Black on transom
 

Anybody have a trick to keep black off the transom and under the swim deck. I have applied wax multiple times, and even wiping down after words doesnt get it all off. Looking for something that keeps it off all together.

Im going to try the On Off cleaner that was recommended to me.. Heard its a pretty harsh cleaner though so dont use it on painted surfaces.

We have used duPont Prepsol for years. It is used as a final wipe for auto finishes. It removes all the soot and will it will not damage the paint or clear coat. You can find it at most commercial auto paint stores.

I got stuff to get it off. Just wondering if theres something out there that keeps it off to start with

any chance of fixing the rich idle so it doesn't do it ?

+1 Clean flame arresters ?? Air idle adjustments ??

I could try those we arent talking anything crazy here, The black is what I have seen just about on any boat.

not mine... and mostly carbed ones with exactly this sort of issue.

if yours is injected, make sure the thermostat is working properly and the water is getting to temp. if its carbed, make the idle misture correct and your problem will cease to exist to the most part. i know that is a broad brush suggestion... maybe your combination requires some crazy fuel curve that causes this but sending unburned fuel out the back isn't doing the internals of that motor any good at all.

x's 2...no carbon build up on my transom ever...something's not right with how your engine is running...

Tell us a little about your engine and what fuel brand and octane you are using and how your exhaust is configured. Maybe we can help with some explanations and ideas.

Best Regards,
Ray @ Raylar

91 454's rochester 4 quadrahejets. Gill silent choice exhaust, premium fuel. Engines were rebuilt before I had them about 60hours ago.. Its more of grey film underneath than black but is definitely exhaust stain. Carbs are being rebuilt as we speak.

boat is a fountain fever.

do you run the silent choice a lot ? that restricts the xhaust quite substantially and will make it have a rich idle...

probably 25% of the time.

I must add the exhaust pipes themselves arent black with soot. Could the oil pump be pumping to much? I did lost about 1/2 to 3/4 qt of oil after most of the summer of boating, but I dont think thats to off base

Mine used to get black, idle was wayyyy rich, leaned it out and no problems now.

When I read the title of thi thread, I thought for sure this was a 496........

which screw is the lean one?

On a Quadrajunk...I mean Quadrajet there are two screws in the base on the front of the carb that are the idle mixture screws. Back in the 70's/80's when I messed with them we would use a baseline of running them all the way in and then backing them out one and a half turns. We would then adjust in or out from there.

If they are stock engines with stock compression, then stop running premium fuel. It does not burn as completely and causes the black soot.

i can't imagine 1/2 qt over 20 or 30 hours or whatever your summer i is way out of line... there are so many things that could do this to you... first of all... that carb is a 40 year old design from the era when nobody cared much about anything ... how old is your actual example ? a lot of them had problems with the floats saturating w/ fuel and getting heavy or sinking which would make them do rich things in weird ways depending on load... that screw is just an air bleed if memory serves and won't change the actual idle fuel total... but i can't remember what drives the idle circuit on that carb... never the less...
its the same advice i always start with... start with the simple stuff... is the timing correct at idle ? are the temps too cold, have the plugs ever been changed ? all the simple stuff first. has the carb ver been looked at and jetted by someone that actually knows what they are doing and not just watched 3 episodes of hot rod TV ? how about cleaning it virgin and doing a complete trip and never use the silent choice and see if that answers your question ... i suppose it just comes down to how much it bothers you vs how wrong it really is that will determine how much time and effort you spend chasing it... but if it IS legitimately rich, then you are wearing out the motor prematurely for sure...

I have twin 496Mags, and have black on transom... tell me how to fix!

have silent choice but almost never run it, strait tips for the load side. bone stock 496Mags, 160-170 hours on them

I have been running 87 octain in it.

+1 on switching to 87 fuel unles you need the higher octane due to higher compression. I had a 1999 454mag EFI stock and thought i was doing myslef a favor running 93 fuel, transom was always black. switched to 87 and 90% of the soot dissappeared.

Both my Fountains are terrible at this. Just a couple minutes of running and it's black. Tried different fuels, plugs. Nothing.

Having the PCM's reflashed is about the only way.

the engines were rebuilt 2-3 years ago, carbs are rebuilt as of last night. Guess I will run 87 and see what it does from there. I saw the receipt from the rebuild and the cap and wire were replaced so Id have to imagine the the plugs were replaced. I guess it could be a possibility that upon rebuild they set it to run rich and set it back right either. Thanks for all the help.

What do they need to fix with a flash/tune? just the idel mixtures? who in the northern alabama areas does it? how much does it cost?

If this has carbs, what needs to be flashed?

think they were talking the 496

My 496s have always sooted up the transom. Nothing horrible, but noticeable. Just the nature of the beast. Have you tried using a good polish? I use Nautical Ease boat polish and it seems to make the soot wipe off a little easier.

A product called Roll Off. You can get it at West Marine.

Whipple can do it for sure and maybe Mark Precision Marine. They change the settings in the PCM.
I think Mercruiser has a factory reflash for the PCM as well, but pretty sure the PCM's need to sent into Merc as well.

Besides the mechanical aspects of the creation of the soot, read up here, wipes right off.

http://www.offshoreonly.com/forums/3658736-post50.html