NS90A question

Snap43nib

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its a 92 or 93, I bought it last year and cannot get this thing to consistently run right, I had it running okay over the weekend doing some trolling (probably about 3 hrs on friday, 5 hrs sat morning, and 2 hours saturday evening, then sunday morning it just didn't want to run right, actually sounded like it was missing. Pulled the plugs and they were covered in oil.

Now since I bought it I deep cleaned the carbs, fuel tank, and changed the plugs. Anyone know what the compression should be on one of these? Or have any clue as to what the problem may be???

Thanks!!
 

pvanv

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Re: NS90A question

I would be surprised if you could idle/troll with a 90A for very long without plug fouling.
 

Snap43nib

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Re: NS90A question

so are are you saying there may not be anything wrong with this motor, maybe just some fine tuning? But trolling isn't an option????
 

TOHATSU GURU

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Re: NS90A question

No, that's not what he is saying. The 90 A will troll as well as any carbureted 2-stroke of it's same size. But, It's old...Would require the correct spark plugs...Would require the correct oil...Would require that the oil pump be set correctly...Would require the correct prop...Would require working electronics and would require a decarbonized block.

Chances are the your engine or any other engine of that era, would need to be brought up to the original operating standard in order to troll without fouling plugs too often.
 

Snap43nib

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Re: NS90A question

Okay that sounds a little better, well I guess I will go ahead a order a service manual, off hand anyone know what the fuel / oil ratio on these things are????
 

TOHATSU GURU

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Re: NS90A question

It's an oil injected engine so the rate varies depending on engine RPM.
 

Snap43nib

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Re: NS90A question

I did a compression test, its consistent but low (70), I cleaned the oil tank, lines, and pump. Whats the best way to bleed the oil lines?
 

Snap43nib

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Re: NS90A question

Whats the best way to tell if I should rebuild the carbs??
 

pvanv

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Re: NS90A question

Inspection of the carb internals will determine the level of cleaning required.
 

pvanv

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Re: NS90A question

I did a compression test, its consistent but low (70), I cleaned the oil tank, lines, and pump. Whats the best way to bleed the oil lines?
That information is in the service manual. Basically, you open a line and operate the pump to purge any air from that line.
 

Snap43nib

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Re: NS90A question

The carbs are clean and the compression is consistent, reed valves look good, I'm getting good spark, its starts right up. It runs strong except at lower rpms and its idles rough.

I'm thinking my next step is a carb rebuild kit, does that sound like I'm going in the right direction, or are there other tings to check 1st?

Also, fuel system was cleaned and filters are new. Any feedback or hints are greatly appreciated!!!
 

Snap43nib

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Re: NS90A question

I believe so, I have a manual on order and a carb kit coming, I guess when that comes in I'll check it out from head to toe. Exactly how is the timing adjusted in one of these???
 

sea_stork

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Re: NS90A question

"I did a compression test, its consistent but low (70), I cleaned the oil tank, lines, and pump. Whats the best way to bleed the oil lines? "


:eek:70lbs of compression? My NS70A2(70hp) has 150lbs on both, and my M40C(40hp) has 130 on both. Not bad for 20 year old motors.

70 is not worth working on, unless you want to rebuild it. The rings are worn out. It would be like a 50 hp 90.
 

Snap43nib

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Re: NS90A question

Im not relying on the #70, it was a borrowed gauge, I'm relying on the consistent #'s, I just can't get it to idle right or run at low rpms smoothly, when I had it in Lake Ontario last weekend it ran strongly except at low RPM's. But I have a nice honda picked out if this thing gets to expensive to get going.
 

pvanv

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Re: NS90A question

I believe so, I have a manual on order and a carb kit coming, I guess when that comes in I'll check it out from head to toe. Exactly how is the timing adjusted in one of these???

Correct timing will be achieved when links A and B and stoppers C, D and E are adjusted properly. Procedure is in the service manual. On a motor of this vintage and unknown service history, it wouldn't hurt to verify crank throw spacing -- to confirm that you don't have a twisted crank.
 

ChevyReb

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Re: NS90A question

I have a NS70A2 with the same symptoms...is the service manual or timing info available online? My carbs are clean and with new plugs it gets by but after a few hours it wont idle or go from idle to power unless you gun it quick. any hope?
 

pvanv

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Re: NS90A question

Chevy,

The service manuals are copyrighted, so are not posted online. Decarbonizing the motor may help. I would also do a compression check when hot.
 

ChevyReb

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Re: NS90A question

Thanks pvanv, but how do you de-carbonize the engine? Found this in search (http://forums.iboats.com/showthread.php?t=158076) A friend that has done some outboard work made a small adjustment to timing and it idles much better now, but it skips going from idle through mid throttle. Once you get it to 3/4 or full she levels out and runs great. I guess I'll buy the service manual...even though it states marginal print quality? I hope it is useable.

I did a compression check cold and had 126 on the bottom and 136 on top. I'll repeat that test after running it a while. Should I expect the numbers to go higher or lower with the hot engine?

Thanks again!
 

pvanv

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Re: NS90A question

That's a method that is often used to decarbon. Also, the Tohatsu "Engine Tuner" spray can fluid works well. Just make sure to allow enough "soak time" for the carbon junk to soften.

With any luck, once you complete the link-and-sync with proper timing, all will be OK.

Those compression numbers are OK. Might be a bit higher when warm, but just as likely not.
 
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