NS3.5 won't start - carb question

[68SeaShark]

Hi Guys - hoping someone might be able to help me.
I have a 2003 Nissan/Tohatsu 3.5 that I can't get started.
I have replaced both the coil and CD unit modules with new parts and am definitely getting spark.
Every once in a while I will get it to fire briefly (short cough), but typically it does nothing but wear my arm out.
I measured the compression and it is holding at 60psi - I'm assuming this is ok.
I hear air whistling through the choke plate of the carburetor when I pull the starter and when I remove the spark plug after pulling for a while it does have some amount of gas on it - I'm really not sure how wet it should be.

Given that I've changed the coil and timing modules, the only other thing I can think of is the carb.
I have taken it apart and cleaned it multiple times. I'm wondering, though - there are two small holes on the underside of the carb body (not main jet or float needle - see picture below) - I can blow air through the left side hole and it will exit through the hole just behind the choke plate (see second picture). If I blow air through the right side hole on the bottom of the carb body, however, it appears to be clogged - is this expected or should this hole be clear?

I'm open to any suggestions that would help me get this thing running.
thanks,
Kevin

 

[pvanv]

Re: NS3.5 won't start - carb question

60 psi is quite low. Still, I would expect it to run, even if poorly. Have you checked the exciter coil with an analog ohm meter? The hole in the carb casting is a bowl vent. As long as the float height is OK, and the needle is seating well, the carb should at least operate, assuming you completely disassembled it and soaked it well in real carb dip. A wet plug is an indication of not firing. You could verify the magneto key hasn't sheared.

 

[Sea Rider]

Re: NS3.5 won't start - carb question

You should pull rope 4 times minimum with throtle opened to max to have a reliable psi reading, 78 psi is the standard reading in opt conditions, check small fuel **** inside filter for obstruction, probably bit clogged not letting sufficient fuel into the carb/cylinder. Check internal plug contact if not corroded/ good condition.

Happy Boating

 

[68SeaShark]

Re: NS3.5 won't start - carb question

I measured the compression again - pulling the rope with the throttle wide open. First pull I get about 30psi, second and all subsequent pulls I can get it to a max of about 65psi but no higher. Would this cause the motor not to fire at all?

I did go back and check the fuel **** filter and it was clean. I cleaned it and the fuel tank out anyway just in case. Still, I can't get so much as a cough out of it when I pull.
I am definitely getting a nice blue spark. Is it possible the spark isn't strong enough? Could this be caused by a weak exciter coil? Keep in mind that my ignition coil and CD modules are both brand new.
I haven't ohmed the exciter coil, but I can do so easily - what should I expect to read? Guess I should pull the flywheel and have a look.....

 

[pvanv]

Re: NS3.5 won't start - carb question

The hot blue spark is correct, so the exciter is likely OK. You could have a sheared or missing flywheel key, which would have you firing out of time, or you could still have a gunked-up carb passage. Is the float set correctly?

 

[Sea Rider]

Re: NS3.5 won't start - carb question

If flywheel key it's ok, what about spraying some fuel directly on carb's throat and pulling rope, if starts well, probably carb still with issues ? That carb has a fork & float, check fork's sides are parallel to each other & seat needle valve entrance is clean. Plug should be 1.0 mm tight gapped. If all tested parts are ok, when engines are low on compression are sometimes difficult to start, the only solution change piston rings for another standard size to extend cylinder life or go for a 0.5 mm piston/ring kit if too much wear is detected on cylinder wall.

Happy Boating