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Old 09-22-2010, 08:01 PM   #1
Join Date: Aug 2010
Location: Bear creek, NC
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Default compression on a 1995 4.3lx vortec motor

what are acceptable compression numbers for my 1995 4.3 vortec 4 barrel carb motor?
Im getting 150 pounds accross the board +/_ a lb or two but for the most part they were no more then 2 lbs difference between the cylinders and 150 lbs is this ok? or acceptable? Im still having issues with it starting after new fuel system new ignition system. Im getting spark the motor is in time. rebuilt carb is giving fuel. i just dont get it. im at a loss of why it wont start

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Old 09-22-2010, 08:28 PM   #2

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150psi is right up like one of 2 things...
how is the choke set...???with the engine cold...pump the throttle once...look at the choke should slam shut...
then pump the throttle in neutral 3 times...full strokes...this primes the throat of the carb and gets gas into the cylinders...leave throttle about 1/4 fwd in neutral...
hit the starter....should fire right up...
2nd thing to check is for a vacuum leak at the base of the carb...using a squirt bottle filled with soapy water.....while the engine is idling...shoot a stream of water at the base of the will change in pitch and smooth out for a few seconds....

no vacuum leak...


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Old 09-22-2010, 10:10 PM   #3
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I think im still back at a spark issue...... I have a brand new dist cap and rotor new plugs new plug wires, put a new coil on it about 2 months ago. compression is at 150 at all cylinders +/- one or two psi. Rebuilt carb as of last month new fuel filters new fuel pump new check valve, fuel tank vent is not clogged new fuel lines, checked fuel pickup its clean. getting plenty of fuel to carb. still wont start!!!!! I dont see a spark when i ground the spark plug to the block but when i stick a flat head screwdriver in the spark plug wire and hold it a few cm from a ground i see a small spark but it comes and goes its not consistant with the engine cranking. why am i getting week spark? could my coil be bad already even though its only 2 months old? I have spent hundreds of dollars trying to fix the issue and nothing is helping any other suggestions?
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Old 09-23-2010, 03:48 PM   #4

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Check all the grounds to the block - make certain they are clean and tight.
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Old 09-24-2010, 12:36 AM   #5
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what is the two black wires go to? they were disconnected since I have owned the boat. and boat ran fine when I first got it. it is between the dist and the circuit breaker
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