9.8 hp 2 Stroke Nissan Bogging Down

[8up]

Nissan Model NS9.8B, Serial Number 19303

Hello,
​ I'll try not to make this too long winded, but I want to give as much info as possible. I sold this motor a year ago in good running condition so I have a lot of faith in the motor (rebuilt the carb and used it for a whole season). The new owner contacted me recently about taking a look at because it's never been right for him, it bogs down when given throttle. I started and ran the motor on muffs for him when he bought it, ran great. He admittedly mixed the fuel/oil mixture too heavy on the oil initially, but remixed and tried again, same result. He has disassembled the carb a few times to try and solve this issue. He took it to a local reputable marine repair shop and they told him the motor had one cylinder that was not contributing, suspect reeds or ignition, 120 psi both cylinders( no charge, he said they didn't spend much time one it). He has replaced the spark plugs and the fuel filter. I have since done some digging myself to try and find the issue. I have done the following.
* Fresh gas with 3 oz TCW3 oil and 1 gallon fuel
* Pulled and inspected reed valves, no apparent damage. Cleaned, polished and reassembled with new gaskets.
*Checked exciter coil resistance: Blk & Grn wires 270 ohms
* Checked stop switch continuity open and closed, all good. Ran with stop switch disconnected
* Checked neutral safety switch continuity open and closed, all good
* Alternator Yellow & white wires resistance .3 ohms
* Pulled flywheel to inspect for any damaged magnets or coils, all good. Reinstalled flywheel
* At idle I can pull one spark plug wire at a time and the motor will continue to run, but you can definitely hear a slight difference. At higher rpm's removing one spark plug at a time don't seem to make as much difference the way the motor runs. there is spark at the plugs but I'm not sure how strong it is or needs to be? With the plug removed and the plug wire on and the plug grounded out, they both create a small blue spark. I have swapped wires and plugs and it doesn't seem to make a difference.
Any help would be great
Thanks,
Scott

 

[pvanv]

1. You are still running a little too much oil.
2. Compression is fine.
3. Since you have a siamese coil, if one fires, they both fire (unless you have a bad plug or wire).
4. That symptom is seldom reeds.
5. Stop and Neutral switches -- and alternator -- would not cause that.
6. I assume you are running NGK BP or BPR 7 HS plugs, gapped at 0.035 to 0.039 inch.

If the motor was ever allowed to sit with fuel in the carb for a week or more since the new owner got it, the carb likely needs a good cleaning.

 

[Sea Rider]

How old is that 9.8 OB ? Depending on age, how OB is kept when not in use could already have a faulty Ignition Coil unit, or faulty fuel connectors internal o'rings, usually dried, hardened, lets air in fuel flow and OB misses. Or a combination of both.

Happy Boating

 

[8up]

Thanks guys for the replies, the plugs are NGK BPR 7HS gapped to .038. I was told the motor is a 2002? The owner says the motor has bogged down on him since he bought it. I'm not sure how long it sat before he tried it. Another thing that I'm not thrilled about is that he removed the carburetor and took it to a Nissan OB shop and they checked it out said it looked very clean, but they went ahead and drilled out some ports for better air flow. I saw the 2 ports that were drilled out. I would say they are on the top linkage side the carb. Some sort of jets, I don't know? Maybe ya'll know what they are for. I tried to block them with my fingers while running and it didn't make a difference.




I would describe the sound of the motor as running kind of "flat" as you increase the throttle.

"Since you have a siamese coil, if one fires, they both fire (unless you have a bad plug or wire)." Can you explain this a little for me please? Does it matter which wire is on what cylinder? I would sure think so? It seems to run the same either way.

Thanks again, look forward to hearing some more input

 

[pvanv]

Both plugs fire in unison. One is doing a "wasted" spark in exhaust. Typical of 2-stroke 2-cylinder outboards. I would not like some hack drilling the air passages of that carb, as it is 100% guaranteed to make the carb worse.. You may very well need a new carb... and may have needed it -- or a very good cleaning -- for years. Previous owner was a dolt, and the shop he went to was worse. Check prop pitch, see if you can get a lower pitch to ease the load on the motor if the current pitch is high. If you do end up needing a carb, they are about $191 new from any Tohatsu dealer. But try a Proper cleaning -- in real carb dip -- first.

 

[8up]

Thanks for the explanation on the spark, make total sense. I checked out the spark using my spark tester (adjustable kind you connect the plug wire to and clip to ground). I set the gap to 7/16" and it jump the gap on both wires with no issues at idle. I should say that when I first bought this motor a couple of years ago, my buddy rebuilt the carb for me. it was disassembled and cleaned in an ultrasonic cleaner. Like I said previously, I used it for that whole season and it ran strong and was running strong when I sold it. I spoke to the current owner last night and he said it was bogging down before he took the carb to the Nissan shop that drilled out those passages. I'm assuming like you guys have said, it sounds like a fuel issue at this point, I think I've checked everything else? I suppose it's possible that it sucked up a piece of trash in the carb after he got it home and has never been right? Now that that shop drilled out those passages, they kind of screwed it up, it doesn't look like those ports were threaded, if so...they drilled out the threads. I told the owner that I have done everything I could do and that I recommend he take it to a local shop to make sure that is the issue. Thanks for all the help on this, let me know if ya'll have any final thoughts.

 

[8up]

Another update, I have been continuing to work on this outboard trying to figure out what the problem is. I removed the carb, disassembled and cleaned in my buddies ultrasonic cleaner for about 30 minutes,checked all the small holes in the jets etc... I reassembled it and installed it and it ran about the same. I installed the spark tester and tested at higher rpm's and recorded it in slow motion on my phone. I am actually able to see the misfire in the ignition system. I wish there was a way to upload the video to show you, but that is a whole other challenge. Anyway I have recorded misfires on both plug wires and from what you guys have said, that is consistent with a siamese coil right? These misfires appear to be totally random. As a reminder I have removed the flywheel and checked for damaged or loose magnets etc.. After all this troubleshooting, is it safe to assume that this motor needs a new CD unit? Link to the video, but its not in slow motion. You can get a much better feel for the timing and rhythm in slo motion. You can still see the mis.

http://vidmg.photobucket.com/albums/...123A6F779E.mp4

 

[Sea Rider]

Being a one piece CD/Ignition Coil unit any one could be already shot, will need to replace complete unit....

Happy Boating

 

[pvanv]

You could run ohm tests on the CD as per the Factory service manual.

 

[8up]

I don't have a factory service manual for this motor. Would someone mind helping me out with the procedure, wire color and resistance? Any help would be great.

Thanks again,
Scott

 

[Sea Rider]

Scott,

Electrical components have 3 conditions :

-Works spot on
-Misses, works erratically
-Are shot, kaput

Second cond is the most dificult one to troubleshoot/diagnose properly, although you can measure them with a appropriate instrument when cold, could altered themselves once OB is running, shorts, heats up and component misses. This unit is not bullet proof, although lasts long, could fail the sooner or latter. What's the cost of a CD/IC unit ?

Was the electrical test done while OB was on muffs, barrell ? If so, surely will miss much worse under load while combo is running on water..

Happy Boating

 

[8up]

Thanks for the reply, the cost varies from aftermarket @$100 to OEM @$250 roughly. I just want to make sure I have done everything I can with what I've got before saying "you need one of these". The test were done on muffs. The owner brought me a Seloc manual but it doesn't touch on this exact CD unit from what I can tell.

 

[Sea Rider]

That's why I stock needed 3 electrical components as spares at hand, no wasting precious boating time troubleshooting them, just swap and voil?, usually the Ignitiom Coil is the culprit on the 18 teens. Only info could find on Tohatsu Service Manual for 9.8 OB's is :

-Exciter Coil (disconnect CD) 224-336 Ohms.
-While cranking 100 DVA minimum. Need a tester that reads DVA Volts.
-Secondary Coil Resistance : 1.95-3.25 Kilo Ohms
-Output while cranking : 198-220 DVA, same tester.

But as said before if CD/IC unit alters while working those numbers will be just a "cold" refference.

Happy Boating