1998 Volvo Penta 3.0 misfiring on plugs 3&4

[ExtremeCheese]

I have a 1998 volvo penta 3.0 and it appears to be misfiring on plugs 3&4. I think this because it has a rough idle and the plugs are fouling out (i think) after 5-10 minutes of use. I pull them out and they are wet with gas and completely black. I have checked for a spark and its there on both plugs.
What ive done so far:
Rebuilt carb
New ignition coil
New ignition module
New plugs and wires
New dist. Cap and rotor
I have NOT had the timing set, waiting for mechanic.
Is there anything else that could cause this problem? Thanks in advanced.

 

[Scott Danforth]

What is compression on all 4 cylinders?

 

[ExtremeCheese]

What is compression on all 4 cylinders?

All four were getting around 150

 

[alldodge]

It runs fine for 5-10 minutes, then it starts missing and plugs 4-5 are black and wet. Plugs 1-2 look fine (cream color or brown). Compression is around 150 on all cylinders.

Something listed above is not correct
Even if the firing order was not correct would not produce what is listed

 

[ExtremeCheese]

It runs fine for 5-10 minutes, then it starts missing and plugs 4-5 are black and wet. Plugs 1-2 look fine (cream color or brown). Compression is around 150 on all cylinders.

Something listed above is not correct
Even if the firing order was not correct would not produce what is listed

I dont know what else to add…thats whats happening.

 

[Scott Danforth]

a cheap aftermarket distributor cap with bad terminals could cause cylinders 3&4 to loose spark after a while

so could not having the plug wires seated all the way on the plug or cap towers

 

[ExtremeCheese]

a cheap aftermarket distributor cap with bad terminals could cause cylinders 3&4 to loose spark after a while

so could not having the plug wires seated all the way on the plug or cap towers

I doubled checked the wires, they were seated correctly. I dont think the dist cap is cheap, although im not sure what the brand is. It was ordered through Oreily auto parts.

 

[alldodge]

Get a spark gap tester and one by one install and see if its white and can jump the gap. Can get them about anywhere

https://www.amazon.com/Thexton-THE404-Spark-Tester/dp/B0002STSBM

 

[ExtremeCheese]

Get a spark gap tester and one by one install and see if its white and can jump the gap. Can get them about anywhere

https://www.amazon.com/Thexton-THE404-Spark-Tester/dp/B0002STSBM

I will try that, thank you!

 

[kenny nunez]

Your exhaust manifold riser could be the problem leaking back just enough exhaust water to foul the spark plugs.