Popping through the exhaust
 

Engine runs fine otherwise and pulls as strong as the other. However, at idle it pops out of the exhaust every once in a while. Ignition?

These are carbed 509s with 1050 dominators with MSD Ignition.

Re: Popping through the exhaust
 

If you are popping out of the exhaust you are most likley having a problem with the exhaust valve, sticking, warped, or a stickey lifter on the exhaust valve.

Re: Popping through the exhaust
 

If it is otherwise running fine you could be getting some cross firing between cylinders. Try some new plug wires or at least make sure they aren't too close together. Especially watch 5 & 7!! If 7 fires from a cross fire on 5 you will burn down #7 due to grossly over advanced timing. If you have the firing order goofed up you could hear some popping out the exhaust, but it would likely not run very well, so that probably isn't it.

Re: Popping through the exhaust
 

check for a water leak in the exhaust.

Re: Popping through the exhaust
 

A quick compression and leak down test would'nt hurt.

Re: Popping through the exhaust
 

I'm going to check the ignition and do a leak down this morning. I'm thinking, hoping, ignition. Since it's the odd side (1,3,5,7) it will easy to get to. It's not a constant pop, it varies every 10 seconds to a couple of minutes. When I got the boat back to the lift it didn't pop at all.
There was also a lot of condensation in the engine compartment when we headed out. After the engines warmed up a little I throttled up to 3000 rpm. After about a minute or two one motor just seemed to come to life and ran up to 3500. About 20 seconds the other just popped up to 3500. It ran fine for the rest of the time we were out except when we slowed down to come into the river, the one motor ran a little rough and would pop every now and then.

Re: Popping through the exhaust
 

This sounds way too familiar. My problem turned out to be a valve. Hopefully yours may be ignition/fuel related. Not too many weeks left here in "snow country.

Re: Popping through the exhaust
 

Turned out to be ignition. The cap was way over due for a change, people were laughing when I pulled it off the motor. So while I was at it I did the cap, rotor and wires on both motors (all MSD) . Then lost a coil on the other motor yesterday. I carry spare everything but didn't have a coil. First time in 10 years I had to idle all the way home on one motor.