Hi all, long time reader, first time poster. Beware, this may be long, but I will try my best to make it clear.
I have a NS70A2. It's never been great at idling but the last few years it's gotten worse. So, I have slowly been going through everything methodically and now am into the timing.
The factory service manual I have is not great. I have followed it to the letter (adjusted all rods etc), but the procedure for timing is described very briefly and the reference mark that is to be used on the engine isn't terribly clear to me. The manual says to use the parting line of the cylinder block and crank case as the reference to the timing set ring. I understand this to be where the two halves of the block meet - That vertical line.
The problem is that there's no way to actually time it using this mark, using the linkage rod lengths they identify (T - 13mm, A - 5mm, S - 94mm). The NS70A2 is supposed to be set at 4ATDC at idle and 22.5BTDC at full noise. If I use this mark, the engine is currently set to something like 27.5 degrees BTDC at full advance, and the high speed timing stop, even fully adjusted out, doesn't even come close to where it would need to be to stop things at 22.5 - The screw isn't long enough and even if it was, it would miss the flat spot on the arm entirely. Something odd is afoot. The other end of things, idle, is odd too. It can get to 4 ATDC in reference to the parting line, but it won't run there. Using the throttle control, the linkage first advances the timing, then opens the throttle plate. If I just pull up on the lever a tiny bit, to advance timing but not yet open the carbs, it starts to idle fine - Around where it's showing TDC in reference to the parting line. It's almost like I am getting too much retard at idle and it's killing the motor.
I thought it might be a sheared flywheel key. Nope. Pulled the flywheel, all is good. So I started thinking that maybe I was using the wrong reference point on the block - It would explain both issues.
So, in a fit of frustration, I went and found a copy of the newer Tohatsu 3 cyl and 4 cyl manual. The timing setup looks really similar, and it provides a bit more information. It states that "The seam at the mating surfaces of the crankcase halves is the alignment point for all ignition timing degree measurements." Seems clear to me. But then, in the procedure, it describes things as follows: "Align flat surface (4) of crankcase mold boss with calibration of set ring." Mold boss. Huh. And - No photo, diagram, nothing.
On my motor, there is indeed a boss sticking out of the block, with a casting web on it. And, if I measure the degrees from that point, lo and behold - I see 22.5 advance at full throttle, and it shows that it's currently set at 8 ATDC. So, armed with this knowledge, I adjusted the low speed stop to bring it to 4 ATDC, and it idles now - Not great, but better.
So, now I am confused. Are the manuals wrong as to what feature to use in reference to the timing set ring? Am I missing something?
My next move is to use a timing light. I made a timing pointer, used a dial indicator to find TDC, and marked the flywheel. I have to beg or borrow a timing light. That should clarify things a bit, but I thought perhaps someone here would have experience with these or other similar Tohatsu/Nissans. I really like this little outboard, even though it's a dinosaur with many NLA parts.
Thanks!
I have a NS70A2. It's never been great at idling but the last few years it's gotten worse. So, I have slowly been going through everything methodically and now am into the timing.
The factory service manual I have is not great. I have followed it to the letter (adjusted all rods etc), but the procedure for timing is described very briefly and the reference mark that is to be used on the engine isn't terribly clear to me. The manual says to use the parting line of the cylinder block and crank case as the reference to the timing set ring. I understand this to be where the two halves of the block meet - That vertical line.
The problem is that there's no way to actually time it using this mark, using the linkage rod lengths they identify (T - 13mm, A - 5mm, S - 94mm). The NS70A2 is supposed to be set at 4ATDC at idle and 22.5BTDC at full noise. If I use this mark, the engine is currently set to something like 27.5 degrees BTDC at full advance, and the high speed timing stop, even fully adjusted out, doesn't even come close to where it would need to be to stop things at 22.5 - The screw isn't long enough and even if it was, it would miss the flat spot on the arm entirely. Something odd is afoot. The other end of things, idle, is odd too. It can get to 4 ATDC in reference to the parting line, but it won't run there. Using the throttle control, the linkage first advances the timing, then opens the throttle plate. If I just pull up on the lever a tiny bit, to advance timing but not yet open the carbs, it starts to idle fine - Around where it's showing TDC in reference to the parting line. It's almost like I am getting too much retard at idle and it's killing the motor.
I thought it might be a sheared flywheel key. Nope. Pulled the flywheel, all is good. So I started thinking that maybe I was using the wrong reference point on the block - It would explain both issues.
So, in a fit of frustration, I went and found a copy of the newer Tohatsu 3 cyl and 4 cyl manual. The timing setup looks really similar, and it provides a bit more information. It states that "The seam at the mating surfaces of the crankcase halves is the alignment point for all ignition timing degree measurements." Seems clear to me. But then, in the procedure, it describes things as follows: "Align flat surface (4) of crankcase mold boss with calibration of set ring." Mold boss. Huh. And - No photo, diagram, nothing.
On my motor, there is indeed a boss sticking out of the block, with a casting web on it. And, if I measure the degrees from that point, lo and behold - I see 22.5 advance at full throttle, and it shows that it's currently set at 8 ATDC. So, armed with this knowledge, I adjusted the low speed stop to bring it to 4 ATDC, and it idles now - Not great, but better.
So, now I am confused. Are the manuals wrong as to what feature to use in reference to the timing set ring? Am I missing something?
My next move is to use a timing light. I made a timing pointer, used a dial indicator to find TDC, and marked the flywheel. I have to beg or borrow a timing light. That should clarify things a bit, but I thought perhaps someone here would have experience with these or other similar Tohatsu/Nissans. I really like this little outboard, even though it's a dinosaur with many NLA parts.
Thanks!