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70hp bogging down at higher speed .......

M

mainer

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Hi - Used 70hp Nissan, 1990. Ran fine first two trips out. Now will not run above 1/3 throttle. Have replaced in-line water separator, cleaned fuel bowl, and cleaned fuel strainer. Also replaced the plugs. Still doing the same thing.

I am not a mechanic but can take thing apart and put them back together. There is a rod with a ss piston surrounded with a wire core on the starboard side of the motor...... it appears to open the carb ports for more air (?) when the throttle is advanced. When I observed this mechanism yesterday on the ocean, it did not move when I increased the fuel. When the motor started acting up, I thought it was being starved of fuel....... now I'm thinking it might not be getting the air mixture it needs for the increased fuel supply????? Also, what do you call that piston/wire core assy??

Anybody out there have a thought? Model is NS70A2 ..... 1990.

Thanks for any ideas!! Steve in Maine
 
I take it you have a remote model (EP type). That coil should be the electric choke solenoid. Verify that it clicks shut when you press the push-to-choke feature of the key switch, and releases when you release the key. You could have a number of issues, but likely fuel problems. Start with Fresh fuel and your trusty Factory service manual. If the carbs are not run dry at the end of every day, you could likely benefit from a carb removal, disassembly, cleaning, and then a sync when the carbs are reinstalled. If the idea of a thorough carb disassembly and 4-hour soak in a carb bath are daunting, get thee to a dealer.
 
Paul - Thanks for the quick reply. This boat is also 1990, with an internal fuel tank. Like you, I suspected a fuel problem. Interestingly, the problem started just after I'd filled the tank to capacity for the first time this year. The boat is new to me as I bought it in December this past year. It's quite possible the fill dislodged a bunch of crude that's been built up in the tank....... I'll try the choke and let you know.

Again, thank you for the reply. Steve
 
Paul - Just checked choke and it is operating properly ..... just as you said. Also, this Nissan is the remote model. Time to tackle the carbs...... Steve


pvanv said:
I take it you have a remote model (EP type). That coil should be the electric choke solenoid. Verify that it clicks shut when you press the push-to-choke feature of the key switch, and releases when you release the key. You could have a number of issues, but likely fuel problems. Start with Fresh fuel and your trusty Factory service manual. If the carbs are not run dry at the end of every day, you could likely benefit from a carb removal, disassembly, cleaning, and then a sync when the carbs are reinstalled. If the idea of a thorough carb disassembly and 4-hour soak in a carb bath are daunting, get thee to a dealer.
Click to expand...
 
Just wondering from your comment, " If the carbs are not run dry at the end of every day,", how does one do this? I have heard it is not good to disconnect fuel lines as air or debris can be a problem. Yes? No? Or perhaps there's another way?
 
...... carbs are being disassembled, cleaned and put back together...... I'll let everyone know what happens ....... Mainer
 
Thanks tohatsu_guru. Do you agree with running carbs empty each time you take it out? I think it was pvanv that suggested that procedure and I've not heard that before. Certainly gas can't be destructive to carb parts inside of a month can it?
 
Of course you may not be aware of the rush hour traffic at the ramps around here. If I were to do that I'd have some pretty unhappy campers and they don't mind saying so out loud and in your face. You know the odd thing is it is never the guys in the little boats, they almost all seem to pretty nice guys. But good advice cause we can certainly do this once home. Thank you
 
Around here, my usual advice is to disconnect the fuel line when approaching the dock. Then the motor idles as you get the trailer ready, or tidy up the boat, or tie up to the dock. Then it runs dry without using any additional time. Multi-tasking as it were:)
 
I think if I were going out on weekdays, that might on a very few occasions work out On Golden Pond, but we have far too many boaters in far too little water, and I'm one of them, LOL. We were patiently waiting for an older gentleman not long ago to get his boat running and out of our way, he was taking up space so I couldn't launch, and my Son & I offered to help, when Mr Rudeness leaned into the conversation by hollering "Come on guys I've only got two hours to fish" Now I'm thinking 'And it's my fault you're late?' But that's just how some of them are.

I get by your description that a motor may run a few minutes using up what's in the line & carb bowls. I'll give it a try soon.
 
Good ol' Mr. R... Yes, we have a few of them here. I usually don't bother wasting any time or effort addressing those idiots... I just let them simmer in their own juices. More entertaining that way :)
 
Hey guys - Quick update on the 70 hp Nissan. Cleaned carbs just like Paul suggested ... worked like magic! Back on the bay and running like it's new! Thanks so much for all the suggestions and help. This engine is on a 16' Wahoo and it's like driving a convertible auto compared to my 21' Chris Craft (cuddy). Thanks again!!! Steve in Maine
 
Hey that's great news Mainer. Did you do this yourself? And if so, can you estimate total time, rough estimate, from opening service manual to placing cowling back on? I think I may have to do this also. Though my problem is different. Thanks
 
Hello Fishn4funn - The last carb I rebuilt was on a 73 VW & then ended up having it prof done ...... that was 30 years ago! I went to a local friend of mine. He charged me for 2 hours. It wouldn't surprise me if he actually took longer than he charged me. Sorry I can't help you with what it took for a lay person to do the job. Good luck with your project. I will surely be keeping this site book-marked!!!

Thanks again everyone. Steve in Maine ....... Casco Bay Islands
 
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