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Thread: General engine miss fire question

  1. #1
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    General engine miss fire question

    The thread below made me think of this question and to not hijack the other thread I'm asking here.

    https://karting.4cycle.com/showthrea...918#post730918


    I always forget which is correct for the following statement.

    1. If it pops out the exhaust retard the timing a little and if it pops out of the intake advance the timing a little.

    or is it ...

    2. If it pops out of the exhaust advance the timing a little and if it pops out of the intake retard the timing a little.

    I think #1 is a correct generality if you fire it up without getting the distributor in close enough and need to fudge a little to quickly get on the track, is it?

    And yes like the cam question in the thread I referenced a distributor in 180* out will pop and bang too. I think #1 is true even when only needing to deal with one cylinder, not eight and it does make it pertain to karting too. ... maybe ...

  2. #2
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    Paul
    I'd be looking at many other things other than ignition timing when dealing with a miss.
    However, if it stumbles and backfires out the intake and i suspected the ignition timing was wrong i'd compare it to specifications rather than just start making seat of your pants adjustments.
    Once you know the ignition timing is correct you move on to other things. Checking the ignition timing usually doesn't cost anything. Changing 8 spark plugs, 8 spark plug wires, carb, ignition coil, camshaft etc are all going to cost something.
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  3. #3
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    "However, if it stumbles and backfires out the intake and i suspected the ignition timing was wrong i'd compare it to specifications rather than just start making seat of your pants adjustments."

    Ok you not only "suspect" but you darn right know it's off a little. Do you bump it ahead a little to get on the track being you know everything else is right or do you retard it a little. You ARE going to loosen the distributor/ok flywheel and move the timing a little, should you move it to advance it or retard it depending on which end of the engine is popping?

    I seem to remember it's opposite of which end is making noise. But then again I'm thinking if it's coming out the back retard it instead of advancing it. Brian, you proly know we've done it many times in the past usually going the wrong direction first ... Then your absolutly sure you'll know which way to move it next time, but... then ya forget which way you went the last time. ...

  4. #4
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    I seem to remember it's opposite of which end is making noise. But then again I'm thinking if it's coming out the back retard it instead of advancing it. Brian, you proly know we've done it many times in the past usually going the wrong direction first ... Then your absolutly sure you'll know which way to move it next time, but... then ya forget which way you went the last time. ... [/QUOTE]

    I would guess that if it's popping out the exhaust you would advance the timing because your flame is still burning as the exhaust valve opens - so you need to ignite it sooner. Then the opposite.

    However I would also guess that if you're timing is far enough off for those things to happen it can't be running very good???

  5. #5
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    ahhhh haaaa, maybe this is it. When it pops out the exhaust then your lighting the fuel too soon before overlap is finished. And ... maybe it then means just the opposite. pops out the exhaust you retard the ignition??? <<<< I'm thinking that is correct as far as popping out the exhaust goes but this old fart forgets tooooo fast too much stuff. ...

    thank you for the conversation


    paul


    edit: If that's correct then wouldn't it be the same for a single cylinder engine popping out the exhaust when all else is ok???

  6. #6
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    And don't forget,,,,, these little engines fire on overlap too.

  7. #7
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    Never heard it said that way. I'm voting #2.
    But then if I have the distributor / mag , loose , why not just turn it where it runs best. Then that's hard too do on a Sprint car with push start.
    When ya get the correct answer better make a poster for the tool box.
    Last edited by flattop1; 4 Weeks Ago at 07:49 PM. Reason: Add

  8. #8
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    Quote Originally Posted by paulkish View Post
    ahhhh haaaa, maybe this is it. When it pops out the exhaust then your lighting the fuel too soon before overlap is finished. And ... maybe it then means just the opposite. pops out the exhaust you retard the ignition??? <<<< I'm thinking that is correct as far as popping out the exhaust goes but this old fart forgets tooooo fast too much stuff. ...

    thank you for the conversation
    Paul, if it lit off at overlap you would light your incoming fuel charge also and blow the air filter off, wouldn't you? Just my thought...

  9. #9
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    If the timing is so far off that it is backfiring out of the intake you better retard it or you are going to have a holy piston or blown head gasket etc.
    A lean condition would be my first thought. Although not a conclusive test, try it with the choke partially on.
    Next would be ignition related but not timing.
    Checking the valve clearance doesn't cost anything.
    The ignition firing on the exhaust will not cause any problems. You've already go a major fire going on inside the engine.
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  10. #10
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    I think Paul is talking about a sbc in a sprint car with a Frenches clamp arrangement, designed so you can just drop the distributor in and timing will be correct.

    If you are off 1 tooth at the distributor/cam gear, the result will be as described. He is trying to figure which way it is off from the cues the engine is giving.

  11. #11
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    [QUOTE=Marcis71;731043]
    Quote Originally Posted by paulkish View Post
    ahhhh haaaa, maybe this is it. When it pops out the exhaust then your lighting the fuel too soon before overlap is finished. And ... maybe it then means just the opposite. pops out the exhaust you retard the ignition??? <<<< I'm thinking that is correct as far as popping out the exhaust goes but this old fart forgets tooooo fast too much stuff. ...

    thank you for the conversation

    Paul, if it lit off at overlap you would light your incoming fuel charge also and blow the air filter off, wouldn't you? Just my thought...
    Maybe not if you have mechanical fuel injection? ...

  12. #12
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    Most single cylinder 4 cycle industrial engines fire the spark plug during overlap.

  13. #13
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    So further contemplating has led to this if the mag is advanced one tooth then the rotor is going to be advanced. And vice versa for retarded one tooth.
    Now I need to contemplate the effect that's going to have. Think I'll change too option one.
    Hopefully Mr . Carlson will chime in.
    Last edited by flattop1; 4 Weeks Ago at 12:04 AM. Reason: Add

  14. #14
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    Virtually all the early automotive distributor less ignition systems use a waste spark ignition system.
    Example: GM 2.3, 2.8, 3.1, 3.8 etc liter engines.
    If the timing is set at any amount before BTDC it will also fire at the same # of degrees during the exhaust stroke.
    The fuel charge has already been burning for some time during the exhaust stroke. The tiny wasted spark at the plug will add nothing to the already almost complete combustion.
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  15. #15
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    The rotor has to be at the right place to point and shoot electricity to the terminal on the cap. If you slip the mag in one tooth out then it's not going to be pointing inside at the cap terminal. Sure you can in theory rotate the cap to make up for being off one tooth, but the nature of it is everything else just won't line up and be where it needs to be. Like spark plug wires will not be in the right place etc.. You either have to have stuff right or fudge a 'lot' of other things. At this point we've done just about everything wrong at least one time even burning a hole in a piston starting an engine for the first time because of not having the barrel valve set correctly. Now... we just know how to set a barrel valve and the why's of it and do it correctly. Same with most everything else.

  16. #16
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    I guess i should have followed the link to the other post.
    My apologies to everyone.
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  17. #17
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    Quote Originally Posted by paulkish View Post
    "However, if it stumbles and backfires out the intake and i suspected the ignition timing was wrong i'd compare it to specifications rather than just start making seat of your pants adjustments."

    Ok you not only "suspect" but you darn right know it's off a little. Do you bump it ahead a little to get on the track being you know everything else is right or do you retard it a little. You ARE going to loosen the distributor/ok flywheel and move the timing a little, should you move it to advance it or retard it depending on which end of the engine is popping?

    I seem to remember it's opposite of which end is making noise. But then again I'm thinking if it's coming out the back retard it instead of advancing it. Brian, you proly know we've done it many times in the past usually going the wrong direction first ... Then your absolutly sure you'll know which way to move it next time, but... then ya forget which way you went the last time. ...
    You have GOT to be kidding me!!

  18. #18
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    Quote Originally Posted by Jimbo View Post
    I guess i should have followed the link to the other post.
    My apologies to everyone.
    i enjoyed reading what you offered. No apology needed. ...

    Learned from it too.

  19. #19
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    If you have the points just starting to open as the rotor points to the number 1 spark plug on the cap at your desired ignition timing (38*?), then you will be close enough to rotate the mag in the clamp to time it with a light once the engine is started. (If you've got a buzz-box, that'll simplify things a ton.) You must have a timing mark on the pulley (or water pump if running no belt drive on the front with a KSE front cover and water pump). You can find TDC in #1 cylinder by simply pulling that spark plug and listening to the air coming out as the piston rises. Again, that'll get you close enough to drop the mag in and get it running. Then turn it either way to get the timing light points to match up.

    FWIW, we broke the shaft in a mag in our car and had to change it at the track Saturday night. I didn't realize how rusty we were at it - Took a couple of tries as we put the cap on backward once -- the popcorn should have been a tell-tale sign that something was wrong. Kinda spoiled by the MSD back when I hung up the helmet.



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  20. #20
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    I always used a buzz box, set #1 at TDC, dropped the mag in and set the points with a buzz box, and set timing at 36*....with a locked advance mag.

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