Backfiring after shutdown

Discussion in 'Engine Topic' started by Johnboy9914, Apr 23, 2008.

  1. Johnboy9914

    Johnboy9914 New Member

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    I just started my engine after several months of putting together. I ordered the shortblock from AutoZone, had the heads redone at the machine shop. I installed all new push rods, valve springs and roller rockers. Everything else is brand new. I swapped out the oil pump that came with the engine for a Melling HV oil pump. Everything seems to be working fine. The engine fired up immediately and ran much smoother than I expected. I only ran the engine for a couple minutes (mostly to burn in the paint and check for leaks. I have not adjusted the timing yet but can tell it is very close to TDC. Like I said, idle is exceptionally smooth. After a couple minutes (no more than three minutes for sure) I noticed 5 of 8 of my ceramic coated headers were beginning to glow cherry red. The engine is producing approx. 73 pound of oil pressure and water is circulating throughout the engine. After the third time I started and shut it off it backfired after about 3 - 5 seconds. I started and shut it off three more times (after allowing the engine to cool a little), all three times it backfired through the exhaust 3 - 5 seconds after shutdown. I pulled the valve covers, loosened all of the rocker arms and (starting from scratch) adjusted all of the valves. I'm using hydralic lifters. The engine sat for about 1.5 hours before starting one last time before turning in. The engined fired right away, ran very smoothly and after about two minutes I noticed the headers starting to glow again and shut it off. After about 3 -5 seconds it backfired. Now I'm beginning to worry the engine is not getting water and oil aound the heads to properly cool the engine. I have not ran the engine more than a couple minutes at a time and have only started it 8 times. I can probably figure out the backfire, but I'm really concerned about the glowing headers. Has anybody else experienced this problem? I don't want to run the engine again until I have something to go on. Any suggestions will be greatly appreciated. The engine is a 350 bored 40 over, stock pistons, mild cam 78cc chambered heads (from an old Chevelle), new edlebrock 650 carb with electric choke, and a performer high rise aluminum intake.
     
  2. muenk79z28

    muenk79z28 Veteran Member

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    Timing is probably way retarted.. .usually causes glowing headers b/c of all the unburned fuel being burned in the header rather than in the CC... Will also cause the exhaust to burp a couple times too after shutting it off..
     
  3. Bikefixr

    Bikefixr Veteran Member Lifetime Gold Member

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    You are either VERY lean on the mix, or your timing is waaay retarded. When that happens, unspent fuel flows into the header and continues to burn there. Reset your timing and check fuel mix.
     
  4. Johnboy9914

    Johnboy9914 New Member

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    Thanks! I restarted the engine and set the timing dead on at TDC. The engine idles so smooth w/choke at about 1000 RPM. After a couple minutes of running the header pipes for 1,3,4,7 and 8 became cherry red again. I shut it off after a couple of minutes. Low and behold it backfired after about 3 seconds. Even if I'm off one cog on the distributor, if I have the timing mark on TDC shouldn't it be, in fact TDC. Now I'm worried I doing damage to the valve train and cam. Before starting the engine I screwed the adjustment screws on the carb all the way down and backed them off 1 and 1/4 turn. Any help would be appreciated. I'm at a loss.
     
  5. Twisted_Metal

    Twisted_Metal Administrator Staff Member Lifetime Gold Member

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    Recheck your plug wire order.
     
  6. gwrba

    gwrba Veteran Member

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    mmm

    sounds like muenk and Bikefixr said.... you're out of timing....

    Do not worry about the TDC mark on top of your balancer.... it could be wrong.. Two weeks ago i started my 71 after three years of being sat... Following that procedure, you'll never have problems.

    1) Disconnect all the wire plugs from your spark plugs

    2) Remove the driver's side valve cover

    3) Remove all the spark plugs ( you'll be freeing the engine from any compression by that way so you can turn it very easy).
    3) Get a torque wrench and a proper socket and attach it to the main pulley ( it's pretty easy using a torque wrench).. you'll be rotating your engine clockwise and anticlockwise.
    4) By using a LONG screwdriver, and with much CARE ... put the screwdriver inside the bore of the number 1 cyl, through the spark plug hole
    5) Slowly .... turn the torque wrench on the clockwise direction while you're holding the screwdriver until you feel some pressure and you cannot move the torque any more... do this step SLOWLY .. if not, you can scratch your piston......
    6) You can be at TDC or you can be at 180 degrees off... To check this, simply turn the torque anticlockwise a bit, and repeat the operation clockwise to see if the number 1 cyl exahust valve is getting CLOSED . If it's going OPEN ( rocker arm pushed ) then you're 180 degrees off..
    On the other hand, if the number 1 cyl intake valve is getting CLOSED, then you're on TDC ! ( or really closer )
    7) At this place, remember to do a mark on the balancer and the tab, so you can remember where your TDC is really.

    If you're 180 degrees out, turn anticlockwise a bit, remove the screwdriver, let the piston go down, insert the screwdriver and repeat the steps 5 and 6 one more time... the next time, it'll be TDC for sure.

    8) Rewire your spark plug wires in the correct order... and turn the dist a bit in the anti-clockwise direction (very little) so you retard a bit your ignition ( just a bit... if i remember well, you have to be near 4BTDC)

    9) If your engine starts and doesn't back-fires anymore... Use a timing light to set the exact timing.

    Maybe it's not the perfect method for find the TDC, but it worked really good for me.... I also had a bad TDC mark both on the balancer and on the tab, so i had to do it.

    Hope this help you.
     
    Last edited: Apr 23, 2008
  7. Johnboy9914

    Johnboy9914 New Member

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    Thanks, I'll check TDC again. The only time it backfires is after shutdown and only once. Ususally about 3 - 5 seconds after the engine shuts off. I've rechecked my plug wires. Luckily, I've got a running camaro to compare it to. Hopefully I'll find the problem soon. I hope I haven't damaged the new cam and lifters with all the starting and stopping. I've yet to let it run more than a couple minutes at a time, mainly because the pipes get so red. It's really wierd that only 5 of the 8 pipes turn red and usually after just a couple minutes of run time. I'm going to connect a temperature gauge to the top of the engine so I can monitor. I've adjusted the valves twice and I know they are correct. Puzzled?
     
  8. gwrba

    gwrba Veteran Member

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    Hi JohnBoy

    How Did you adjusted the valves ?

    It's always important to do a cold adjusting of the valves(engine cold ), followed by a hot adjusting(engine running).. if you only did adjust the valves with the engine on, you have for sure the job done at a 50%.

    as far as i know .....The temperature shouldn't be a matter, even if you haven't water on your radiator, just for a few minutes of running the engine..... except the case that you have a timing/valve train issue that could turn your engine SO hot that your oil gets SO hot.

    The matter that the engine backfires only after shutdown.... i agree that the problem is a retarded ignition... when you've your engine running, it simply doesn't backfires, 'cause the dist weights are working and they add centrifugal advance.... so you're not so retarded.... BUT when you shut off your car, they're not working at all....

    What is your idle RPM reading... ? Maybe you're running your engine at a high idle rpms... so your problem cannot be evident neither at idle or at off-idle...
     
    Last edited: Apr 24, 2008
  9. Johnboy9914

    Johnboy9914 New Member

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    When I initially adjusted the valves I followed the chart in "How to build a small block Chevy". At TDC, with the intake off and able to watch the lifters, I indexed the balancer with eight equal portions. At TDC I adjusted the valve it called for. Using my fingers to rotate the pushrod clockwise and counter clockwise until I began to feel resistance, then applied 3/4 turn of the wrench. From there I went to the next mark on the balancer and adjusted the valve on the chart...by the time I turn the engine nearly two complete revolutions I had adjusted each valve accordingly. When I rechecked the valves (after starting it 6 or 7 times and waiting about 1.5 hours to cool down), I brought the number one cylinder to TDC (I pulled the plug and bumped the engine over, with my thumb over the hole, to make sure I was on the compression stroke), removed both valve covers, loosened all the nuts on the rockers and brought the #1 exhaust valve to a point of just openning and adjusted the intake valve for #1. Working the drivers side only, I bumped the engine again until the #1 intake valve was almost closed and adjusted the #1 exhaust valve. I did this with all the cylinders, one cylinder at a time. I have an old set of chevy valve covers that I've removed the center out of (in order to adjust while the engine is running, and warm and won't throw oil all over the place). I'll play with the timing a little more this evening. I must be off at least two cogs when I compare to my other camaro distributor. The engine, starts right up and runs very smooth. Idle is about between 1000 and 1100RPM w/electric choke. I haven't ran the engine long enough to for it to turn off yet.
     
  10. gwrba

    gwrba Veteran Member

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    Hi

    I'm not completely sure if the procedure you were using to adjust valves is 100% efficient.

    See the following link:
    http://www.centuryperformance.com/adjusting-valve-lash-spg-149.html

    It explains you how to adjust the valve lash correctly. It worked for me!

    Please read it and follow it, re-adjust all valves by using that procedure.

    If it's a valve lash problem... it will be SOLVED.

    I forgot to mention: do the following test: using a screwdriver, loose the idle speed screw a little on the carb, until it's near closed.... and see if a backfire occurs when you're doing it... and let me know the results!!

    Keep in touch!!
     
    Last edited: Apr 24, 2008

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