Questions for the ignition timing gurus: from retard to advance

Discussion in '40- & 55-Series Tech' started by DSRTRDR, May 15, 2006.

  1. DSRTRDR

    DSRTRDR I can mangle anything ... SILVER Star

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    Hi,

    I would like to learn what the implications are for emissions if I go from retard timing to advance? When the cruiser was last tested and passed, hydrocarbons on idle were just below the limit (everything else real low :D). I need to get the cruiser tested again in the summer :frown: and was wondering whether switching to advance would make it harder to pass emissions?

    Also, Mark drilled the carb for advance vacuum (currently closed off) but where do I hook it up to the distributor? and do I then simply clamp off the vacuum lines I am currently using? Sorry if this question is stupid, but hours of looking at SOR diagrams have yet to enlighten me :rolleyes:

    I'd very much appreciate your help! Thanks in advance :)
     
  2. IDave

    IDave

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    Aren't you emissions exempt with a 72 where you are, C?

    Anyway, you need a vacuum advance distributor to go that route. Then you hook up to the vacuum advance port on the carb.

    Dunno about emissions. I've not had a car checked in 20 years....they don't do that here.
     
  3. rgentry

    rgentry

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    Since we are waiting for the gurus ...... As far as I know the advance distributor will not change the way your engine runs at idle. Both the vacuum and mechanical advance come on as the engine comes off of idle. The throttle has to be cracked open for the vacuum advance port to see vacuum, and the engine RPMs have to go above 1000 r.p.m. or so before the mechanical advance begins. Therefore, I see no change in emissions (at idle).
     
  4. DSRTRDR

    DSRTRDR I can mangle anything ... SILVER Star

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    AZ emissions tests ALL vehicles in Maricopa country (Phoenix has a bad air problem) :frown: they are stricter in their testing requirements for older vehicles than California in that regard :rolleyes: Nebraska couldn't care less, but there is no wheeling here :frown:
     
  5. Pin_Head

    Pin_Head

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    In general, HC comes from misfiring, but it can also come from a burned exhaust valve. If it is only a problem at idle, the most likely cause is due to a lean condition at idle (too low to ignite by spark) because of a vacuum leak.
     
  6. DSRTRDR

    DSRTRDR I can mangle anything ... SILVER Star

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    It did pass emissions; I am now looking into the possibility of going to advance timing, but need to know whether I need to anticipate an effect on emissions. Any help wwould be appreciated.
     
  7. Pin_Head

    Pin_Head

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    The major effect of fiddling with timing is to alter combustion temperatures, which effect NOx levels. The NOx emission standards for pre 3-way catalyst vehicles are pretty generous. If the timing is so far off as to promote incomplete combustion or misfiring then it would also alter CO and HC levels. In the people's republic of CA, they check the timing and ding you if you are a few degrees off.
     
  8. IDave

    IDave

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    Is she likely to have those problems if she switches to an advance distributor, Charlie?
     
  9. Pin_Head

    Pin_Head

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    I don't really know, but I doubt it. All I know is that vacuum retard distributors and EGR valves came into use in the mid 70s as a means of lowering NOx. Just take your chances and see what happens.
     
  10. Poser

    Poser Oh...Durka Durka Durka. s-Moderator Supporting Vendor

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    What is there to gain by going this route....seriously?



    If it works well, why F with it?
     
  11. IDave

    IDave

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    That's a good question. I suppose Mark tapped it for advance for a reason?
     
  12. DSRTRDR

    DSRTRDR I can mangle anything ... SILVER Star

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    he mentioned it would be advantageous, but I have forgotten why :doh: :frown:

    guess I have to contact him directly since this thread doen't seem to get the right traction ;p

    I thought the general information would have been of wider interest, but maybe not.......
     
  13. IDave

    IDave

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    I just spoke to Mark and asked him to weigh in here. Hopefully he'll get a chance. He referred me to his FAQ, and here are the pertinent paragraphs, but the "why" still evades me.

    b. MODIFIED AISAN CARBS. I have been ‘tinkering’ with the Aisan carb almost as long as I have been rebuilding them, which is a very long time. As far as I am concerned, the Aisan is one of the most sophisicated carbs ever designed. IMO, Aisan, as a semi-autonomous company, was more or less forced to severely restrict the operation of a very capable carburetor in order to meet Toyota’s new car emissions standards.
    It all started with a tinkerer’s natural curiousity. Looking at a disassembled carb I asked myself, why would the Japanese, who greatly embrace functionality, design a carb with superflous ribs and ports that don’t seem to go anywhere. So I started experimenting, putting things together, in different combinations.
    With the F engine carbs from 70-74, the first thing was to calculate the right location to port them for vacuum advance, effectively making them non-US carbs. With the 2F, the focus was on improving the operation of the secondary circuit. I haven’t stopped tinkering yet, as new ideas come along, I still break out the micrometer, the calculator, and the drills. Lately, I have made a few modifications to my SD-40 1bbl carb that I am pleased with, and have a couple more to try.
    It should also be noted that so far, none of the modifications I have made or offered has caused a customer’s vehicle to fail an emissions test. A few have noticed a decrease in mileage, but this is only because they cannot resist using all the extra power available after the carb work!
     
  14. DSRTRDR

    DSRTRDR I can mangle anything ... SILVER Star

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    I guess he is saying there is a power gain, that would be a good reason. :grinpimp:
     
  15. IDave

    IDave

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    I think so, too. But I'm not sure if that's from the switch to advance or some of the other tinkering he does. It would be nice to be able to say why (but perhaps it's proprietary info...) :D
     
  16. Poser

    Poser Oh...Durka Durka Durka. s-Moderator Supporting Vendor

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    That piece was specifically about modifying carburetors and stated nothing about vacuum advance vs. vacuum retard distributors, the effects on emissions when changing from a retard unit to an advance unit, or the performance that one would expect to gain by installing a vacuum advance distributor in a truck originally set up with a mechanical advance and vacuum retard distributor.
     
  17. DSRTRDR

    DSRTRDR I can mangle anything ... SILVER Star

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    and all of these points I need some enlightenment on :rolleyes:

    More specific question, do I get this correctly, when I switch to the advance vacuum port on the carb, I will also have to change the connection at the distributor? (or install a different distributor - I am still trying to figure out what I actually have - the dizzy looks like it came with the '76-'78 2F that's in the truck). My dizzy currently has a clamped off port that I suspect I would use with vaccum advance, but I what I don't know is whether I have to disconnect the current line from dizzy to carb. And I don't want to just try something before knowing of potential ramifications for emissions.
     
  18. beaufort-fj60

    beaufort-fj60

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    start the motor and while it's idling, take the vac hose from the distributor and place it in your mouth. suck on it and see what happens, something will happen. the engine will speed up or slow down.
     
  19. IDave

    IDave

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    You definitely need a different distributor: the nonUSA advance. You don't want to mix an advance carb port with a retard dizzy, or vice versa; things go the wrong way at the wrong time.

    Also, on an advance dizzy the vacuum diaphragm points to the front. Retard dizzy diaphragm points to the back.
     
    Last edited: May 16, 2006
  20. Poser

    Poser Oh...Durka Durka Durka. s-Moderator Supporting Vendor

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