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Old 12-16-2012, 08:22 AM
cdminter59 cdminter59 is offline
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Blowback through carb

Post all the information you can about your motor. Brand of crankshaft, rods, pistons, head gasket compressed thickness or part number, brand and type heads, , brand of spark wires, type of spark plugs AC R45, part number of camshaft and type, hydraulic or solid tappet or Roller cam. Who built the motor? Who setup heads. Have you checked for vacuum leaks? Spray starting fluid all around intake flange and carburetor base at gasket. If idle goes up you have a leaking gasket. Tools you need are a vacuum gauge and timing light with advance. (has a knob on back end) Check spark plug wires with multimeter to see if you have continuity. What kind of car or truck (year and make) is the motor in? Read this article on HEI distributors and timing. Use the vacuum gauge to set idle mixture screws. Make sure your fuel pump pressure to carburetor is about 5-5.5 psi. How or what adjustments did you make to the jets on the QFT 680? Has the engine back fired thru the carburetor if so you may need to replace power valve. Get a vacuum reading at idle. If the reading is say 10 divide by 2 = 5. Use a 4.5 power valve. Here is the instructions for your carburetor.

Last edited by cdminter59; 12-16-2012 at 08:40 AM. Reason: spelling correction
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