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Popping from exhaust

2K views 13 replies 10 participants last post by  VolpesVisions 
#1 ·
Hello all, I am hoping someone on here can help me out. It's my first classic that is all me and I use this forum a bunch to help me build it from top to bottom. I have a 1970 chevelle malibu sedan with a 1974 four bolt main 350 which is attached to a powerglide two speed. That powerglide is actually being replaced with a TH400 once I find a shop that can cut my driveshaft. ANYWAY, the motor has only run once and it died on me in the middle of a field so I rebuilt it, now when turning over I hear faint pops out of the exhaust and sometimes a big backfire, but it doesn't smart. Smells like a firecracker too. I am wondering if any of you have seen this and if you think this is timing or valves or something worse.


I apologize if this is going in the wrong area, I am new to posting to forums as a whole.

Thank you!!
 
#2 ·
since you rebuilt it, it could be a number of issues from ignition timing, to valve timing, to a pooched valve or seat. Or even a bad cam. Why dont you give us more info. 1st thing I;d check is timing, both valve and ignition.
 
#5 ·
Thank you all for your ideas, I was unsure if anyone would get back to me, let alone so quick. To answer a few questions
1. It is a points MSI Distributor, Edlebrock intake with a 1406 4bbl carb, dual headers, edlebrock fuel filter.
2. Tune and everything are close to factory, I am not going for a driftcar here, just a Sunday driver.
3. This is the second time the motor was rebuilt, I am unsure of the specs of the first build, (bore over, head type, piston size, ect.) I know this because when tearing it down Everything looked almost brand new besides for carbon buildup.
4. It has not run since rebuilt, just put it in the car about a month ago, I am a 'shade tree mechanic' who is a full time college student and full time Network Engineer

I had a feeling it could be valves, I have done the valves over about 3 different times, two times by the book, TDC intake ect. then once using my grandfathers method of tighten until there is no slack, then rotate engine 90 degrees, retighten if needed, 1/4 of a turn when done 4 revolutions. This is not my first motor build, it is my first classic motor build however, meaning I built a 5.7L Vortec and a 4.3L I6 Vortec (Silverado and Trailblazer). For timing I believe I am set up so the dots are both at 12:00 and my distributor has #1 facing the #1 cylinder.
 
#7 ·
Try declining the timing a bit while someone cranks the engine with the key. Dots at 12 and 12 means #1 firing so I doubt that's your issue. You may have a bad condenser.
 
#8 ·
Popping out the tailpipe is usually caused by a misfire that allows fuel to collect in the exhaust and then it ignites. We used to shut off the car in gear and turn it back on to make a real big bang. A lot of fun until it starts opening up the muffler cases and then it gets expensive. If it pops when you let off the fuel that can be caused by a lean condition or even an exhaust leak. Engine timing will usually cause a backfire up through the carburetor. I suspect you have fuel dumping into the exhaust system via a dead cylinder, wire, plug, cap etc....
 
#12 ·
Without taking it apart I would turn the crank 360* and set the timing mark on the damper to 0 on the timing tab. Then put the distributor back in with the rotor facing #1 cylinder and keep your fingers crossed that the dots aligned properly after you turned the crank the 360*. From my other post #6 the way you had set the dots up both at the 12 o'clock position when you put the distributor in it was off 180*.
 
#13 ·
Have you tried lifting the distributor enough to turn from #1 to #6 ? bring the rotor around to TDC #1 then pull up the dist. and change to #6, if you're 180 out that will get you closer to being able to time the engine
 
#14 ·
Wow guys, I want to thank you for all the help you gave on this issue. My issue was that it was a class ID10T error on my part. When setting TDC I did it incorrectly just to get it done a while back, however I took off the valve cover, watched the intake, then set TDC the right way. Then I dropped in the distributor as per normal and after some fine tuning adjustments the car fired right up. Unfortunately I forgot to torque down the Intake bolts to spec as the engine was rebuilt about a year ago, which means I made a mean coolant oil milkshake. Not a big issue, cleaned everything up, checked on torque specs and put new oil and shes running like factory.

Again I cannot thank you all enough!!


:grin2:
 
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