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Old 05-31-2008, 12:28 AM
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jetting carb

hi i am tuning my motor and its throwing white plugs, 70 jets in the front and 78's in the rear i was wondering should i try 72 and 80 or just bumping one of them up? its a 350 .030 flat tops 305 heads 1.95 intake 1.6 exhaust 54cc chamber,carb is proform 650 dp
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Old 05-31-2008, 01:49 PM
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What do you mean by "throwing white plugs"?

My first thought is that your compression must be pretty high with flat tops, and 54cc 305 heads. Are they aluminum heads or iron? Are you running pump gas or racing fuel?
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Old 05-31-2008, 04:44 PM
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well the plugs arent cream or black there white, on the tip when you take em out. cast iron heads 91 octane pump gas
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Old 05-31-2008, 05:10 PM
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you may want to check for a vacuum leak.
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Old 06-01-2008, 05:39 AM
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How does the car run?Are you checking the plugs by making a full throttle run and cutting the ignition,this is the correct way to do it to check the main metering circuit if it idles or cruises after the blast the color can be meaningless.One of the best ways to tune in for street use is go leaner until you get a lean surge then fatten up 2 numbers to remove the surge this will give good economy and performance.
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Old 06-01-2008, 11:22 AM
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yes that is after full throttle run it didnt surge cruising but plugs are white
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Old 06-01-2008, 07:45 PM
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White after a full throttle cut means add jet.try 4 numbers up and check again.Trial and error.
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Old 06-02-2008, 01:03 AM
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do the back jets have to be bigger than the front ones? cant they be the same>?
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Old 06-02-2008, 08:52 AM
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Depends if it has a rear power valve which is rare they will be the same or close, with no rear power valve a good rule of thumb is 8 numbers bigger in the rear, Is the carb jetted stock or have they been changed?Normally a box stock holley is somewhat rich to prevent engine meltdown.
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Old 06-02-2008, 11:19 AM
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it is jetted stock and it wasnt enough gas i have the front at 72 it likes that but the back is at 80's ans its to much on the topend
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Old 06-02-2008, 11:47 AM
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This may help. But if the plugs are white I would say run a colder plug.

The first plug is normal, the second plug is overheated, a few things to check before changing the heat range though. Read below:

"A clean, white insulator firing tip and/or excessive electrode erosion indicates this spark plug condition. k This is often caused by over advanced ignition, timing, poor engine cooling system efficiency (scale, stoppages, low level), a very lean air/fuel mixture, or a leaking intake manifold. When these conditions prevail, even a plug of the correct heat range will overheat."
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