Crusader 454 raw gas in exhaust stream

I have twin crusader 454s in a 1987 Bluewater 51 with 1500 hours on them. Both engines run perfectly at all speeds. The port engine is producing a lot of sheen in the water as raw gas coming out of the exhaust. I noticed last year that the port engine had soot on all 8 plugs rather than the tan/grey look on the tips that they normally have after 100 hours of use. This engine burns about a quart of oil in 40 hours of use. The engine runs very smoothly at idle and at cruising speed and never stalls on docking.

In trying to solve the problem, we had the automatic choke replaced in case it was not opening properly. No change. My mechanic noticed the carb had some bubbling of gas at idle as seen from above looking down into the throat of the carb. My mechanic (lots of experience) suggested using a kit to rebuild the carb. There was no change. In case there was something wrong in the first kit, he rebuilt the carb again with a new kit. No change. We then had the carb replaced with a factory rebuilt carb and still no change in the gas sheen coming out that exhaust. Any ideas?

Check out my thread from a few years ago. Also do as earch on Rochester carbs and thousands of posts will come up. Just quickly, was the needle valve replaced the second time(or even the first) a bad needle valve caused my plugs to foul within 20 minutes of running. I see you bought a new carb and it did the same thing so probably not the seat. Maybe a low vaccuum issue.

http://www.marineengine.com/boat-forum/showthread.php?t=282890

Yes the needle valve was replaced both times and I assume in the rebuilt carb all was replaced as well.

Thanks, I did read your thread. Did you have excessive raw gas in the exhaust water as part of your problem?

Yes. I still do with the choke on. Once that opens I'm fine. Are you getting that gas in the water after warm up as well, or just with the choke closed?

Yes, after warmup and with the choke off we still get raw gas in the water.

when you look down into the primaries, with the engine running, if the fuel is coming from the main nozzle, you are experiencing what is called "nozzle drip". On a big block, the nozzle drip can be caused by a few different things. The most common is high idle rpm - what is your idle RPM, over 600?

You can verify that it is nozzle drip by warming up the engine and then backing off the idle speed screw. typically, when the drip become significant, you will "loose" the control afforded by the idle mixture screws. That is normal and to be expected.

Both engines idle at about 620 rpm. I will check this out. Since my last post I had the carbs switched from the port to stbd engine and vice versa. The port engine still appears to have the same problem of excess gas in the exhaust water. The starboard has a little but not like the port engine. We had a lot of wind at the docks with disturbed water today when I checked it and I will have to look at it on a more calm day.

One person said he wondered if there may be an electrical or voltage problem to the plugs since the carbon build up on the plugs was pretty uniform when changed last year. The spark plug wiring has never been changed to my knowledge. The points were changed to electronic ignition in 2001. Nothing else was changed.

Just for added info, the boat has always been on fresh water on lake Champlain and we don't have any of the corrosion problems we see on boats coming in from salt water.

It sounds like you have a plug not firing. Have you done the Fastjeff distributor test? To wit:

1. Warm the motor thoroughly and idle it at 1,500 rpms

2. Using insulated pliers and gloves, remove one wire at a time from the distributor and listen to the rpm change. All 8 should slow the motor noticeably. If one doesn't do it, leave that wire out and see why not.

Jeff

PS: A marine engine with rigid motor mounts will run with a cylinder out without shaking, as a car engine would. They can fool you!

I wil check to see if a plug is not firing as you suggested.