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brown smoke

luhrs_40

Contributing Member
89 crusaders 454 around 2200 hours compression decent less then 12 pounds between cylinders
we troll alot Around 500 hours between engines, Notice half way last summer coming back from fishing
when cruising over 2800 RPMs both engines will smoke a light dirty brown smoke. Its not steam or oil
Any ideas? Check the timing and change the plugs no difference
 
I've never heard anybody use the 'light dirty brown' descriptor before.....

If its not oil, the more likely option is fuel.....has the fuel consumption rate changed?

@ 2200 hours, even though the compression appears satisfactory, it is very probably that the top ends are worn out...1000 operationg hours was the expected value back when I worked in the shop daily.....you are well over twice that....
 
Engines still running good From oil change to oil change there is no oil missing
Smoke looks like carbon? mixed with fuel and mostly when the advance kicks in around 2800 rpms
We troll 90% and cruise 10% of the time
And yes plugs are black after couple runs
 
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Ayuh,..... When excess carbon is blown outa the tailpipes, it's a reddish brown color,.....

Check the spark plug colors after a long troll to see what's up,......

Introducin' water into the combustion chambers, while runnin', will cause the excess carbon to be cleaned from the cylinders, 'n piston crowns too,.......
 
Is it safe to put water through the carb while engine running?



Ayuh,..... I've been decarbonizin' motors that way for quite a few decades,.....

Learned of it from an old British Land Rover manual,......

With a warm motor, in neutral, run it up to 'bout 1500 rpms, 'n dump a soda bottle of water down the carb's throat,....
If the motor labors terribly, yer pourin' it too fast,....
If yer not hearin' the motor labor, at all,.... pour it in abit faster,.....

When yer doin' it Right, the brown cloud behind the rig will be very obvious,....
 
Napa also sells a pray that will do this. Warm up the engine. start praying it in the carb keeping the engine running and when the can is empty shut her off. Wait for the recommended time then start her up. You are going to blow a lot of smoke so I would suggest not doing it next to another boat. Amsoil makes a great product for this also.
 
Going back to the brown smoke at cruising speed, assuming that you have carburetors, could it be that they are supplying too much fuel? Are they Quadrajets? If so, they may have leaky bottom casting plugs, or they may just plain need rebuilding.

Here's a description of the bottom plug problem: https://www.hotrod.com/articles/hppp-1107-home-remedy-quadrajet-carburetor/

If these are the original carbs, whatever you do, don't exchange your existing carbs for rebuilt carbs. If you do, you will surely end up with automotive carbs that have been butchered to become "marine" carbs.
 
Please don't condemn the well plugs on a quadrajet, especially if they have 170xxxxxxxcasting numbers....they rarely leak (unless abused). the early 70 casting numbers only had the brass plugs which spawned the issue and I can't say I've seen one of those on a boat in the last 35 years....
 
Please don't condemn the well plugs on a quadrajet, especially if they have 170xxxxxxxcasting numbers....they rarely leak (unless abused). the early 70 casting numbers only had the brass plugs which spawned the issue and I can't say I've seen one of those on a boat in the last 35 years....

That's good to know about the well plugs, Mark.

Since the OP says the smoking happens at 2800 RPM and above, could it be related to the secondaries kicking in and providing too much fuel?

Just trying to stimulate some discussion about the cause. :)

Dan
 
no issues here...

That's why I asked about a change in fuel consumption.....

The secondaries should not be open @ 2800 RPM...if they are, there's likely an issue with the air valve controls....
 
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