NS70A2 timing issue - Reference point error?

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!

The Factory manual is correct. At idle, anything around 4 atdc up to tdc will work.

Thanks - I kinda figured the chances of the manual being unclear or wrong were remote. It seems to run OK around TDC but the idle is definitely rougher and lower that what I would like, and the idle speed screw is maxed. I'm also not seeing much change by adjusting the pilots. I think the carbs are open too wide for the pilot circuit to do much. I spent a lot of time cleaning the carbs (pulled out the welch plugs, cleaned air jets and passages etc) and I am pretty confident they are OK.

Compression is lower in one hole. I am approx 115 in the lower, and 135 in the top, so I am at the lower spec (hot, throttle WOT). Think that would cause my idling issues? I've been through everything else. Carbs are spotless, did a good decarb, check valves are OK, fuel pump is fine, no intake leaks, reeds look good, spark seems fine, timing (as above), etc. The only other thing that comes to mind is a crank seal...

If I am reasonably confident it's a compression issue, I will probably throw two pistons at it and bore it 0.020. I got a copper head gasket for it, and a surprising amount of stuff from a NS90A crosses, and is still available.

You seem to have worked out timing issues with the NS70A2. That makes you a special person, because most folks won't even touch one of these old girls. I've got an issue I am tracking down on mine that is a '92 model. I suspect it could be timing or CDI heat-related failure if not some odd Carb problem I have overlooked. I just want to get this thing back to running perfect like it has for the last 5 years and then I'm selling her (and the spare NS70A2 parts motor I have at the house). Parts just too scarce. I would feel terrible selling this to someone and it not running right. She still has plenty of years left for someone willing to tinker every now and then.

So here it goes: Engine starts and idles up fine - as fine as a 30 year old 2 stroke can be expected too. Usually starts on on the first crank even after it had been sitting for a week on the water (something my 10 year Mercury couldn't do when it was new) - which has me believing the Carbs are not too far out of whack. Problem: Take off - go WOT and things are great for a short time (2 or 5 minutes) then the engine bogs down to no more than 2000 to 3000 rpms at WOT. Sometimes a restart will correct the problem for no more than another 2 to 15 minutes other times it does not.

It really feels like a fuel starvation problem I have experienced on other engines, however I've gone over all of the usual suspects and replaced most all of the fuel system. Definitely not a fuel pump issue. Carbs have been off, cleaned, nearly rebuilt, and no still change. Perhaps a float sticking or not rising issue? Maybe - but so far neither appear to be.


So, I am about to tackle the ignition. Hopefully at worse case I can get by with a new CDI. I just hate to spend $200 and find out it was an out of whack timing arm or got out of adjustment when I had the carbs off or doing some other work.

I don't even know if the timing would be a root cause. Unless it could slip or become unadjusted then magically get back to a proper position. I would suspect that if a timing issue was to blame it would not start or idle so easy anytime.

Have you any quick advice to help me make sure the timing is correct on the NS70A2?

Vettera said:

Have you any quick advice to help me make sure the timing is correct on the NS70A2?

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Mine ended up being low compression. It would pump up to minimum spec but would take longer than the other cyl, I opened it up and I had a bad cyl. I replaced it with a NS90A and am rebuilding the NS70A2 right now... All I would say is that I highly recommend buying a DVA adapter, I got along without one for years but finally bought one last summer, it makes troubleshooting ignition issues a breeze - especially with the factory manual.

I think the NS70A2 timing specs are OK, they are similar to what the NS90A requires and mine works fine at those settings.

When it dies, is the primer bulb full, or you get several pumps out of it before it's hard? It could be a fuel issue. That's probably easiest to diag first.