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Carbon build up after very few miles?

 
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Rbace123
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PostPosted: Thu Jun 03, 2010 7:39 pm    Post subject: Carbon build up after very few miles? Reply with quote

I noticed when I changed my head gaskets there is more carbon on the pistons and heads then I thought looked normal. It was a build up of about 1/16 ". Not just discolored. Motor only has about 2000 miles. Is this a condition of carb adjustment or what is the fix? Motor is 383 stroker, AFR heads Comp cams hydraulic roller, holley 750 dp carb. Should I let the local performance shop dyno tune it or some other fix.
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clay
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1972 Chevrolet Nova

PostPosted: Thu Jun 03, 2010 11:29 pm    Post subject: Reply with quote

Definately sounds unusual to me. When I burned a piston at about the same mileage as you, the other pistons were discolored but pretty much clean. They had the thinest layer of carbon, but most of the top was just a dark brown with very little if any buildup. I have a few ideas. To me, heat is what keeps the chamber clean. Things that can cool off the burn and let carbon buildup would be the normal excessively rich mixture, too much stop and go traffic without proper use of the throttle Very Happy (I'm assuming you didn't build a 383 / AFR setup to put around), too much piston to head clearance at TDC, tool cool or even no thermostat. If you aren't burning oil then running it hotter and more high rpm higher load operation should keep the chambers and pistons cleaner. This is just my first round of guesses. Post some pics of the buildup and the plugs unless you have already put it back together. Clay
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Rbace123
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PostPosted: Fri Jun 04, 2010 1:15 am    Post subject: Reply with quote

Yeah it is already back together and I didn't take any pictures. It is not real bad but there is a definite layer in some places. THe plugs looked really clean except the one where the head gasket was blew. I was getting coolant in # 3 cylinder. I am leaning toward the burning too rich. I know it is rich at idle not sure if that would make too much difference.
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jeep_406
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Location: Tewksbury, Mass 01876
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1972 Chevrolet Nova

PostPosted: Fri Jun 04, 2010 6:37 pm    Post subject: Reply with quote

Just some thoughts in no particular order:

Does the vacuum at idle drop below the power valve in the carb Question
Did you use low tension rings Question
Was the buildup across the entire piston Question
Was it clean on the outside of the piston top near the cylinder wall Question
Does it use any oil Question
How much cam are you running Question
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Rbace123
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PostPosted: Fri Jun 04, 2010 8:09 pm    Post subject: Reply with quote

Not sure about the vacuum at idle it is one of those things I need to check. It is the stock power valve in a holley 750 DP.

The rings are plasma moly rings that came with the Mahle forged pistons.

Build up was not across entire piston but can not really remember exact patern now.

Does not use any oil that I can tell. No smoke now after fixing head gasket.

Cam is Comp Cams Hydraulic Roller Cam #12-433-8

http://www.compcams.com/Cam_Specs/CamDetails.aspx?csid=161&sb=2
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clay
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1972 Chevrolet Nova

PostPosted: Fri Jun 04, 2010 8:26 pm    Post subject: Reply with quote

Most likely the power valve is a 6.5. It shouldn't be giving you any problems with the cam you have listed. I would guess you are idling around 10 " or maybe a little more depending on your distributor setup. It won't actually affect your idle mixture if it is open at idle though. It adds jet area to the main well that is also supplied by the main jets. If for some reason your engine couldn't make enough vacuum once you started opening the throttle, then it would show up as a possible rich cruise and definately start showing up by 1/4 throttle as being rich. Power valve and idle problems are when it has a leak around the gasket that seals it to the metering plate or if the diaphram is ruptured. You could possibly have a gasket issue, but you don't have a diaphram issue or it would be barely running and reeeaaalllllyyyy rich. I forgot to bring my piston home from work so I could take a picture for you to compare and I've already cleaned the others up. Hopefully you don't have a problem at all. Let us know how it goes. Clay
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clay
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1972 Chevrolet Nova

PostPosted: Fri Jun 04, 2010 8:33 pm    Post subject: Reply with quote

Found a pic in my postmortum post.

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af2
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1933 Willys Coupe

PostPosted: Fri Jun 04, 2010 8:58 pm    Post subject: Reply with quote

Rbace123 wrote:


Build up was not across entire piston but can not really remember exact patern now.

Does not use any oil that I can tell. No smoke now after fixing head gasket.


http://www.compcams.com/Cam_Specs/CamDetails.aspx?csid=161&sb=2

HMMMMMM Thinking!
1/16" carbon where.

To faige of question to go from. Clay is spot on but still need more info.
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10sec.et
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1969 Oldsmobile Cutlass

PostPosted: Fri Jun 04, 2010 11:32 pm    Post subject: Reply with quote

10 years on this one....




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af2 wrote:
It seems we can look at our magical Balls and come up with a fix?

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af2
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1933 Willys Coupe

PostPosted: Sat Jun 05, 2010 2:27 am    Post subject: Reply with quote

10sec.et wrote:
10 years on this one....





That is why we have 5 bolts per cylinder! No water to clean the pistons. Laughing Poke

Just messin with Texas. Shocked
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