Hey guys,
I'm running a pair of 97' HP500 carbs and it literally soots up the transem within 2 minutes. The engines run great! They seem to idle a touch rich. Other than that I have changed plugs, cap and rotors. I have tried different octane fuel and they all seem to soot. Is there any other adjustments I need to do? Or do I have to live with this problem.
Thanks

Is it just at an idle or while running as well.

For Idle I would look at adjusting the air mixture screws. For a leaner idle.

For running you would need to change jetting.

Has it always done this or did it just start? If it just started might be time for a good rebuild on the carb.. How many hours on it?

I just bought the boat this year. I knew the previous owner and he said it has done it from day one. He also said he noticed it was worse with higher octane fuel which makes sense. I have not done a plug reading after a run yet. I know it is mostly caused at idle. I should probably check the float levels, but on the other hand it never bobbles or floods. Maybe I should just paint the transem all black

when one of my motors had that problem I found a leak between the intake and the block.

What octane fuel are you running? If you are running premium fuel that could be most of it. I believe you should run 87 octane. My boat soots up quite a bit even running the 87 octane. Just before I went out last weekend I changed my oil over to a Mobile 15/50 synthetic and I used almost 200 gallons of fuel over the weekend. When I took the boat out, it was the first time it was not heavily sooted. It was actually almost clean. Not sure why. Didn't know if the synthetic had anything to do with it either.

I agree I would try regular fuel first. If that does not work, lean out the idle a little by turning the air mixture screws in a bit. You can adjust them for higest vacum or turn them in until the motor starts to stumble then turn them out a half turn. That will get you close.

Idle air screws need adjustment if it occurs at idle. Adjust for maximum manifold vacuum.

You might be burning oil.

I think I have heard too many 502's do the same to think you are alone or have a unique "problem" besides a grimy transom.

I had the same deal with 350 Magnums and Mercury said it is a rich idling carb. Changed from the Holley/Weber carbs over to Edelbrock carbs using a simple adapter plate and the soot was gone; the boat started on the first try and gained 2 mph.

My biggest concern was carboning up the engine over time.

The Higher Octane Fuel,the Cooler The Burn/the Lower, The Hotter The Burn.87 Burns Hotter Than 93.sounds Like A Rich Problem,try Adjusting The Idle Circuit,the Small Screws,turn Them In Until The Idle Changes,then Out A Quarter Turn,soot Is Unburned Fuel,you Might Want To Try A Hotter Spark Plug Aswell,generaly The Lower The Plug Number (mr41t)is Going To Be Cooler Than A (mr43t). Soot Happens Though,good Luck,OH YEH,CHECK YOUR TIMMING