Nissan NS70A2 problems

[telfish]

Hi <br /><br />I have a Nissan NS70A2 its a 70 HP 2 cylinder 2 carb model that is giving me major problems. <br /><br />If I take my boat out it will start and run all day at up to three quarters throttle. If I run it wide open the revs will die after a short time. Then I have to limp back to the dock at low revs and 4 MPH. I can then no longer get it to run properly unless I let it rest for a day. I have changed the spark plugs and added various treatments to the fuel to clean the carbs and take any water out of the lines.<br /><br />I'm pretty sure that I am running on one cylinder when the revs suddenly drop off. Any ideas, and I am damaging the engine by limping back to the dock on one cylinder.<br /><br />Thanks<br /><br />Tel

 

[JB]

Re: Nissan NS70A2 problems

Howdy, Tel.<br /><br />Welcome to iboats. <br /><br />Hmmmm. Suppose an ignition part is getting a heat failure, but it takes a few minutes at WOT to get it hot enough to fail.<br /><br />Don't know much about the Tohatsu/Nissan engines except that they have a reputation for being bulletproof.<br /><br />I would determine which cylinder is failing; easy enough by just pulling plug leads, then troubleshoot the ignition for that cylinder.<br /><br />Take the bonnet off and apply a hair dryer to the ignition parts, one at a time, with it idling. When it drops rpm you have found the heat sensitive part.<br /><br />Good luck, and let us know what you find.

 

[telfish]

Re: Nissan NS70A2 problems

Thanks JB.<br /><br />It will have to wait til spring to try the hairdryer thing. Not sure if it's heat related as I have to leave it a day sometimes, then other times it will clear by itself by playing with the throttles. That made me think it was gas related. It's a bit of a mystery, my dealer had no clues beyond changing the plugs and making sure there was no water in the gas. Also when it's doing this I have taken the top off and moved the throttles by hand. This revs the motor but it's still rough running.<br /><br />Tel

 

[TOHATSU GURU]

Re: Nissan NS70A2 problems

Check the compression. If its okay. Clean the carbs and then take a hard look at the fuel system. Start at the tank and check the fittings, then work your way back to the fuel pump. If you can force a leak, then you are sucking air. If the prime bulb does not stay firm, then you have a bad check valve. If you still can't find the problem, then pull the fuelpump. After that, look at the electronics.

 

[DJ]

Re: Nissan NS70A2 problems

One thing I've noticed in this section, is that many times the wrong fuel connectors are being used.<br /><br />Many of them look very similar, yet there are slight differences.<br /><br />As an example, I just went through that with a Honda. The fuel connector looks identical to an OMC, yet is different enough to cause starvation.

 

[timbyja]

Re: Nissan NS70A2 problems

I know this will sound bad, but what exactly is a check valve, where is it, and what is it's function?<br /><br />I'm fighting a similar problem with my 55. However when I let it set for a few minutes, it may or may not run fine for another short period of time.<br /><br />I have ordered a new fuel pump and tank fittings. The current fittings on my tank are attwood OMC fittings.

 

[TOHATSU GURU]

Re: Nissan NS70A2 problems

The check valve is built into the primebulb and keeps the fuel from going back up the line to the tank.