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Timing 101a


Shelby
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there seems to be some  arguement about  checking the base timeing with or with out the vacum advance  hook'd up

the normal operation of the vacum advance system is to not have enought vacum at  hot idle to advance the  timeing, thats why the manual  says  nothing about  unhooking it, BUT  all things are not always as they should be , so to asure the  vacum advance is not holding the timeing any , it  takes no time at all to  unhook the hose and see if it is, and sence you already have the timeing light on  it  why not set the base timeing   while you  know  for a fact the  timeing is at base

then it's a simple matter to  recheck it after putting the hose back on

while  we're at  seting the base timeing it's a good time to check a few other things  such as the mechanical advance system, easy  just  rev the engine  while watching the  timeing mark , with  a  moderate rev of  2000 to 2500 the timmeing mark should  move advance'd about  10  aditional degrees from base , and  with a rev to 4k or so it should  be aprox 33-35 btdc, this is with out the vacum advance hook'd up, if  every thing is in the ball park, connect the  vac hose back up and  lightly rev the engine the advance now  should be much  greater then it was with out the  vacum hose on , the  vac  adv port  will rearly  see full  manifold vacum  but 10to 12  inches of  vacum should advance the timeing  10 to 12 degrees, this is adj by the  way.

now in less then 5 minutes you have done a  bunch of things, not just  set the base timeing and call'd it  done, you've check 'd out the dist advance system, the vacum advance system and the  base timeing plus check'd the throddle  for being close'd in the idle possition

if you  have a enought vacum at idle to move the timeing  you'l need to redo the  ISC, TPS, and MPS adj , and check the cable  for proper slack ,and the  hoses  for any  leaks, includeing the inj houseing  

 

now there is much more to the dist and it's advance systems  but this is just a guick check  you should do when seting the timeing , not just  say it's at 10 btdc and call it a day , and it only takes a couple more minutes

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  • 7 months later...

Good call Shelby.

  Thanks, I need to set the timing again after this thread. I set it 10 BTDC and called it the day.

 

                                                                         jb

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  • 3 months later...
  • 11 months later...

what would cause a high vacuum at idle?  because my timing gets pretty dang advanced when i re-hook up the vacuum line. we set my base at 10BTDC with the line NOT hooked up.

 

does the vac. advance not affect the engine when under boost?

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  • 2 weeks later...
  • 3 years later...
what would cause a high vacuum at idle?  because my timing gets pretty dang advanced when i re-hook up the vacuum line. we set my base at 10BTDC with the line NOT hooked up.

 

does the vac. advance not affect the engine when under boost?

 

 

several reasons for this,, the most common is useing the wrong vacuum port

th1st of the 3 ina row ports on theTBI system is a port'd vacuum , meaning it does not see any vac signal ntill thethroddle plate is open'd some,, then it drops off after a certain distance of travel example 1/2 way to wot

 

for non oem ntake systems you donot want to use a full vacuum signal port,, unless you have a throddle body with a port'd vac signal port,, you need to forget about useing the vacuum advance funtion of the dist all togather,,but retain the retard under boost funtion by useing a boost only signal port ahead of the throddle plate

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