Nissan ns40c midrange issue..breaking up

[Trilogyinc]

Hello to all! This motor is eating me up. Nissan NS40C. Starts easy..idles fine..give it the juice and it just breaks up.it has gotten on plane a few times but not lately. It doesn’t seem to bog just pops and sounds like it’s overloaded. New battery, new cdi, new plugs, carb has been gone through about 6 times now, timing is set by the manual, I decarbed the motor also. Changed fuel pump thinking it might be leaking in the crankcase. It does it with a 10 pitch prop and the 15 pitch I tried.. I just ran it and I’m about to pull the plugs and check compression again. And if you hit the choke when its breaking up it will turn off. Thanks for any help someone might be able to give me.

 

[Trilogyinc]

[No message]

 

[Trilogyinc]

Compression with my tester is 90 each cylinder but idk how accurate my gauge is.

 

[Trilogyinc]

[No message]

 

[pvanv]

Popping through the carb is usually too lean or over advanced timing.

 

[Trilogyinc]

Thanks Paul. Is that paint mark TDC on the pic I posted? My service manual isn’t the best help. I can find tdc by pulling the plug but not knowing for sure on that arm may be my issue since it’s independent from the flywheel.

 

[Trilogyinc]

I know the paint mark(triangle) is tdc from pulling a plug and using my timing light. What I don’t know is what the marks are..as in degrees..2? 5?...any help is appreciated
may manual isn’t helping

 

[pvanv]

I think the long marks are 5 degrees, if memory serves.

 

[Trilogyinc]

Back out today after some timing adjusting. Still crackling some but it planes out now. You can work though it chopping the throttle a bit. Guess I’ll keep playing.

 

[Trilogyinc]

[No message]

 

[Sea Rider]

Factory states 107 PSI on both cylinders with a healthy pressure gauge. Factory 40 C timing advance is 25º.

Set the throttle grip to min side, engage forward gear and full throttle to max, check if the timing plate marks has stopped at 25º at the middle of both mating surfaces as shown...



If not, with throttle grip remaining at its max position, release the Joint upward, advance the timing plate right or left to dial 25º, adjust the bar gap distance as required for the timing and mating surfaces to match.

Happy Boating

 

[Trilogyinc]

Sea Rider I had it set like the manual says and your picture shows. I was hoping the lines were 5 degrees. The boat did get up on plane today..everytime..but it’s still breaking up. It’s only midrange..idle, putting and wot is great. Not sure about the pilot screw but it didn’t seem to make a difference moving it in or out but it’s set at 1-1/2 turns from seat. The timing plate has to be accurate because it is dead on tdc with my timing light.

 

[Trilogyinc]

Worked through my timing issue this morning out on the water and now there’s a new issue lol..after running wot for a minute the motor will completely die like it lost spark. Cranks right back up get back on plane to wot and it will do it again. It has a new cdi unit but old exciter and trigger coils. I’m not sure if something is getting hot and breaking down or not. Any thoughts?

 

[Sea Rider]

Each vertical mark past 0 is + 5º, +10º and so on. Have set all my 2 strokes motors to 0º when the throttle rests at min side by turning the idle screw bit CCW to lessen the higher rpm that setting achieves. The throttle response is much better at full grip. If the motor is experiencing unusual behavior seems to have an erratic electrical component which heats up, shorts, kills the motor, to works OK once cooled to miss shortly after and so on.

If already counting with a new CD, should be an Exciter, Pulsar or Ignition coil failing, the bummer is which one ? To replace all 3 is around $ 200.00 to avoid the wild guessing or if wanting to find the direct less costly culprit perform an Ohm and DVA volt electrical troubleshooting test on all 3, one must be altered ? Those electrical components usually misses at higher rpm when the motor requires the max power out of each one.

BTW, the (fuel/air) pilot screw only works at min idle rpm for the motor to rev smoothly once carb has passed idle, the carb works with the fixed jets..

Happy Boating

 

[Trilogyinc]

Sea Rider yes sir I agree on the electrical issue and I thought I remember reading it did bypass it at a higher rpm.I did put a new cd unit on it. I actually bought a pulsar and exciter coil also but neither fit it, which was upsetting btw. I did a resistance check on them and the pulsar coil is 10 ohms below what my manual specs. Exciter coil is spot on. Alternator coil isn’t being used but it is ok. The pulser coil they sent is to tall and the exciter coil is to wide. I probably wouldn’t be tying this if they fit lol..but who knows..thanks for the responses!

 

[Sea Rider]

Would be much better to check the exciter coil with a DVA meter to check its voltage output while cranking the motor. Check the DVA factory specs for it. Sometimes the Ohm resistance doesn't say much, that's why having 2 different electrical troubleshooting tests. Try to get the original size for both exciter and pulsar coils...

Happy Boating