nissan 9.9 2 stroke: Problem while in forward gear

The engine was made somewhere between 1988-1992. I got the motor in late fall and it had a rough idle so i gave the carb a good cleaning, adjusted the air to gas ratio screw and idle screw. The engine ran great after i did this until recently.

I launched the boat, got it started and everything seemed fine. I drove out to my first fishing spot and when i tried to leave there the engine wouldnt start. Finally after about 50 pulls it started and ran for about 10 seconds then died again. Another 20 pulls went by then it started again only this time i had to keep it at full throttle to keep it from dying. My tach was only reading 1500 rpms, which is obviously too low for full throttle, any throttle lower than this the engine would die. After staying full throttle for about 30 seconds the rpms started to rise, so after about a minute of slow acceleration i was finally at WOT (around 5500 rpms). Everything seemed normal about the engine at anything above 3000 rpms, when i got too slow the engine would bog down and make me restart that super slow acceleration. If the rpms stayed high enough i could change speeds like normal but not at slow speeds. i tried turning the engine off and tying it over again but it was the same thing every time.

i went out again today and it did the same thing as last time. I have no clue what this could be.

Also the engine does not have this problem in NEUTRAL, only in FORWARD or REVERSE. In neutral everything seemed to be just fine, idled and revved up to 3000 rpms (half throttle).

Please help me figure out whats wrong so i can have it fixed. Thanks in advanced

Most motors sound good in nuetral because they do not have to do any work !----------So check compression , check to see that you have spark on both cylinders.----Check fuel pump diaphragm.-----This could be as simple as a bad sparkplug.

I put in new spark plugs about a month ago. i would hope they are still good. I have not yet checked the compression but both cylinders should be working because i can still get up to full speed still. What would I look for in the fuel pump?

Probably just water in the fuel then.

Can you explain how that would only cause the engine to work correctly in nuetral and not in forward and reverse? From my understanding, if there was water in the fuel it would mess up the engine in neutral as well as forward and reverse.

thanks for the quick responses

Almost all OB's that have fuel issues run better in neutral, since there isn't any load on the motor. You could have something as simple as water contamination, or some varnishing of the low-speed circuits in the carb. The only way to be sure is to diagnose -- rather than guess. Use your trusty Factory service manual as a guide. Verify 50:1 oil mix in the fuel, verify fresh (under 30 days) fuel, and no water. Check plug condition. Check compression. Inspect the plug wires, and test the CD. Disassemble, clean, and inspect the carb. Be aware that there are precious few (if any) parts available for that obsolete carb, so proceed with care and caution, knowing that if the carb or a critical part of it becomes damaged, you have a doorstop instead of am outboard.

The motor only " sounds good to you " in nuetral , it does not have to do any work so it will rev up.-------Means nothing as far as good trouble shooting goes !

okay so i took the boat out again with a brand new oil and gas mix in the tank. Only this time the engine would barely run at all. Also i discovered that the carb was leaking around some of the seals.
Looks like I need to take it in to get some service. Or does anyone know where i can buy the seals and do it myself?

We need your exact model/serial (year is unimportant for servicing a Nissan/Tohatsu). Odds are that if you have a 9.9B2, you are probably out of luck. If you have a 9.9C, the carb kit is still available, from any dealer, including me. The seals/gaskets are probably not "leaking". The float is probably overflowing.

The float overflowing makes perfect sense. What would be done to fix that? i will try to make my way to my boat shed later to look at the serial number. All I know right now is that it starts with a 4

Checking/cleaning/adjusting the carb is called for. But again, if you have too old a model, you may end up scrounging for carb bits at a NAPA -- possibly ending up with something like a motorcycle carb needle or something like that, or in a boneyard. You can get a Factory service manual that covers the procedure, or take the motor to a dealer for the work.

pvanv said:

Checking/cleaning/adjusting the carb is called for. But again, if you have too old a model, you may end up scrounging for carb bits at a NAPA -- possibly ending up with something like a motorcycle carb needle or something like that, or in a boneyard. You can get a Factory service manual that covers the procedure, or take the motor to a dealer for the work.

Click to expand...

Thanks for the tip. Cleaning the carb did the trick. It didnt appear to be dirty inside the carb but taking it apart and spraying it with carb cleaner made the engine run great. i checked the compression too. It was good at 145 and 140 psi

The serial number is 47088. Can you please help me figure out which model my engine is and if ill have access to parts in the future?




Also the engines fuel filter is full of gunk and have tried to take it apart and clean it but with no luck. would i have to replace it or is there a way to clean it?

The serial plate should have the model. Should be something like NS9.9C or similar. Just buy a new filter from any dealer, including me. Oh, and at the end of each and every day, be sure to disconnect the fuel line and let the motor run out of gas. That will help reduce the fuel varnishing.

Looks like a 9.9B2. If so, there are 2 different possible carbs -- one with an octagon-shaped bowl (newer units), and one with a round bowl (up to serial 22451). Internal parts for the carbs don't interchange. The fuel filter is 346022300M, FUEL FILTER ASSY, $13.63, available from any dealer, including me.

Thanks for the help. Theres one problem with finding the model, one of the previous owners took it off the engine. You can see in the first picture i posted where it used to be. Also i do try to run the gas out every time and i use a fuel stabilizer too. How would i order the fuel filter from you?

You can drop me an email at the office: [email protected] or call 716-877-8221 9-5 M-F Eastern and we can help you.