Technical Tuning help, popping in exhaust..Problem SOLVED!!!!

Ok, here's yet another setback on trying to finish the wagon by Saturdays HRH.
It may be nothing, but it drives me crazy not knowing.

Ok, here's the skinny,

Boring, plain 100% bone stock 350, 97 vortec. Brand new HEI, new Taylor wires, 34 degrees total advance. Brand new Edelbrock 1406, elec choke. Ram horn manifolds, no exhaust yet (going Monday). I have 5 lbs of fuel pressure.

Cam is not going flat, Breaking it in with Joe Gibbs break in Racing oil, high content of Zinc.
Motor has 20" of vacuum, no exhaust leaks, all new vacuum lines.
Also, I have ran the valves several times and checked the firing order 10 times.

When I am trying to bring the motor up to speed, say 2000-3000 rpms, it pops sporadically out the exhaust, I can see flames like an after fire. Seems like it is rich and has unburned fuel dumping into the cylinders. I can see this in the vacuum gauge.

It idles fine. Should I just quit trying to tune until after I get the exhaust finished? I don't know if back pressure has any effect on tuning?

I don't know squat about Edelbrock carbs, is there any tuning I can do without buying a tuning kit?

Thanks in advance......I am burned out on this project, but I am pressing through.

 

Popping into the exhaust usually means a burnt or leaking exhaust valve.
The fire and pop is the leak showing itself on the compression and firing stroke when both valves are closed.
That will also explain the unburned fuel coming into the exhaust.

 

It's a brand new engine. It pops out of both sides equally.

 

Would low voltage mimic this? I just found out the alternator isn't charging either. I was showing 12.7v across the battery. It's on the charger now. I don't know how susceptible to voltage stock HEI distributors are?

 

Check to make sure you have full voltage to the coil could still be wired through the resistor dropping the voltage in the run side of the switch. HEI needs the full voltage or it will pop just as yours is.

 

The problem is that there were a lot of things changed at one time. New wiring harness, new motor/tranny, new suspension, new brake system. It's eating my lunch.

Thanks for the insight. I'm going to see how it runs tomorrow with a fresh charge on the battery.

 

A little moisture under the distributor cap will also make them backfire upon acceleration.

 

Wait until you get the exhaust on. Most engines will do this without exhaust.

 

A lean mixture would cause this. Jetting could be too lean. Do you have the vacuum advance hooked up? If so disconnect and see if your problem disappears.

 

Bump for ya Chris..

 

Mrhp, that's a good idea, I'll try that today.

 

Totally O/T (well, they are engines...) Was at an airshow on Friday, both the P-51 and B-25 would 'pop' and 'bang' at idle, both had short exhaust stacks. Sounded 'neat' to me.

Just sayin'.......

 

You'll need the complete exhaust to make any clearly definitive calls or adjustments.

 

I agree with the thinking that it needs a complete exhaust system before any tuning gets done. I've taken cars to the strip that ran perfect with exhaust in tact, and with open headers had them run poorly. They always needed to be tuned differently for no restriction, so anything done now is a waste of time.

 

Checked the voltage to the coil. 12 volts. The search continues.

 

needs exhaust pipe , unrestricted makes it run lean ...

 

Going tomorrow……

 

Hi root I'm in florida on vacation. I just got your message and J&T automotive in Yukon can align that for you. Dad is in town if you still have problems with that carb after your exhaust is installed.

 

Have fun my friend. I think I can get the alignment close enough to do the run, then I'll have David throw it on the rack when he gets back from Bowling Green.

 

I'll put in with this idea----

 

I pulled the plugs, just like I have done 3 other times. The difference was, this time, I had bought a set of new AC plugs. The previous owner had installed NGK plugs. When I laid the 2 next to each other, the new plugs had a 1/2" longer reach. They were firing up in the threaded area instead of the combustion chamber.

Installed the new plugs, runs smooth.

The moral of the story? Never underestimate stupid people.

 

I just found this thread and was reading through to reply to it and see that you figured it out on your own. Good job. I have seen this a few times. Guys install spark plugs for a regular small block but the vortec heads use a different reach plug, and exactly like you said, the end of the plug wont reach into the combustion chamber. Glad you got it fixed.

 

well that would explain the popping , it wasn't firing all the time ( plug shrouded and ignition when the valve opened ) well atleast you found it before your muffler went on ( great way to make them custom football mufflers .... )

 

I had pulled the plugs but it had not dawned on me to check the reach. I would look at them and put them back in....doh!

 

Had the same experience 45 years ago on a MGB bought together with a friend. Same symptoms. Friend said he checked the plugs - perfect. Couldn't fix the problem so we bailed only to be informed by the new owner about wrong plugs. Hey, if the plug screws in, must be right, correct? No so much. Congrats on your diagnosis. Definitely pays off to hang in there.

 

At least it wasn't as bad as putting a long reach plug in place of a short reach one. I've seen it done before, not a pretty sight.