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327 running rough

I love my Chevy Chevette!
Posts: 3
Joined: 12/12
Posted: 12/17/12 06:06 PM

Have a 327 bored 30 over, 10:5 flat top pistons, avenger 770 carb, brodix alum. intake, roller cam, 2.02 valves on the double hump heads, alum 1.5/1.6 rocker arm, engle roller cam. and HEI distr.  Never put on dyno but engine runs weak.  Current problem is fuel on the spark plugs very rich black smoke out of exhaust.  Is my carb to big 2nd set of plugs used or do i need different distr. system.  With was a father son project and father passed away. (he was the brains of the garage).  Any help would be great.  Engine sits in a 1963 SS Impala, all stock.  

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My first time was in a Chevy
Posts: 218
Joined: 04/12
Posted: 12/17/12 11:03 PM

first... welcome to the forums...

wow.. a 63 SS impala 327.. cool... have you priced them lately...

be careful where you drive and park it at..

out here in los angeles.. those are dangerous to drive.. people will car jack you for them
a friend of mine lost his 64... it was on a 2 post hoist... with cars under it.. locked shop doors.. cars blocking the doors... cars blocking the gates into the shop parking lot..  they moved them all to steal the nicely restored 64 .. not a show car.. just nicely restored..  

is your carb too big..   probably not.. lets get it to idle and to run at lower speeds without flooding / fouling the spark plugs first...  too big only counts really at above cruise speeds..

why don't you start with a few videos from holley performance on various parts of their carbs..

here is the full section on holley carbs...

watch all the videos on carbs... watch them again..

come back and post what you found with your carb..

i am going to say that after watching these videos you are going to have one or more of these issues..

incorrect float levels..

leaking needle and seat...

too much fuel pressure forcing the needle and seat open.

dirt or teflon tape in the needle and seat..

rust from the fuel lines that goes right through the fuel filters holding the needle and seat open.

blown out power valve...

totally incorrect idle mixture screw setting..

blocked idle air bleeds...

blocked high speed air bleeds..

and a rare but still happens..  usually not on holleys..   fuel lines attached to the PCV port..
i think in 30 years.. i have found 3 of them hooked up that way when i was called over to help get a car started..  oh.. all 3 also had the PCV hose hooked to the fuel inlet on the AFB/AVS carbs..  

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I love my Chevy Chevette!
Posts: 3
Joined: 12/12
Posted: 12/18/12 03:55 PM

Thanks will check them out, Thanks she is my baby but i would love to trade for a 55 chevy.  

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Big Block power for the win
Posts: 940
Joined: 03/11
Posted: 12/18/12 07:46 PM

Kbrock: Welcome to Super Chevy

First I'm sorry about your dad. We all face that same thing at some time in our lives.

1.Did your dad have the engine running before he passed away?

2.Is that the same gas in it before your Dad passed away? If it's the same gas it is stale, or no good. Your going to have to dump it all. Drain the complete fuel system take the carb off and drain it, blow all the lines out. Install a new fuel filter. Install fresh gas and this time put some "Sta-Bil" in the gas. Just follow the directions on how much to put in each gallon. I would go that route first if it is the old gas. Grin  Cool

3.I don't think your carb is too big.

4.You don't need a different Distributor.

5.Set the gap on your spark plugs to.032-.035

6.I have a couple questions.
A.Is the cam your using an Hydraulic Roller, or a Mechical Roller cam.
B.Whatever the cam is it set correctly? Is it timed correctly at the crank.
C.If you have the specs for the cam send them to us.

Merry Christmas

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I love my Chevy Chevette!
Posts: 3
Joined: 12/12
Posted: 12/25/12 05:04 PM

Thank you for the nice words of my father, this engine is a new engine since his passing.  I have removed the gas tank and installed a new one since.  The can is a hydraulic Roller, i have to check and see the specs on the cam.  Yes i do have Sta-Bil in the tank.  

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Big Block power for the win
Posts: 940
Joined: 03/11
Posted: 12/25/12 09:03 PM

Your welcome Kbrock.

Give us as much information as you can. It can be a miriad of little things, just adding up.

You may also have some valves that aren't adjusted quite right. The intake valves may be hanging open.

Is it popping back through the carb?

Let us know.


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V-6 Camaros rule!
Posts: 39
Joined: 05/10
Posted: 12/31/12 01:14 AM

.. The carb. is biggish for that engine, but should run acceptably well...

.. I assume you've already checked for proper fuel levels in the float bowls...

.. The stock jets in a carb. that big may be too big... primaries prolly should be in #66 - #70 range, secondaries in #74 - #78 range... or same as primaries if your carb. has a secondary power valve in rear of carb. in addition to the primary power valve...

.. Most likely the power valve(s) are for too high a vacuum for your camshaft size and staying open all the time, not just when you ask for power with your foot... (a vacuum leak at gasket under carb. can also do that)...

.. Sounds like Dad was a great guy who would have a vacuum gauge or tester... you need to discover your idle and 70 MPH cruising vacuum levels and make sure your power valve(s) are rated for 2 or 3 numbers lower than that so they stay closed until needed and aren't flooding the engine with gas all the time...
i.e., if you have about 10 inches of idle vacuum, need about a 7 or 8 power valve(s), etc... the number is stamped into the side of your power valve(s)... most carb.s come with about a 10.5... which wouldn't work for our example...

.. The powervalve(s) and jets are in the block of metal between the float bowls and main body of the carb...

.. Is your car manual or automatic tranny?  

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