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Carbon build up on the backside of valves is common and normal with aging of the engine. Other than having been in service a long time it isn’t necessarily an indicator of trouble, though it can be.

Oil leaks around valve stem and seals especially on the intake make for a lot of crud on the backside of the valve. The exhaust is very hot and steel loves to bond with carbon so those valves get coked up especially if the engine is burning oil. The problem with deposits on the exhaust valves is it causes them to run hotter which eventually will burn them.

Coolant leaks into the port system generally leaves clean valves.
 

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Discussion Starter · #22 ·
Carbon build up on the backside of valves is common and normal with aging of the engine. Other than having been in service a long time it isn’t necessarily an indicator of trouble, though it can be.

Oil leaks around valve stem and seals especially on the intake make for a lot of crud on the backside of the valve. The exhaust is very hot and steel loves to bond with carbon so those valves get coked up especially if the engine is burning oil. The problem with deposits on the exhaust valves is it causes them to run hotter which eventually will burn them.

Coolant leaks into the port system generally leaves clean valves.
my engine only 20 hours run .and most engine I work on I saw exhaust valve like ( pink color on them) not like my exhaust valve dart black oil build up ,
 

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I saw air leak in to water almost intake and exhaust valve leak ... I bring to machine shop they cost me 350$ to re work on cylinder head ... and I am not do it ... I took cylinder head home clean it up and install back to engine with new gasket ... engine idle good ... ,but I fell I did not get all power from 383 . I think some thing go wrong to my cylinder head
Are you saying you did NOT have the shop fix the leaks?
Do you have the tool to change bent valves by yourself:
Valves don't cost that much:
CP, Stainless Racing Valve, Chev SB, 2.020" (Intake), 11/32", 5.025" (+.100") - Competition Products
The vacuum secondaries of the carb. may also be a problem...
Your carb. may also have a blown out power valve causing black head valves...
Also leaking valve seals in the heads...
Your cam won't have a smooth idle, but a lopey idle...
There's probably just a small problem somewheres that you need to find... maybe someone local to you can help you... where are you located? We have 150,000 members...
 

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Discussion Starter · #26 ·
Are you saying you did NOT have the shop fix the leaks?
Do you have the tool to change bent valves by yourself:
Valves don't cost that much:
CP, Stainless Racing Valve, Chev SB, 2.020" (Intake), 11/32", 5.025" (+.100") - Competition Products
The vacuum secondaries of the carb. may also be a problem...
Your carb. may also have a blown out power valve causing black head valves...
Also leaking valve seals in the heads...
Your cam won't have a smooth idle, but a lopey idle...
There's probably just a small problem somewheres that you need to find... maybe someone local to you can help you... where are you located? We have 150,000 members...
not carb i send out for they rebuild last month, I for sure valve leak at valve seat .
 

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not carb i send out for they rebuild last month, I for sure valve leak at valve seat .
The proper carb. secondaries opening rate adjustment can only be done by testing/experimenting on the running engine in the boat...

Also, Eddy carb.s flood over if fuel pump pressure is above 5 psi... which many stock pumps are...
.
 

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what curtis andbogies said are very good points.
fresh water only then use aluminum heads or if cooling system is closed.
I would use a solid roller cam with specs like they use in the LS 427.
LSA at 115º or more. 204-210º duration. .58 valve lift with 190-195 cc Profiler heads.
750 cfm on an rpm intake (850 if the air cleaner system is restrictive)
headers with 1 5/8s long tubes.
if you cannot use a header then you will need a little more exhaust timing
9.5:1 to a max of 10:1 CR
steel crank/quality rods, super precision balance
For starters, it's a 17' boat. using your solid roller that big will ause reversion, which is a motor killer. It will pull water from the risers and hydro lock.
 

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I was use stock vortec head it make great power but it is iron it heavy ,that why i bought this cheap aluminum head . it make my engine weak the boat hard to get on plane .my boat is 17 ft it is I/O boat run 23 p impeller i read on line lt4 hot cam is same XM270HR . My 383 run lt4 hot cam does not reversion water to engine.
Go back to the vortecs and be done. The weight difference you aren't going to notice unless you are overloading the boat in the first place.
 

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The L31 head is each about 20 pounds heavier than aftermarket aluminum, not as much as you would think. So the total difference is only 40 pounds. Even the factory cast aluminum heads like the L98 and LT1/4 head’s are thin castings so are quite light compared to aftermarket aluminum heads. So the OEM head’s compared to aftermarket aluminum which use a thick wall for greater durability in high performance use do not show as much weight reduction against factory castings (since 1974’s move to thin wall) as supposed just based on the ratio of iron weight to aluminum.

Bogie
 

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For starters, it's a 17' boat. using your solid roller that big will ause reversion, which is a motor killer. It will pull water from the risers and hydro lock.
It's a 17' boat so it should jump up on a plane in it's own length with a 383... unless the secondaries are opening too soon giving a bog... or valves are leaking... or both... the GM Hot Cam isn't a solid roller, it's a 218/228 hydraulic roller... it shouldn't hydro lock with one way flapper valves somewhere in exhaust system... I have similar cam in my boat...
 

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Hot cam is 218/228... similar to cam in my boat... no reversion with one way flapper valves in system...
Been working on boats all my life, and most don't even know if the flappers are still in the exhaust, and if they overheated once they aren't worth a sh^t. With factory short risers in a 17' boat, even with 110 the run is so close to the waterline you can get water. You are all correct if the flappers are in, but still any cam more than an rv style is about useless. remember, torque pushes. That boat engine was designed to start torque production like an rv, way down low and falling off earlier than hi performance automotive cams. boats very seldom see 5500 rpm, and most times run below 3800 so all that available in the higher rpm range is wasted.
 
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