Detonation - vacuum adjustment

Electrical & Ignition

  1. HWYCRZR

    HWYCRZR Senior Member FCBO Gold Member

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    Ross you may already know this process, but in case it is unclear or we are informing others, here goes. One adjustment at a time. Vacuum advance setting:
    Check your specs from the FSM. It is in the electrical section right before the schematics. (You probably already know this). I used a small hand pump vacuum actuator. First step, make sure that at idle you have less than 8 or so inches of vacuum going to the canister. If you have more than 8 your butterflies may not be seated (maybe due to too high of idle setting not allowing the butterflies to close all the way.) causing vacuum advance to open early. If ok, plug port from carburetor and hook vacuum hand pump to vacuum advance canister port. Hook up timing light and start engine. Start adding vacuum with your hand pump, watching your timing mark, when it starts to move record that spec and compare to the FSM spec. If it is opening sooner than spec you may get detonation on acceleration. If it opens later than spec you may feel a hesitation on acceleration. As said up above. Clockwise opens it earlier, counter clockwise opens it later. Mine used a 3/32” Allen wrench.
    Mine was opening at about 14” which was advancing later than I liked, causing a hesitation (I am running a 2bbl so may differ from your 4 bbl specs.). I dialed it back to around 10” per spec. Do a half turn at a time. This really helped my hesitation issues when stepping on the throttle, but not opening to early to cause detonation.
    Happy tuning.
     
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  2. Ross Wooldridge

    Ross Wooldridge Senior Member FCBO Gold Member

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    Great instructions, and yes, that was kind of my plan, although I hadn't though about it yet in so detailed a way.

    Thanks!
     
  3. mr. fix it

    mr. fix it Old Man with a Hat

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    Watching thread:)
     
  4. Ross Wooldridge

    Ross Wooldridge Senior Member FCBO Gold Member

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    So - I finally got a chance to get the old 3/32nd Allen key out and play with the vacuum advance can on my car. 1/2 a turn counter clockwise made a big improvement in reducing the part throttle detonation. Another 1/4 turn made a little more, but not as dramatic an improvement as the first 1/2 turn.

    Now I would call the detonation "trace" as opposed to obvious. I suspect now that further improvement will be found in areas like the carb and the actual curve/weights/springs in the distributor.

    Ultimately, the drivability is MUCH improved already.
     
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  5. mr. fix it

    mr. fix it Old Man with a Hat

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    Good news Ross :thumbsup:

    How's the timing chain doing?
     
  6. Ross Wooldridge

    Ross Wooldridge Senior Member FCBO Gold Member

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    Still there behind the cover ASAIK...
     
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  7. Ross Wooldridge

    Ross Wooldridge Senior Member FCBO Gold Member

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    So - it was suggested that the remaining "trace detonation" (which seems to appear more as the engine gets to full operating temp) may be due to carbon deposits and they suggested I use a combustion chamber cleaner.

    Here in Canada I'm finding it hard to find any additives that make that claim directly.

    Is there a product anyone swears by, and how is it used? Spray in? Add to tank?

    Also, what's the best octane booster?
     
  8. Ripinator

    Ripinator Senior Member

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    Ross: I suppose you could try a couple of bottles of SeaFoam, and see what that does. . . As I have mentioned in the past, I run one ounce of Marine 2-cycle oil (with TC-W3) per five gallons of gas in all my cars. Over time, this should gradually clean and keep clean your combustion chambers, plugs, ring pack and intake valves. My cars seem to run better. Even my old Harley panhead loved the stuff!

    Oh! And I forgot. . . Didja change the thermostat ?!?
     
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  9. Ross Wooldridge

    Ross Wooldridge Senior Member FCBO Gold Member

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    Thermostat works perfectly, and running temps are all good. No need to change it at this time, but the car is scheduled before winter-sleep to get a rad fluid flush and replacement, and a brake fluid flush and replacement.

    So - how often did you add the Marine 2-cycle oil described above? Once or twice a season, or every fill-up?

    Regarding Seafoam - there are a number of Seafoam products... is it this one you mean? Sea Foam Motor Treatment | Oil & Fuel Additive | For Gas & Diesel

    It claims to do the job of "carbon cleaning" at one supplier website, and on the Seafoam website it says it "cleans intake valve and chamber deposits" which I take to mean carbon deposits - and I can get it locally. If that's the product you're referring to, let me know. I may choose to add a can or two.
     
  10. Ripinator

    Ripinator Senior Member

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    Ross: I was just kidding about the thermostat. . . As regards the Marine 2-Cycle oil with TC-W3: I add it every time I buy gas - one ounce to every five gallons. The first time you use it, fill up the tank and add five ounces to the tank (23 gallons requires five ounces - rounded up). The SeaFoam I have not used personally, but I have heard that a lot of people have used it, and it was effective. Can't hurt to try it. . . Some people pour the SeaFoam a little at a time directly into the mouth of the carburetor while the engine is running, and others just add it to the gas in the tank. BTW, you are using 93 octane gas, aren't you?
     
  11. Ross Wooldridge

    Ross Wooldridge Senior Member FCBO Gold Member

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    I'm easily kidded... :canada:

    Yes - PetroCanada 93 Octane, although it has ethanol in it up here. I was running the Shell 91 which has none, but detonation seemed worse than with thet. I will try it again after I run the Seafoam to clean out the carbon, and then the 93 again, then see if I need to add octane booster.
     
  12. Ripinator

    Ripinator Senior Member

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    Ross: If everything is right with your distributor and the carbon build-up, you should be able to run just fine on 93 octane. Both of my '66 TNT cars run fine with no pinging.
     
  13. Ross Wooldridge

    Ross Wooldridge Senior Member FCBO Gold Member

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    Hopefully! That's where I'm going with all this...
     
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  14. mr. fix it

    mr. fix it Old Man with a Hat

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    Ok smart ass.:lol: Have you checked for any excessive slack?
    This can contribute to the issues you have as well...

    checking for carbon deposits is a good thing to investigate as well.
     
  15. Ross Wooldridge

    Ross Wooldridge Senior Member FCBO Gold Member

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    Lol... that I can be!!

    I won't be inspecting the chain at this time unless something truly odd starts happening. Pulling the cover to inspect is an enormous job I won't be doing at this time... the car generally is running excellently and if I were to do that I'd be pulling the whole motor for a refresh and beautification.
     
  16. twostick

    twostick Senior Member

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    You can check for excess slack quite easily. Get a socket and turn the engine backwards. Pop the distributor cap off and watch the rotor as you rotate it slowly forward. The crank should barely rotate before the rotor follows. I've seen them bad enough that the crank rotated from 12 o'clock to past 2 o'clock before the rotor ever moved but that engine ran just awful.

    If it didn't like Shell 91, try some others or try the same station again. It wouldn't be the first time the premium tank got filled with 87 by mistake. Something else that can happen is the 87 tank won't hold all the truck brought so the extra gets dumped in the 91 tank.

    Pioneer used to have premium that would tolerate some compression but I haven't had anything that needed it in a while so I can't say now. Throw $20 in the next time the needle is approaching E and see how it behaves.

    Toluene is the active ingredient for most octane boosters so just shop around to see if you can buy it by the gallon. Google toluene and octane booster for info on mix ratios. I seem to recall 20% being the edge of diminishing returns.

    160 deg thermostat will help if you're running a 190.

    I don't know what carb you're running but if there is any way to tweak your light cruise/transition AFR a tick richer it might stop that rattle. Is it at steady cruise or just at the transition to accelerate?

    Kevin
     
  17. mr. fix it

    mr. fix it Old Man with a Hat

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    Well you don’t need to pull the cover
    You find TDC in the normal rotation of the engine then turn it the other direction and watch the number of degrees it takes to feel the camshaft engage

    it can take a few tries to get a feel for it
    If there’s more than 4 degrees then it has some slack and if it’s really excessivelike 8-10 degrees then it’s time to replace
     
  18. 1970cat

    1970cat Senior Member FCBO Gold Member

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    i've had good luck with marvel mystery oil. i set the carb on high idle and dribble it in until it bogs down. i let the smoke clear and do it again. after about 1/2 bottle it always runs better. it's cheap, easy and wont hurt anything.
     
  19. commando1

    commando1 Old Man With a Hat on the Porch FCBO Gold Member

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    I love this guy.
     
  20. mr. fix it

    mr. fix it Old Man with a Hat

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    We used to use Bardol engine treatment and do the same thing