a 17' BW Montauk. In any case, I am having a difficult time adjusting my motor simply because I am not sure how it is supposed to run when adjusted correctly, I mean how smooth is smooth? The idle in water, out of gear is fine (900 rpm), the idle out of water on muffs is fine (1000-1100 rpm), but the problems start when in gear. I do a lot of trolling, and the previous motor that I had on this boat was a 40 hp Tohatsu, which also idled poor in gear (my opinion) but I trolled that boat at 1100 rpm in gear, so the trottle was always advanced a bit. The things that concern me with my 90 are the following: When out of gear but idleing in the water (back pressure), it is at 900 rpm, then the rpm's will drop to about 600 when placed in gear. The book (Clymer) and sticker on the engine call for 900 out of gear, 750 in gear. I can not seem to shrink that difference down from 300 to 150. It is the same with both a 15" and 17" pitch prop. I have set the timing per both book and sticker at 5 ATDC, original was set at 3 ATDC. I have checked all linkages, and the oil valve (not check valve), and they are all within spec. as per book. I have also adjusted pilot screws, and adjusted, and adjusted, and... to the point where I don't know if I will ever get her to run well. The page out of the Nissan shop manual (not Clymer) calls for 1.5 turns out +/- .25 turns and +1/8 turn for cold start. Pilot/mixture screws are not always a science, and that cut and dry. I have noticed that when in the water, in gear, if the pilots are way out of sync. but within spec., the needle on the RPM guage will start to jump from 300 to 600 rpm, there is little audible difference at that point in the sound of the engine. So, this I take as a tell tale when the pilots are seriously out of sync. The reason for all of these adjustments, is that outside of the obvious (needle jumping) the engine seems to vibrate a bit too much, more than my 18 hp Tohatsu at idle, which makes little sense to me. The vibration is not the shallow fast vibration, but a slow, un-even deep kick, that is just plain annoying. The most important problem is that Cyl. #3 fouls the plug fast (25 hours/20% trolling). Last year I had to come in on 2 cylinders due to a failed plug. That incident stays in the back of my mind every time I troll now, and I find myself a little hesitent to troll for longer than a half an hour. The last time I adjusted the pilot screws, (richened all up about 1/4 turn) I set them at about 2.125 open, 1.875 open, and 1.625 open, from top to bottom. This gave the highest RPM's was fine on the water, but when flushing at the end of the day, it would idle, then drop rpm's as if to die, then come slowly back up, then drop again. In order to stop this, I had to lean out the top, and richen up the bottom to 2, 1.875, 1.75, and this helped, but upon checking the plugs the next day, 1 and 2 were fine, but #3 was even darker than the previously. So, to prevent fouling, it seems I need have #3 leaner than 1.625 open, but that causes that roll when flushing as well as not running at top RPM's. One bit of reassurance was when I saw a Mercury 90 2-stroke running at the flushing station, it too seemed to have that kicking vibration, offcourse, it may be out of adjustment as well. I know this is a long post with a lot of information, but I would appreciate any help. How smooth is smooth on a 90 hp Nissan at idle?

 

[45_red]

Re: Nissan 90 syncronization

From your description of symptoms you might have your 90 idling better than mine ever has, I troll with a kicker. One thing you might try is some fine adjustment of the throttle plates to get the sync closer.

 

[Salmon Tub]

Re: Nissan 90 syncronization

Thanks for the reply, 45_Red. Offcourse, that is what I was afraid of. Once over 1600 rpm, it runs smooth, and quiet. I doubt I will ever get it to idle like a 4 stroke, and it seems to me that the older Yamahas and Evinrudes and even Mercs that I see idle a bit more smooth. Offcourse, these are 10 year old + engines that I look at, and I am sure they are not as tight due to age. I have looked at the throttle plates, but never ventured to adjust them, I have only measured their linkage. The plates look to be open equally to the naked eye, but that sometimes doesn't cut it. Any recomendations on how to get a more precise measurement? A feeler guage perhaps, but I have a hard time picturing how that would be done.

 

[45_red]

Re: Nissan 90 syncronization

What I have done with limited success; Open the butterfly on the richest running cylinder 0ne turn of the linkage rod& give it a good test.<br />One other possibility I suspect but haven't gotten around to checking is weak spark at idle speed.

 

[Salmon Tub]

Re: Nissan 90 syncronization

I adjusted the butterflies in all three carbs this last weekend. I used the method desctribed in the Clymer book. It is relatively straight forward. It seems that carbs #2 and #3 had been a little more open than #1. When I launched, and started up, the RPM's were lower than before, as can be expected. I brought them up with the throttle screw. It still showed signs of mis-adjustment by 1. bounceing Tach Needle, Grinding Sound, Shakeing. This too I had expected, since I had not touched the pilot screws after adjusting the butterflies. I tied the boat off to an end tie, put it in gear and started working on the mixture. By richening up #2 and #3, I was able to get the tach needle to stableize, and it seemed like the shake got a little smaller. The grinding noise was not present while tied to the dock. I took her out for a spin. Ran around at 3000-3500 rpm for about 15 minutes, then trolled for about 45 minutes. Grinding noise was present, needle was steady at 600-650 rpm, shakeing persisted, sometimes better, sometimes worse. Upon flushing, the engine again would run then pop (drop rpm's as if to die, then slowly recover) every 30 seconds or so. It was not as bad as before, but still prevelant. In order to prevent this, I had to richen up #2 and #3 yet again, almost to the point where all three are open the same amount. Then it ran fine on the flush, but this is with no back pressure on exhaust, and not in gear, as required by both Nissan and Clymer. Next morning, pulled the plugs to see that #1 was fine, #2 had fouled up compared to before, and #3 was even more fouled. Plug #3 was a new plug I had installed the previous day, so it had about 2 hours on it. By fouled, I mean, insulator is brown and electrode was now black rather than shiny chrome color. This would indicate that #3 and partially, #2 are too rich. In which case, if I lean them out, I will get the bouncing needle symptom back as well as the poping at washdown. I suspect the bouncing needle is due to a difference in power from each of the cylinders, due to unequal mixture settings. So, though the carbs are now truly synchronized in reference to the butterflies, I still have some work ahead of me. <br /><br />p.s. does anyone else get that grinding sound? It sounds almost like a horse voice. It comes and goes, and it definately exists only at idle, trolling speed, and it is actually effected by the water condidtions. On a flat pond, or when boat is tied off to a pier, it does not exist, when trolling in a swelly area, it comes and goes with each wave. In windy situations where there is wind chop, but no swell, it will come and go with the direction of the boat. I have 2 thoeries, <br />1. It is due to the effect of the water level in relation to the leg, meaning, as the boat enters the trough of a swell, and the transom sinks down a bit into the water, this increases the back-pressure in the exhaust just enough to cause this sound to appear. <br />2. It is due to the effect of momentum on the boat. At such a low RPM, there is minimal horsepower and torque created by the motor. It is relatively easy for things such as a headwind, climbing up a swell, or rough cofused water to create changes in the momentum of a slowly moving boat and so, effect the engine speed makeing the engine lug, then coast, then lug then coast. <br /><br />This would be fine, but the thing that concerns me is that there is no effect on the RPM's and they do not change or relate in any way to this noise. The noise could just be normal and inherent to the design of the outboard's exhaust system. So, has anyone else noticed this? I guess on a bigger hull, I would not notice these things, but my boat is relatively small, and that in itself, magnifies all of these things. It would probably run real rough, if I started it while it was just standing on it's skeg and not bolted to a transom!

 

[TRITONRULES]

Re: Nissan 90 syncronization

Hey Salmon tub<br /> This may be a stulid question, as I know nothing about engines, but is this 90hp nissan you are talking about a TLDI engine? The reason I am asking is that I have recently bought a Triton 1860, and am planning on hunting and fishing out of it. I troll during spoonbill season, and was looking at a 90 Nissan TLDI. I have narrowed it down to the Nissan TLDI 90hp, or the johnson 90hp. Trolling was makeing me lean more towards the nissan, but now I am wondering? Any help would be great? If youre 90 is a TLDI, how do you like it, did you figure out how to troll with it? Thanks Bill