Ignition Timing

Discussion in 'Troubleshooting & Diagnosis' started by Coadster32, Aug 7, 2017.

  1. Coadster32

    Coadster32 Veteran Member Lifetime Gold Member

    1,185
    41
    Oct 2, 2013
    Milford,CT
    Finally getting around to the the timing of the camaro. Specs: MSD distributor, coil, and 6AL box, 383 stroker, mild-medium cam (unknown specs), Edlebrock 1406 carb, Air gap intake, Procomp 64cc alum heads, dynatec headers, 2.5" exhaust, Turbo400 3000 stall, 3:90 gears. Street car only, runs ok. It was hooked up to ported vacuum, idle at 900, 8' initial, 1000rpm starts the curve, and 32'total all in at 2500 rpm. Vacuum advance puts me at 50' total. It would deisel on shutdown a good part of the time. I advanced to 12' initial, 36' total all in at 2500, and switched to manifold vacuum. The car seemed to run noticably better. The deiseiling has seem to gone by the wayside thus far as well. I'm thinking about stiffer springs, (don't have yet), to get the curve to start about 1200rpm, and be all in about 2800. Not sure if I should get an adjustable vacuum advance can as well, but not 100% certain if it's needed. Looking at 10hg at idle. I get the timing theories, just lacking practical experience. Will be moving on to dialing in the carb after I get the timing down. Open to opinions and ideas.
     
    Last edited: Aug 7, 2017
  2. larrylarry

    larrylarry Veteran Member

    1,292
    37
    Dec 22, 2011
    San Antonio Tx
    Vac advance, you don't need anymore than 10-12 hg an don't awant any advance from the vac can at idle.
    Stiffer springs will help.
    An adjustable vac can is good to have.
    IMO your carb is to small. I have an Eddy 750 (1407) on my 350. Just some advice, when asking for tune up info it'll go from one extreme to the other. The only way to get it perfect is on a rear tire dyno.
     
  3. Bandit723

    Bandit723 Veteran Member

    2,251
    262
    Oct 1, 2016
    Waupaca WI
    +1 on the dyno - As to the idle circuit adjustments a vac gauge will really help. shoot for the highest vacuum you can get and the most stable "steady" needle reading as well. an A/F meter goes a long ways as well.
     
  4. larrylarry

    larrylarry Veteran Member

    1,292
    37
    Dec 22, 2011
    San Antonio Tx
    If you can get it to where it doesn't ping, starts up fairly easy, doesn't start to misfire or lose power at WFO & the spark plugs look good then all is good, this is how my 78 is. I'm sure it could be tweaked a little bit but it's fast enough for me.
     
  5. Coadster32

    Coadster32 Veteran Member Lifetime Gold Member

    1,185
    41
    Oct 2, 2013
    Milford,CT
    It ran pretty well last night with the changes made. I didn't have any springs like said, but MSD recommends getting the curve to start just off idle anyway. I dialed in the idle cuircuts 1/8 turn at a time on each side, all while looking at my vacuum gage. 10hg is the best I could get, most likely because of the cam. Manifold vacuum does add timing at idle thru the vac can, and from what I have been reading, it should. I have a wideband hooked up, but figured I'd use that more for dialing in the carb. Currently it's in the 12.5 range at idle, then climbs to lean on the high end. I have some other jets and metering rods coming to help with that as well. With my cam, not certian if there will be inaccuracies in the readings of the A/F mixture. 12.5 seems rich at idle, but not certian what exactly my target numbers should be either. I figure that is all for another thread. Spark plugs look ok overall.
     
  6. joseph lamb

    joseph lamb Member

    42
    0
    Jan 1, 2017
    tampa florida
    Do the vacuum advance if you can , you will be happy , I did not for last 5 months and I do not know why I did , runs BETTER!!!!!!!!! street car
     
  7. Coadster32

    Coadster32 Veteran Member Lifetime Gold Member

    1,185
    41
    Oct 2, 2013
    Milford,CT
    Thanks for all the ideas thus far.
    I got back to it this past weekend. The springs in the distributor were the weakest ones they offer. They were coming in at 1000, and effecting idle smoothness. I went with stiffer springs, and it starts the curve at 1200rpm now. I got it at 14' initial, that puts me at 38 total. A little high from what most are suggesting, but I don't hear any detonation thru the range, starts pretty easy, and the run-on I was getting seems to have been disapated. In playing around with the jetting, I got 3/4-WOT to read 12.6%, and got the idle smoothed out a little better at 13.8%, with about 14hg vacuum. Seems pretty good. Currently am messing around with the mid-range. I'm between two metering rods, and two sets of step-up springs. One rod gives me 12.4 just off idle and mid range. The other 14.2-16.0. There is no in between size, so I'm going to polish the lean one down a tiny bit to help dial it in.
    In my opinion, if I can get the WOT to read 12.5 on a A/F gage up to my max rpm, the carb wouldn't be too small. If I was drag racing the car up to 8k, then I'd suspect my reading would be lean, telling me the carb would be too small. All things in perspective. Open to thoughts on that as well.
     

Share This Page