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timing question !!UPDATE!!

Discussion in 'The Garage' started by Jonny-K5, May 18, 2004.

  1. Jonny-K5

    Jonny-K5 1/2 ton status

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    i bought i rebuilt 350 from a guy for my old p/u. when i hooked up a timing light to it to set the timing the mark on the balancer is way off. where the engine runs good is about two inches before it hits the timing tab. if i try to retard it the thing backfires and floods/dies. how can i get this timing mark to line up with the tab?
     
  2. camok10

    camok10 1/2 ton status

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    Re: timing question

    if you cant turn the distributor enought to get it to line up, it may be a tooth off. take it out and put it a tooth to......i cant rightfully remember which way. but im sure you can figure it out by the way you turn it.

    good luck, and sorry i couldn't be more of a help. /forums/images/graemlins/waytogo.gif
     
  3. highrider_44s

    highrider_44s 1/2 ton status

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    Re: timing question

    Pull the #1 plug and turn the motor over till your on the commpresson stroke the see if the timming marks (tdc)line up with the line on the harmonic balancer if they don't make your own mark to line up with the tdc mark and use that to set your timing /forums/images/graemlins/waytogo.gif hope that helps
     
  4. muddbudd72

    muddbudd72 Registered Member

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    Re: timing question

    sounds like the balancer and timimg cover are from different year motors. you can get two different bolt on timing tabs from mr. gasket. just match up the correct one for you balancer. and just cut yours off your cover.
     
  5. husurddy

    husurddy 1/2 ton status

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    Re: timing question

    Just a silly question, but how old? Does it have an electronic spark advance?
     
  6. Jonny-K5

    Jonny-K5 1/2 ton status

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    Re: timing question

    i dont think the timing tab is the problem. the timing mark is too far back to be properly read. i guess its possible the balancer is wrong. the motor is somewhat cobbled together. i was told its a target shortblock with 72' heads. it had an old points style distributor on it but i swapped it out for an hei unit i had laying around.who knows what year the balancer is.

    if i pulled the dist. back out and turn it one tooth back or forward and then adjust the timing, would that line it up? i dont want to pull the valve cover off and start from scratch if i dont have to.
     
  7. Jonny-K5

    Jonny-K5 1/2 ton status

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    Re: timing question

    <font color="red"> UPDATE </font>
    ok i removed the spark plug and turned the motor over, the timing mark is dead on. i played with the timing some more and the thing backfires when its more than 16* btdc. it only backfires when i give it a quick shot on the gas pedal.

    could this be a problem with the fuel mixture? it doesnt backfire at all when its between 16 and about 26* btdc. but it does ping a little in that range.

    what is making this thing backfire and what should the timing be set at? from what i've gathered 4* before is pretty much the standard for these engines. is this what i should shoot for?
     
  8. Smitty

    Smitty 1/2 ton status

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    Re: timing question

    Please don't take this the wrong way. Do you have the light hooked to the front cylinder on the driver's side of the vehicle? It may seem like a dumb question but I ran into this when a friend of mine had the same probem. He had the timing light hooked to the wrong cylinder.
     
  9. Jonny-K5

    Jonny-K5 1/2 ton status

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    Re: timing question

    yep, its the on the #1 wire. /forums/images/graemlins/thumb.gif
     
  10. Jonny-K5

    Jonny-K5 1/2 ton status

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    Re: timing question

    im starting to think its a problem with carburation. i've got one of those holly 500cc 2 barrels on there with an 2 to 4 adapter. its just temporary til i get a good 4barrel to put on it. it hasnt been tuned for this motor so thats why i have my doubts.

    what would make it backfire when you give it a quick shot off idle? idle circuit too lean? jets too big? or is timing the only thing that will make it backfire.
     
  11. highrider_44s

    highrider_44s 1/2 ton status

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    Re: timing question

    [ QUOTE ]
    Please don't take this the wrong way. Do you have the light hooked to the front cylinder on the driver's side of the vehicle? It may seem like a dumb question but I ran into this when a friend of mine had the same probem. He had the timing light hooked to the wrong cylinder.

    [/ QUOTE ]
    also did you disconnect the vaccum advance and plug it off? /forums/images/graemlins/whistling.gif also 16* is a lot for a small block (assuming its faily stock) usually start around 8-12
     
  12. Jonny-K5

    Jonny-K5 1/2 ton status

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    Re: timing question

    I didnt remove the vaccum line, but that shouldnt make a difference if im checking the timing at idle right? the advance doesnt kick it til you rev it up. the engine has an isky 262 cam, around 9 to 1 compression and under 100 miles. i dont know if that cam makes any difference or not.


    the chilton's book i have says most of the 350's run around 4*.you say you start around 8-12* and then move closer to TDC right? is there anything else besides timing that would make the engine backfire?

    ~BTW it backfires thru the carb, not the exhaust~
     
  13. Smitty

    Smitty 1/2 ton status

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    Re: timing question

    I'd pull the vacuum line anyway. You never know if it might have been hooked up in the wrong location.
     
  14. Jonny-K5

    Jonny-K5 1/2 ton status

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    Re: timing question

    i pulled it just to be sure, didnt make a differnce.
     
  15. highrider_44s

    highrider_44s 1/2 ton status

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    Re: timing question

    /forums/images/graemlins/thinking.gifmaby your mechanical advance is kickig in too early or comming in too fast /forums/images/graemlins/dunno.gif do you have a light that will check mechanical advance? if you don't i think msd makes a strip that you put on the balancer to check that with a regular timing light. check your cranking compression with 9-1 you might be around 170-190 ish range so you don't need the mech advance to come in too fast your total mech advance should be around 32-36 and should be all in by 38-4500 rpm /forums/images/graemlins/dunno.gif

    did you say you had a holly?
    can't remember but i think when some of the older holly backfire they blow the power valve out then they won't stop backfiring. this was for the 4bbl not sure if the 2bbl is the same or not /forums/images/graemlins/thinking.gif
     
  16. 4xcrazy

    4xcrazy 3/4 ton status

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    Re: timing question

    I'd play with the distributor some more, it may be a tooth off or so. /forums/images/graemlins/thinking.gif


    OH and yeah, of course that thing with the Holley power valves too,,, /forums/images/graemlins/doah.gif
     
  17. Smitty

    Smitty 1/2 ton status

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    Re: timing question

    Since it seems like you've checked everything else I'd be looking real hard at the balancer. The outside ring may have slipped and this will throw the marks off. They sell a little tool that screws into the sparkplug hole that makes it real easy to find actual TDC. You install the tool and rotate the engine over by hand until the engine stops. Note the location of the timing marks. Then you rotate the engine over in the other direction by hand until it stops and note the location of the timing marks. Split the difference between the two places where the engine stopped and this is very close to actual TDC.

    I don't think the distributor is off a tooth since you can actually get the timing within specs except for the backfiring. I'm guessing that the marks aren't showing the actual engine timing.
     
  18. mrk5

    mrk5 The Sticker Guy Moderator Vendor GMOTM Winner Author

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    Re: timing question

    Backfire through the carb could be attributed to the carb being too lean.

    Here's my opinion. I've been doing alot of research on timing, and this is based on what I'm finding. Timing with a timing light really isn't the most accurate method. Try setting it with a vacuum gage, set initial timing at the highest vacuum. Then back it off 1" of vacuum to prevent detonation. Take it for a drive and check the new settings. If it is requiring such high initial advance, you need to be careful about what the total advance is.

    I have a Demon carb which recommends 18-22* initial advance. The following is the best explanation I've found for why this is:

    [ QUOTE ]
    Due to cam over lap Performance engines make very little cylinder pressure at low RPM, therefore making the fuel very hard to ignite and to burn completely under these low pressure conditions. In order to accomplish a full burn of the fuel supplied, the engine will require enough initial timing to allow time for the combustion process to complete, or a get head start on the piston. This is why initial timing is critical and advance numbers that you've probably never considered are necessary when installing a Demon or for that matter any other performance carb.

    [/ QUOTE ]

    So what I'm saying is that if your engine likes the high inital timing, then leave it be. As long as your not getting any detonation, it should be okay.
     

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