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im trying to time my motor...but timing keeps changing on its own!!!

Discussion in 'The Garage' started by 01maroonz71, Jan 29, 2007.

  1. 01maroonz71

    01maroonz71 1/2 ton status

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    well, here's whats going on...do i time my motor at idle??? or when should i time it...i think my timing is off big time, but when i go to rev my motor when im looking at it with the timing light, the timing retards quite a bit, like 6 or 8 degrees as i rev it. this is with the vacc. advance unplugged like the timing light tells me to do. is that suppost to happen???? this is new to me and am basically teaching myself...aside from all the tons of help i've been getting from ya'll.

    also, whats a good baseline to start from????

    and can i turn the dizzy while the truck is running, or will it shock the hell out of me???? i remember when i was younger i grabbed a dist. on my dads car and it got me good.
     
  2. wasted wages

    wasted wages 3/4 ton status

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    slop in the timing chain and gears.............
     
  3. Leper

    Leper 1/2 ton status

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    The base timing should be set with the vac advance unplugged.
    Need more info on your truck for more diagnostics.
     
  4. 01maroonz71

    01maroonz71 1/2 ton status

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    well, it's an 83 350 with a mild cam/holley double pumper/long tube headers/HEI dist/Turbo400 and it was dieseling every once and again, but now it's not. how would i know if the chain had slop in it??? the truck runs ok, but im only getting about 6MPG and everyone tells me the timing is the problem. oh yeah, and when it's cold...it takes like 5 or 6 minutes to get it idling ok.


    also...the vac advance is hooked to ported vac on my carb. if that matters.
     
  5. goldwing2000

    goldwing2000 Guest

    Are you sure it's retarding? The timing should move when you rev it but it should advance due to the mechanical advance inside the dist. If yours is actually retarding, then you may have issues.

    To check for slop in the timing chain, rotate the engine back and forth by hand with the dist cap off and see how much you can turn the crankshaft before the rotor begins to spin. If it rotates more than 1/8 of a turn or so, you should probably pull the cover and have a look at the chain.

    Base timing changed a lot during the 70s and 80s due to various attempts at emission controls but it should be *approximately* 6° BTDC @ 700rpm with the vac advance disconnected and plugged.

    Also check to make sure your harmonic balancer isn't crapped out. If the rubber portion has rotted, then the outer part will spin on the inner part and your timing marks will be meaningless.

    6mpg is definitely a problem.
     
  6. blazinzuk

    blazinzuk Buzzbox voodoo Premium Member GMOTM Winner

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    pull your cap off and make sure your advance is working. I would think that if it retards when you rev it that might be the problem.
     
  7. ryoken

    ryoken Puppy Fabricator Premium Member GMOTM Winner

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    I have a sneaky suspicion the timing is advancing and he's confused...
     
  8. 01maroonz71

    01maroonz71 1/2 ton status

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    right you were...it was advancing...but i set the base timing at actually 10degrees BTDC and idling in gear at 500RPM...i got that off autozones site.

    it was at about 7degrees BTDC and now it seems to run alot better...way more "peppy" when i hit the gas. maybe if i bump it two more it would help more...or do i have this all wrong????

    would that cause my motor to get bad mileage??? or maybe getting the carb rebuilt is in order.

    thanks for your help guys....

    hey Goldwing...how in the hell did you get the degree symbol...i can't find it anywhere on my damn keyboard. you must know magic.
     
  9. ryoken

    ryoken Puppy Fabricator Premium Member GMOTM Winner

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    10 is a very norm base on sb chevys... you might wanna check your total advance, much more important imo... sb chevys generally like 32 to 35 degrees after 3000 rpm's... more if it's got alot of cam...
     
  10. 01maroonz71

    01maroonz71 1/2 ton status

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    don't kill me, but how would i check total advance if it goes off the timing tab??? and would i just have soembody rev the motor to like 3k while i check???

    maybe that's murdering my mileage....and also, is that adjustable...

    thanks again guys!!!
     
  11. ryan22re

    ryan22re 1/2 ton status

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    You'd need an adjustable timing light. And somebody to watch the tach and/or work the throttle.
     
  12. 01maroonz71

    01maroonz71 1/2 ton status

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    i see..i believe my timing light is adjustble...so i adjust it until it matches my BTDC timing and them whatever the gun is set at...ie..32degrees..that's what it is???? how would i adjust the advance at that point???? thanks!
     
  13. ryoken

    ryoken Puppy Fabricator Premium Member GMOTM Winner

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    Sheesh, I must have a hella rep around here... :doah: :wink1:

    You'll need a timing light with an adjustable advance knob... or a timing tape...

    advance curves (how quickly the advance comes in) can be changed with different springs...

    How much mechanical advance comes in can be changed too, but that is a little more involved...

    adjustable vacuum advances are available too...

    I usually check total advance and see what it backs off to at idle...
     
  14. ryan22re

    ryan22re 1/2 ton status

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    If you have 30 degrees total timing, you should be able to set the gun to 30 and the marks line up at zero. That's the only way I can think of it. adjust the light to get the timing tab to read zero. T
     
  15. ryoken

    ryoken Puppy Fabricator Premium Member GMOTM Winner

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    Thats correct... set the knob to 32, spin up the motor over 3 g's, mark should be at tdc...
     
  16. 01maroonz71

    01maroonz71 1/2 ton status

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  17. goldwing2000

    goldwing2000 Guest

    Hold down the ALT key and then hit 0176 on your number pad. It pulls it right from base unicode.

    Also, you can open MS Character Map and then copy and paste all sorts of symbols and special characters from unicode.
     
  18. ryoken

    ryoken Puppy Fabricator Premium Member GMOTM Winner

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    sure.. low base timing and not adjusted properly vac advance can certainly hurt mileage... I wouldn't expect more than 10, 12... should be able to adjust that with a small allen iirc.. maybe check mallory's site for some pdf's...

    Hope that Mallory works out good for ya... I ran a unilite yrs ago, didn't particularly care for it.. ended up swapping in an MSD...
     
  19. goldwing2000

    goldwing2000 Guest

    Be sure to check your balancer for problems, too. Pull out the number 1 plug, stick a skinny screwdriver in the hole and rotate the engine by hand. When the piston is at TDC, the timing mark should be at 0. If it's off, start looking for a bad balancer.
     
  20. 76zimmer

    76zimmer Flyin Rat Premium Member GMOTM Winner

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    It would be kinda hard to get true TDC (piston)with a head on wouldn't it?
     

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