exhaust manifolds have weird "burn" pattern in them?
 

so i pulled my motor in my '90 Baja 250 (454 Mag carbed with a bravo) to fix a leaking Y pipe from my silent choice and have decided to do some checking on the motor while its out, and do some minor upgrades like roller cam, rebuild the heads, ETC.

Anyway i got the exhaust manifolds off and saw a cylinder port on each manifold that looks way different then the others which is weird??? funny part is when looking inside the heads they dont seem to show as drastic a change in color as the manifolds do?? i compression checked on all cylinders and had about 5-8 psi total delta from highest to lowest so that is all good

so any ideas why they few ports look like this?

http://i246.photobucket.com/albums/g...a/IMG_3283.jpg

http://i246.photobucket.com/albums/g...a/IMG_3282.jpg

http://i246.photobucket.com/albums/g...a/IMG_3281.jpg

http://i246.photobucket.com/albums/g...a/IMG_3280.jpg

What do the spark plugs look like? Stock intake and carb? I think one of your problems were valve seals, but there is more to it then that.

cylinder 5 looks like it has a bad valve seal. that white color looks like its getting hot, too hot.

stock carb and intake on it.

i realize light colors mean typically mean lean, but why would only 2 cylinders look like that? the plugs looked good as shown below relative to the exhaust cylinder port they came out of. the plugs dont seem to exhibit the same really lean condition the manifolds reflect, those 2 cylinders look slightly lighter but still show a nice tan on the plug.

http://i246.photobucket.com/albums/g...a/IMG_3289.jpg

http://i246.photobucket.com/albums/g...a/IMG_3288.jpg

http://i246.photobucket.com/albums/g...a/IMG_3287.jpg

i put 10-12 hours on it this season and the oil level never dropped a touch, and its never blown a puff of oil on startup which is typical of bad valve seals isnt it?

if your basing the bad valve seal theory on the valves that looks wet i'm pretty sure thats from when i fogged the motor through the carb when i winterized it a few weeks ago, the stick might have been aimed right at those cylinders before i killed the motor? who knows, regardless its getting new valve springs and seals when i replace the springs so i guess it doesnt matter whether they are leaking or not!:ernaehrung004:

so anybody got any idea why only a few cylinders look lean in the manifold????:confused:

Are you sure it's just a few cylinders that are lean or did you add color to some when you fogged the motor. A vacuum leak at the port can cause a lean cylinder.

well the part i find strange is the spark plugs and ports in the cyl head dont seem to exhibit the drastic "lean" look that the manifolds do on those specific cylinders? i certainly agree a intake manifold leak would cause a lean cylinder, but my confusion is the manifolds looks to be telling me a different story than the plugs and cylinder ports do?:eek:

could be just the way it was run just before you pulled it apart, just started it up for a couple mins ??? full run session ?? etc....what temp when shut down ?

Wrong spark plugs,

They do have quite an extended tip. I don't think it would cause the variances though. What plugs are they????

Carbed engines will often run a little leaner in some cylinders, especially in the front and rear cylinders.

Exstened tip spark plug advances timing

champion RV15YC4 plugs in it, i have never changed the plugs in it, they were in it when i bought the boat. not sure why they went to this plug???

??? hows that possible?

my understanding was extended tips are to try to get more into the center of the chamber, and they also tend to foul less?

What carb and intake is on it and was there a carb adapter to go from a weber holley square bore bolt pattern to the stock gm spread bore if so that is your lean problem it is a
sh!tty set that mercruiser will do to make the cheapest set up to make it run. they did that with all the 330's

stock carb and manifold on it.

well heads are off, cylinders 1 and 8 are the leanest cylinders judging by the combustion chamber. i'm surprised how clean the chambers are for a 500 hour motor, actually everything on this motor is clean clean clean inside. bores look mint, still see nice cross hatching in them/ luckily no surprises have been found!:ernaehrung004:

http://i246.photobucket.com/albums/g...a/IMG_3336.jpg

gibson exhausts

anyone know about magnaflow, or kooks exhaust systems I was thinking of those?

Extended tip spark plugs bring spark event closer to piston, similar to timing advance.

Extended tip spark plugs bring spark event closer to piston, similar to timing advance.

+1 I have seen similar effect on circle track engines where the plug seat was machined deeper to more the plug closer to center. It does effectively "advance" the timing.
Sorry, didn't mean to hijak.
The light color holes do look a bit leaner, but the heads and ports look overall pretty good! By any chance you didn't happen to run a tank of race gas did you? Leaded fuel will give a white/grey color to exhuast when tuned properly.