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Rough running back firing 350

Discussion in 'Pacific Region' started by sr175, Apr 15, 2004.

  1. sr175

    sr175 Registered Member

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    I have a newly rebuilt 350 motor that is exhaust backfiring while accelerating. Seems to run alright while its warming up. My current timing is 12 deg BTDC. I have a newly rebuilt holley carb on there as well. Any ideas?
     
  2. Topdown

    Topdown 1/2 ton status

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    ooh... toughy... I am guessing here... I would say check the choke and make sure that its turning off.

    make sure its not running to rich. Also, I would back your timing down a coupe of degrees... between 8 - 10

    Just my thoughts...
     
  3. sr175

    sr175 Registered Member

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    The choke is a manual choke and is open all the way. At first I had it in the 8-10 range but seemed to run pretty rough. I'll try going back down to that and play with mixture some. You suppose it is a little rich for being so advanced?
     
  4. kennyw

    kennyw N9PHW Premium Member

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    How old is your vibration dampener? I have heard many stories of them seperating and the part with the timing marks rotating so that the timing was way off.
     
  5. sr175

    sr175 Registered Member

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    I got the vibration dampener used. I would say its got a few years under its belt. I've not heard that one before and is interesting as I have seen the outer part flex when taking one off a motor. If the outer part turns I couldn't imagine it off by more than a degree or two? This may explain why I need to be so far advanced at 12? I am going to back off the timing to between 8 and 10 like the previous post. Not sure if I will get to that tonight or not. Work gets in the way of working on the truck!!! But is helpful in paying for all the parts /forums/images/graemlins/thumb.gif
     
  6. kennyw

    kennyw N9PHW Premium Member

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    Do you have a vacuum guage? Try timing it by a vacuum guage instead (just gonna need to ask someone else how to do it). Then double check where the timing light is after words. You may find the harmonic dampener off by 5-10 degrees or more.
     
  7. sr175

    sr175 Registered Member

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    I may have access to one and you are right! I would have to ask someone how to do it that way. I am unfamiliar with that way of doing it. That's quite a bit off! Just as easy to swap it out with another dampener though to see...
     
  8. ntaj*ep

    ntaj*ep 1/2 ton status

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    May have valves adjusted too tight, seen that more on "new" motors than anything else.....
     
  9. ntaj*ep

    ntaj*ep 1/2 ton status

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  10. sr175

    sr175 Registered Member

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    That procedure is similar with some nice additions as the manual and it works great. I did this a couple times because when I first put the motor in it just would not run well. I redid the rocker/valve adjustment and it worked like a charm (the couple tries because I found out what happens when it is too tight, you made good point about loosening it up so the rod slightly goes up and down not just turning it). I just have this back firing after the motor warms up. It does have the normal hydraulic rockers and should be somewhat self adjusting.
     
  11. ntaj*ep

    ntaj*ep 1/2 ton status

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    OK, well the only other thing I could think of would be the ignition timing being a tooth or two off.
     
  12. kennyw

    kennyw N9PHW Premium Member

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    [ QUOTE ]
    OK, well the only other thing I could think of would be the ignition timing being a tooth or two off.

    [/ QUOTE ]

    If the timing marks are good this would not be the case since you can just turn the distributor housing to make up the difference. Just makes me think the timing marks are not where they should be.
     
  13. ntaj*ep

    ntaj*ep 1/2 ton status

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    Thats not always the case, even if the marks line up you can still be a tooth or two off. You can't just set a distrubitor in anywhere /forums/images/graemlins/thumb.gif
     
  14. kennyw

    kennyw N9PHW Premium Member

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    Here is a test for you:

    Put a timing light on your engine and check your timing. Then pull your distributor and drop it back in a tooth off. Then check the timing light again. It wont be in the same place but if you adjust it (by simply rotating the distributor) back to where the timing was the truck will run exactly the same.

    The rotational orientation between the rotor and distributor cap (as well as the pickup inside the distributor) does not care what tooth on the cam is currently in mesh. Buy being a tooth off the relationship between the dist. cap and pickup is still the same.

    The only problem that arrises from being a tooth off is mechanical interference of trying to rotate the housing back into the correct timing position as long as you dont move anything internal to the distributor.
     
  15. ntaj*ep

    ntaj*ep 1/2 ton status

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    [ QUOTE ]
    Here is a test for you:

    Put a timing light on your engine and check your timing. Then pull your distributor and drop it back in a tooth off. Then check the timing light again. It wont be in the same place but if you adjust it (by simply rotating the distributor) back to where the timing was the truck will run exactly the same.

    The rotational orientation between the rotor and distributor cap (as well as the pickup inside the distributor) does not care what tooth on the cam is currently in mesh. Buy being a tooth off the relationship between the dist. cap and pickup is still the same.

    The only problem that arrises from being a tooth off is mechanical interference of trying to rotate the housing back into the correct timing position as long as you dont move anything internal to the distributor.



    [/ QUOTE ]

    This is the last I will post up about this topic.
    Try timing a motor with a 5 gas analizer, vac. gauge, and a timing light. It will not, not, not, be the same. Its like a motor that has a timing belt with a mechanical tensioner, if you deck the head and take too much material off the marks will line up but it will run like poop. Its a plain and simple fact. Put your dist. in with the vac. advance pointing the fire wall and tell me what your emmissions reading is with the timing set "correctly" Then put it back to where it "should" be and tell me what the readings are. I don't mean to offend but I have been fixing "back yard" projects for sometime now, (and yes I have learned from my many many mistakes in the back yard) I know sometimes what I say sounds like complete crap, I most likely said the same things until I tryed it out and......blamo the impossible problem is now fixed. So no disrespect meant but trying to fix problems on the internet is not an easy thing but I will always try it may sound like crap but so is paying someone else to do what someone has already suggested.
    I find that most people would like to pay someone to fix their junk rather than get the motivation to do it right themselves. I also find that people who say "well mine was doing that and it was...." only make things worse most times, sure its hit and miss but wouldn't you rather know something is bad or just keep replacing parts until taking it somewhere didn't sound so bad?
     
  16. shane74

    shane74 1/2 ton status

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    Well...actually....you kind of can...

    If the #1 piston is TDC, you can dang near drop the dist in anywhere in the rotation as long as you connect the #1 wire to whatever terminal the rotor is pointing at. Then you start your firing order rotation from there. Trust me...It works! /forums/images/graemlins/yikes.gif I agree, it's NOT the way it was designed, butit works /forums/images/graemlins/smirk.gif

    I just felt like stirrin' up some chit! /forums/images/graemlins/histerical.gif /forums/images/graemlins/whistling.gif /forums/images/graemlins/weld.gif
     
  17. POWERMAD

    POWERMAD 1/2 ton status

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    Jeez what a ****aroo..
    Roll #1 to TDC, back it off and roll it till it hits 8*BTDC.
    With the cap on mark the distributor where the #1 terminal is, drop in the distributor and line up the mark with the rotor.
    I like the distributor to be sitting square and will turn the pump to get it to where I like it.
    As long as you are on 8* on the balancer you can put the firing order anywhere you like.
    Off center with the can against the firewall, or all the way in the other direction.
    as long as the rotor is in line with # 1 it will fire that way.
    I like to do away with all the hassel of wondering where TDC is on the damper by after degreeing the cam or simply lining up the dots is to install the front cover with a couple of bolts.
    Then tape a tooth pick to the hash mark on the damper.
    start to install the damper over the keyway and give it a couple of taps to be sure it is seated correctly.
    Then it is a simple matter of seeing if the pick is lined up with the TDC tab on the cover.
    If not either get timing tape or an adjustable tab.
    It almost sounds like there is not enough timing.
    I would make certain that the distributor is not gummed up and unable to advance, advance springs worn out, vaccume can bad, vaccume leaks.
    It may have to be timed by ear if the damper has spun , advance 2 deg and nail it uphill. Keep doing that untill it starts to ping and back it down till it quits.
    I totaly agrre with not throwing parts at it to see if it fixes the problem.
    Costly and a waste of time, I would much rather find the root of the problem and fix it before I just start tossin parts at it.
    SBC's have got to be the blessedly easiest engines to work with.
    Just a few coppers from my way..
     
  18. shane74

    shane74 1/2 ton status

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    [ QUOTE ]
    Jeez what a ****aroo..


    [/ QUOTE ]
    /forums/images/graemlins/histerical.gif /forums/images/graemlins/histerical.gif /forums/images/graemlins/histerical.gif /forums/images/graemlins/histerical.gif /forums/images/graemlins/histerical.gif /forums/images/graemlins/histerical.gif /forums/images/graemlins/histerical.gif /forums/images/graemlins/histerical.gif /forums/images/graemlins/histerical.gif /forums/images/graemlins/histerical.gif /forums/images/graemlins/histerical.gif /forums/images/graemlins/histerical.gif /forums/images/graemlins/histerical.gif /forums/images/graemlins/histerical.gif /forums/images/graemlins/histerical.gif /forums/images/graemlins/histerical.gif /forums/images/graemlins/histerical.gif /forums/images/graemlins/histerical.gif /forums/images/graemlins/histerical.gif /forums/images/graemlins/histerical.gif /forums/images/graemlins/histerical.gif /forums/images/graemlins/histerical.gif /forums/images/graemlins/histerical.gif /forums/images/graemlins/histerical.gif

    I knew that'd get a reaction outa somebody! Sorry dood. Just bein a fawkchop today /forums/images/graemlins/grin.gif
     
  19. POWERMAD

    POWERMAD 1/2 ton status

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    [ QUOTE ]
    Sorry dood.

    [/ QUOTE ]
    /forums/images/graemlins/dunno.gif
    Christ on a cart now I'm confused.
    With the crank/damper on a theoretical starting point it don't matter what position the distributor is at as long as the #1 terminal is lined up with the rotor.
    The cam turns the distributor gear, the pump determines where the rotor is. who gives a sh!t where it is at.
    As long as the crank is at the desired base timing usualy 6- 8 degrees and the rotor is lined up with #1 it don't matter diddly squat where the distributor sits in the block.
    When it matters is when you have to adjust timing and if it is on the firewall then you can not move it.
    Take a long driver and turn the pump for the love of makin things easy.
    The distributor is square and you have plenty of room to adjust if need be.
    Damn talk about makin a project out of nothin.
     
  20. sr175

    sr175 Registered Member

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    Would have to agree with powermad. Square up distributor get firing order right and adjust for 8. Will check mine tomorrow but last I checked it was at 12. The distributor on a 350 can only go in 2 ways because on the pump there is a key. You cannot put it in off by one tooth and get the thing to go down all the way to mount on the 350 (couldn't tell you about fords they suck). Either right on or 180 out. It's obvious when 180 out. I've heard of the chain being of by one tooth but that would be difficult. I've done a lot of adjustments but will continue until right. Thanks for all the posts and will work tomorrow! I'm sure it will work.

    PS- Any of you guys know of a excellent exhaust shop in the Tracy/Modesto CA area that is good priced? Need a whole new setup. Mine sucks and leaks like a sive /forums/images/graemlins/hack.gif. I could also use a new set of headers. But thats another story! $$$
     

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