1999 NS18E2 Nissan 18hp motor has no power at full trottle when in gear

[JonBoatJim]

First time out this season. Ran great at full throttle to fishing area. Used trolling motor for several hours, then restarted motor. In neutral the motor idled and reved up fine. However when shifted to Forward, it would only rev to about 3000rpm at full throttle....5000rpm is normal. After running (sloooow going!!) a while, the motor would surge off and on a few times and finally it opened up to full speed at 5000rpms and got me back to the dock. I went out again and the same thing happened after shutting the motor off and switching to the trolling motor for a while. Motor idled fine in Neutral and in Forward.
What's happening? Is dirt getting to the high speed jet?

 

[pvanv]

Do you run only E0 fuel? Did you drain the carb for the off season? If not, clean the carb.

 

[Sea Rider]

Could be anything fuel related from tank to carb, clean tank, both fuel filters, carb, check fuel pump diaphragms condition, replace if found hardened, cracked, ballooned. Report your findings.

Happy Boating

 

[JonBoatJim]

I use "standard" regular gasoline and the motor was run dry at the end of last season. Will try carb clean first.

 

[pvanv]

Is your fuel ethanol-free (E0), or E-10 or E-15?

 

[Sea Rider]

Is it a low, medium, high hour use OB used in fresh or salt water ?

Happy Boating

 

[JonBoatJim]

Sea Rider and Paul, the regular gas in this area (Louisville, KY) is not E0. However, I'm not sure if is E-10 or E-15. The motor has been run in fresh water only. It has low hours. I've had it for about 5 years. The compression is balance at about 110-115 psi. I've serviced it every Spring after winterizing it in November.

 

[pvanv]

Start by cleaning the whole fuel system (including the tank strainer, the filter), and a Proper carb cleaning.

 

[JonBoatJim]

Paul, let me give you an update. I poured a can of Sea Foam and about 10oz of Techron into about 3 gallon of fuel. I ran it in a barrel at 3-4k rpms in neutral and then at 4-4.5k rpms in forward. I did this for hours, let it sit overnight and repeated the process the next day. I took it to the lake today....had the same low power, apprx 3K rpm (6MPH max) problem.... but maybe less duration before kicking into full throttle at 4500-5000rpms. The problem only seems to occur after the motor has set for a while maybe 5-30 minutes of so. Once it gets going at full throttle, I could would run it for 15-30mins at max speed (24 mph) without any problems. I ran it at full throttle/speed until about 1.5 gallon was used. Then after shutting down and sitting off for a few minutes, it had the same problem after restart.. I tried fooling around with the throttle and It seems that if I twist the throttle quickly, the motor will cough and sneeze and then it seems to take hold! Is this any help?

 

[Sea Rider]

It's a very bad idea running OB's at such high rpm when at idle and neutral for long time periods, if wanting running same do it while on muffs and geared forward at max 3 K rpm. Seems that carb needs a full internal ckean up soaked in dip carb cleaner while dissasembled ?

Happy Boating

 

[pvanv]

There is no such thing as a mechanic in a can. Seafoam has had marginal success for us. As a "maintainer", maybe, but certainly not as a "cleaner". Odds are the fuel system needs to be disassembled and cleaned completely. The other possibility is a thermal problem in the ignition, exacerbated by the hot soak. To test for that, try running with the cowl off for better airflow. The lack of throttle response is a clue that you may be running lean. Could be a bit of crud in the carb floating around, occasionally blocking a fuel passage.

 

[JonBoatJim]

Thanks for the advice Sea Rider and Paul. As I plan and order parts, should I replace all the fuel lines in the motor and the line from tank to motor? Also, I've tried to unscrew the motor's fuel filter bowl and I can't get it unscrewed! Should that be replaced?
Also, after when I launched the boat yesterday on first start-up (cold engine) the problem occurred immediately. ....so it doesn't appear to be a thermal problem.

 

[Sea Rider]

The OB fuel filter is a PITA to remove from housing. If using E fuels the bowl will be already expanded where it screws to the upper body making it extremely difficult to be removed. There are 2 options : Buy a new fuel filter assy or remove current one and flush it backwards with fresh water while connected to a water faucett for some minutes, once cleaned, mouth blow it dry, reassemble back.

For the fuel hose assy, once tank and inside mesh filter has been cleaned to perfection, add fresh fuel, connect connector to tank, get a proper container and place engine connector there, push white tip with something and hold it at open position, With bulb arrow pointing upwards, prime bulb several times till fuel exists on the other end. If fuel flows smooth throughout the hose assy with no restriction whatsoever, fuel hose assy is doing its homework right, no need to change it.

Disassemble carb and soak it in carb dip for some hours, afterwords spray a generic carb cleaner throughout the whole carb, assemble back, report if OB now runs properly.

One thing that maybe we're bypassing is : bad connector o'rings, could be hardened, worn, let air in and OB misssing badly, worse at middle to max wot range. Try testing with other fuel assy. If works OK, there's the culprit, replace both connector's o'rings, remove both with a thin needle, take to a auto store and buy exact same for fuel uses.

Happy Boating

 

[JonBoatJim]

Great explanation on the OB filter housing problem. Why back flush with water rather than gas? I could reverse the plumbing and use the tank and primer bulb to flush with gas.
I'll check out the O ring suggestion.

 

[Sea Rider]

Flushing with water while connected to a faucett achieves way more cleaning/flushing pressure than with primer bulb if wanting to remove the last bit of contaminants, particles poured into your tank when buying fresh fuel at service stations. You can shake and turn upside down the whole assy when flushing on a faucett than doing same while remains locked in OB holder..

When we used to have non E fuels, screwing off the cap was real easy, now mission impossible, worse if the cap has a dark yelolwish color. Many boaters here are skeptical that E fuels screws plastic, rubber way faster than non E fuels, so will need to live with it..

There's no such thing manufacturers are making such parts for E and Non E fuel uses, are exact same parts for both.

Happy Boating

 

[JonBoatJim]

Success!! I took the carb apart and thoroughly cleaned it. I used an OEM carb kit to replace gaskets, float, and float valve. I also replaced the spark plugs. The motor never ran smoother and I added another 1mph to the top speed!!

 

[JonBoatJim]

Success!! I took the carb off and thoroughly cleaned it. I used an OEM carb kit to replace gaskets, float and float valve. I also replaced the spark plugs. On the lake today, it never ran or idled smoother!! I also gained 1.2 mph in top speed!!

 

[pvanv]

Glad you got it !

 

[Sea Rider]

Now need to install an induction tach and check max wot revs achieved as loaded on flat calm waters to see if engine runs inside mim-max wot rpm range.

If current prop is a 9 pitch and combo happens to be mediun heavy will need a 8.5 or even a 8 pitch to have slight more hole shot with slight less top end speed.

Happy Boating

 

[Slamminsam9]

Newbee here...first post, so sorry if I mess up. But I'm having same problem with my Nissan 15hp...I believe its a 1992 NS15 BS . Starts up fine. Runs good until I give it power...it seems like its not going into "second gear". I feel like I'm getting 7hp instead of 15. It use to run, sputter and putter and go into "high gear" and away I'd go...running great. But just the other day, it didn't go through the sputtering into full power. It just wouldn't go to full power. So, I'm taking the carb off as we talk and soaking it. But I want to get a new carb kit...from other forums, I've heard they don't make or sell them. Defender says they have one...part number 300428...for a Nissan 15hp. Think this will work is my question? Any other suggestions....any help will be great.