79cj7stone
New member
Nissan NS30A3 short shaft. 30hp, 2 cylinder, 1 carb
Issues: Anything over a slight increase in throttle from the start position when in gear and under a load, the engine bogs. Seems to run fine and will reach higher RPM when on muffs.
What I have determined so far:
Engine sat for probably 6 plus years in a barn. Pulled carb and cleaned. All ports were surprisingly clear. Reinstalled and engine fired up. Took on test run and encountered the issues above. I found a mouse had gotten in to the wiring harness and had chewed some of the insulation off the wires but did not damage the copper. Those have been taped up for the time beings. The main 2 were the red exciter wire and the the black and yellow wire off the coil. I verified resistance between the red and black and got 250 ohms and blue and black and got 37 ohms which is within spec on a CDI electronics sheet. Ground wire was also bare, so I replaced that.
New plugs were installed. BR7HS-10 gapped to .35 and issue is still present.
I put a inline spark tester (just the light blub one) and I am getting a light to each cylinder. I am planning on getting a spark gap tester today, setting it to a 7/16th gap and testing again. When I pulled the plugs, the top plug looked to be burning decent and the bottom plug looked like i just took it out of the box. Reinstalled the plugs and pulled the wires will running. I pulled the bottom plug wire, engine stumbled some but continued to run. I pulled the top plug wire and engine immediately dies. To me this means a lack of combustion in the bottom cylinder.
Compression check using electric starter: Top 80 psi and Bottom 80 psi
Compression check using pull cord: Top 88 psi and Bottom 88 psi
I am struggling to find a spec on the required cylinder compression. Anybody have that?
So I have unofficially verified spark, verified compression even though I think this is on the low end, so now I'm on to fuel.
Couple questions:
I believe this is a wasted spark ignition. Could I only be receiving primary spark on the top cylinder and wasted spark on the bottom cylinder and no primary spark on the bottom making it look like I am getting spark but in reality I'm not. I a little weak on this ignition system.
Could a weak fuel pump be causing fuel to the top cylinder and not the bottom?
Is the reed valve the only other possible blockage for this condition? On engine fuel filter screen is clear.
Any other possible ideas on this?
Issues: Anything over a slight increase in throttle from the start position when in gear and under a load, the engine bogs. Seems to run fine and will reach higher RPM when on muffs.
What I have determined so far:
Engine sat for probably 6 plus years in a barn. Pulled carb and cleaned. All ports were surprisingly clear. Reinstalled and engine fired up. Took on test run and encountered the issues above. I found a mouse had gotten in to the wiring harness and had chewed some of the insulation off the wires but did not damage the copper. Those have been taped up for the time beings. The main 2 were the red exciter wire and the the black and yellow wire off the coil. I verified resistance between the red and black and got 250 ohms and blue and black and got 37 ohms which is within spec on a CDI electronics sheet. Ground wire was also bare, so I replaced that.
New plugs were installed. BR7HS-10 gapped to .35 and issue is still present.
I put a inline spark tester (just the light blub one) and I am getting a light to each cylinder. I am planning on getting a spark gap tester today, setting it to a 7/16th gap and testing again. When I pulled the plugs, the top plug looked to be burning decent and the bottom plug looked like i just took it out of the box. Reinstalled the plugs and pulled the wires will running. I pulled the bottom plug wire, engine stumbled some but continued to run. I pulled the top plug wire and engine immediately dies. To me this means a lack of combustion in the bottom cylinder.
Compression check using electric starter: Top 80 psi and Bottom 80 psi
Compression check using pull cord: Top 88 psi and Bottom 88 psi
I am struggling to find a spec on the required cylinder compression. Anybody have that?
So I have unofficially verified spark, verified compression even though I think this is on the low end, so now I'm on to fuel.
Couple questions:
I believe this is a wasted spark ignition. Could I only be receiving primary spark on the top cylinder and wasted spark on the bottom cylinder and no primary spark on the bottom making it look like I am getting spark but in reality I'm not. I a little weak on this ignition system.
Could a weak fuel pump be causing fuel to the top cylinder and not the bottom?
Is the reed valve the only other possible blockage for this condition? On engine fuel filter screen is clear.
Any other possible ideas on this?