RUN-ON AND HESITATION PROBLEM..DESCRIPTION KIND OF LONG.

I BOUGHT A 305 SBC FOR MY TRUCK. MOTOR WAS STILL IN A FRIENDS TRUCK BEFORE I HAD BOUGHT IT SO I GOT TO CHECK IT OUT PRETTY GOOD. NO SMOKE AND NO KNOCK. RAN REAL GOOD. PUT IT IN MY TRUCK. I TIMED IT TO 8 DEGREES BTDC. STARTS AND IDLES GREAT BUT WHEN I TAKE OF IT HESITATES. IF I GIVE IT LITTLE MORE GAS IT TAKES OFF A LITTLE STRONG. IF I HOLD DOWN BRAKE AND THROTTLE IT HIGH IT SOUNDS GOOD AND MAKES THE TIRES SPIN ON ASPHALT, BUT POOR TAKE OFF IF I JUST TRY TO ACCEL SLOWLY. AND SOMETIMES WHEN I TURN IT OFF THE ENGINE WILL SHAKE AND ACT LIKE IT WANTS TO START BACK UP AND MAKE A WEIRD SOUND COMING FROM THE CARB AND THEN STOP. SO I TRIED 10 DEGREES BTDC. SAME PROBLEM.IT SUPPOSE TO HAVE AN RV CAM IN IT. IS 8 DEGREES BTDC ACCURATE? PLUS VACUUM IS LOW. VAC GAUGE READS LIKE 12. SHOULDN'T IT BE HIGHER? I CANT GET IT TO GET ANY HIGHER UNLESS I TIME IT LIKE 16 BTDC THEN I GET MORE FREQUENT RUN ON OR DEISLING..CANT STAND IT..NEED HELP!!  

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Is the engine over heating.  
Professional hi-performance engine builder

Horsepower sells Engines and torque wins races.

The motor's dieseling (when it wants to keep running with key off) because the timing is out of adjustment.

You need to retime the motor. First though, does your friend have the part number for the cam he isntalled? Then you can look up timing specs.

If you don't have a part number, reset the advance to zero, see how the motor runs, and advance the distirbutor a couple of degrees from there and see what happens.

Also, if this is an early HEI distributor, the springs and coutner weights oculd be wrong/bad and need changing.  

i would also bring the harmonic balancer up to the 0 mark..   then back it off with a socket on a breaker bar  till you feel the slack out of the chain....   go back and forth a few times...    if you have more than 1/2 inch of movement of the timing mark on the balancer... you may have a really loose timing chain...   there will almost always be some slack... but when it gets over 6 degrees ... it might be time to change the chain...  and don't get too excited if you find close to that..  as only half of the slack is actually retarding the cam...    


another thing...      hesitation when first opening the throttle...   i would with the motor slightly warm...  pull the air cleaner... with the engine off.. move the throttle and see if the pump shot is instant...   if it is late.. there are several things it could be...     improper adjustment of the accelerator pump lever.. hard to do on a q jet.. but possible...

it could also be the pump seal is worn....   the check valves in the pump circuit could also be leaking...    clogged pump shooter nozzles...   loose or distorted top on the q jet.  don't just tighten  the hold down screws...   tighten slightly all the screws that hold the top to the carb.. including the 2 inside the air horn..


as for running on... when you try to shut it off.... i would try to reset the idle speed... slow it down...

adjusting the idle mixture has to be done at the proper idle speed...  if you adjust it at a higher idle speed... when you slow it down.. it will be too rich..  all this extra speed at idle wastes gas.. the motors are just struggling to overpower the converter and the brakes..

with the low vacuum .... and the running on..     i would also check the secondary throttle blades for leaks...   sometimes they get pushed off center when the carb is set down....   the carb has to come off to reset them...  DO not loosen the throttle blade screws more than a quarter turn..  they are mashed.. and will break off...

the last thing... check for vacuum leaks....   pinch off various vacuum hoses.. like the power booster hose...  and what ever else is there... if the engine changes speed... you may have found one of the problems...

i guess i will have to write a post about idle mixture adjustments..  

maybe this week....  

wayne712... in hollywood ca...