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Runs better at 35 degrees advance?

Discussion in '40- & 55-Series Tech' started by JohnL, Aug 7, 2003.

  1. JohnL

    JohnL

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    I'm dialing in a new DUI distributor on my 74FJ40 "1.5F" and following the instructions to a "t." The engine is all warmed up, I've got it idling @ 690 with the vacuum hose off and blocked, and the "BB" on the flywheel lines up with the pointer when the adjustable timing light is set at 5 degrees of advance (for a total of 12 degrees BTDC.) So far, so good.

    For $hits and giggles, I started rotating the dist counterclockwise (advancing it) to see how the engine sounds. It keeps getting better and better, all the way up to 35 degrees of advance!

    Should I just stop fooling around and leave it at 12 degrees, plug the hoses back in and let er rip? Or is there something going on here? It seems to run smoother and smoother, faster and faster as I keep advancing it...at 12 degrees, it barely wants to stay running.

    Thanks for the help.
     
  2. Gumby

    Gumby Supamod Staff Member s-Moderator

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    At 35 degrees you will have a very hard time starting and you will have a lot of detonation. Your engine will not last long.
     
  3. JohnL

    JohnL

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    I would totally agree...in theory...that's why I'm wondering what I should do. I let it sit for 3 days, it has been pouring (v. humid!) and it started better than my new car. It seemed like the engine was off and running even before the 2nd cylinder fired!

    Is it normal for an engine to run strong when so far avanced at idle, and should I tune it by "ear" (gee, it sounds so much better when really far advanced), or just set it so it idles like crap and crank up the idle to 1000, or am I missing something?

    I agree, if I am really setting advance to 35 degrees, it wouldn't (shouldn't) run very long. I'm trying to figure out if I'm measuring something wrong, or what am I missing (fuel mixture? Idle? I'm measuring timing wrong?) At this point I have a feeling that I don't know what I don't know (except 35 degrees is suicidal!)

    Thanks
     
  4. theo

    theo

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    Unless you turn the idle down as you rotate the distributor, you're seeing a contribution from the centrifugal advance, which increases with RPM. So what you assume is 35 degrees static timing is probably less than that.

    You need to determine how much total advance that distributor gives, then set it according to how much total advance the engine can utilize. I know a 350 Chev can handle as much as 38 degrees or so total advance, and a 302 Ford maybe mid to low 30s. Not sure what is recommended for a Toyty 6.

    Here's some background reading for you:
    http://members.aol.com/DVAndrews/timing.htm
     
  5. Rice

    Rice SILVER Star

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    John,

    It sounds very much like your marks might be off. If the idle at 12 deg is so poor it truely sounds like the timing is retarded (a lot) which will not only give poor performance but also cause heating.

    Have you got a vacuum guage?? If so, hook it up. Timing is about right when you pull most vacuum at idle. After you find that spot advance it just a bit. It ain't perfect but it's very close and can tell you about your timing marks. As far as setting it "by ear" you'll know if there's detonation and you'll know it's set too high if it has a hard time starting when HOT.

    Let us know what you find out.
     
  6. SpaceGhost

    SpaceGhost

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    [quote author=Gumby link=board=1;threadid=4178;start=0#msg30945 date=1060307196]
    At 35 degrees you will have a very hard time starting and you will have a lot of detonation. Your engine will not last long.
    [/quote]

    Sup Todd?

    I caught that he was at 5 deg initial/static and then turned it up till he got 35 deg total advance. My DUI brings in 23 deg of advance, so I'm calculating he is at 12 deg initial, and it runs better. I don't think thats enough to cause starting difficulties, unless he has higher compression than I do. Mine is set at 14 deg initial, and 37ish total advance. It runs good this way, and starting is not an issue. I run the gear reduction (later) starter juiced by an optima, and charged with a huge mean green chevy alt. So his situation may result in different results.

    I also replaced the stock guages with mechanical, and my water temps stay at 180, which I used as an indicator that the timing isn't to far advanced. Also in talking with Clifford, DUI and Howell they all said the same thing, 35-40 degrees (like a small block) is ideal.

    On edit: As Rice said (is that Jack?), you must adjust the carb both idle speed and idle air as you increase the advance. I have always found the best running is whatever gets the highest vacuum at idle. You'll notice the vacuum drops as the rpms increase, so set the idle speed down as low as you are comfy with. 690 is way to high, regardless of the specs that are emmission influenced. 550 is a good setting for on road Cruisers in my experience.

    So, I'd run it like it is, lug the motor in a higher gear and if it doesn't ping/detonate leave it. If it does, ease it back it stops! If it bogs when you stab it, it's probably advanced to far, or so retarded it can't fire the mixture.
     
  7. Rice

    Rice SILVER Star

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    Not Jack ... Just Rice. I think Jack uses "Medusa" or something as a sign in.
     
  8. Chef

    Chef

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    Like Spaceghost said, if it's pinging, it's too much. Other than that, screw the specs, and run it where it works best. The vacuum guage is your friend, and so is your right foot when "tuning by ear." as others have indicated, as you make timing adjustments, you must reset idle speed and mix....
     
  9. JohnL

    JohnL

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    Workin on it...

    Fiancee in from out of town for a few days, so I'll come back and read this on Monday and tell you how it goes.

    FYI, my DUI weights are set up for 24 degrees of advance @ 3000 rpm.

    I'm running a normal compression head (forget the ratio), and the girl spends 1/2 time on road, 1/2 time on the trails. I run a later, but still externally-regulated alt, and a new gear-reduction starter. Plugs gapped at .053, according to DUI specs.

    If the suggestions don't work, I'll go get a vacuum gauge.

    For clarification, my comments were all based on idle, no accelerater involvement yet. According to my marks, I was at initial (idle) advance of 12 degrees. The flywheel was replaced ~2000 miles ago by a local Cruiser mechanic, who I have come to distrust, so I wouldn't be surprised if the wheel was installed without the marks lined up (if that's possible, I'v never had the flywheel off my self so I'm not sure if its "keyholed" or indexed.)

    Thanks all!
     
  10. Gumby

    Gumby Supamod Staff Member s-Moderator

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    [quote author=SpaceGhost link=board=1;threadid=4178;start=0#msg31050 date=1060356834]
    Sup Todd?

    I caught that he was at 5 deg initial/static and then turned it up till he got 35 deg total advance. My DUI brings in 23 deg of advance, so I'm calculating he is at 12 deg initial, and it runs better. I don't think thats enough to cause starting difficulties, unless he has higher compression than I do. Mine is set at 14 deg initial, and 37ish total advance. It runs good this way, and starting is not an issue. I run the gear reduction (later) starter juiced by an optima, and charged with a huge mean green chevy alt. So his situation may result in different results.
    [/quote]

    Hey, Mike
    My understanding is that he set it to 35 degrees at an idle with the vacuum disconnected. That would be 35 degrees base timing. Once it started advancing he would be at 70 degrees. That would be a bit much. :D

    I'm running 12 on my 80, myself. No pinging, lots of extra power. The factory setting of 3 is way too low for US fuel.

    If you are correct and he is at 35 total, then that's all good.
     
  11. willsta2000

    willsta2000

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    I would assume you haven't tried dirving it with it advanced that much. Sure it will seem to run like a raped ape in the driveway under no load, but try driving it before making any final adjustments. The shadetree mechanic's rule of thumb, as I recall it says advance it until it pings under a load, then back it off a couple degrees.

    Good Luck
    WILL