5.7 vortec popping noise

[1966chevyc20]

Still having trouble with this crate engine. It's a vortec 350 crate engine right from GM. I am running open headers and I can hear a popping noise in the exhaust. Its very audible at idle. Also on deceleration there is excessive backfiring out the headers. It also stumbles on quick acceleration and then picks up and revs. I'm running a brand new summit distributor and wires and AC Delco R44lts sparkplugs. Also, the timing mark jumps around when trying to time it. This leads me to believe a misfire is happening somehow. All wires go to the right plug and are in the correct order at the distributor. I also adjusted the valve lash which didn't seem to help. Anybody got suggestions on what to look for? Pretty sure it's not a flattened cam lobe since it does have a roller cam.
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[geezer#99]

I'm sure it was asked before but what is your timing curve like?
What's initial?
Mechanical?
All in by when?
And what's your elevation?

[1966chevyc20]

Originally Posted by geezer#99

I'm sure it was asked before but what is your timing curve like?
What's initial?
Mechanical?
All in by when?
And what's your elevation?

That's the problem... can't set the timing because the mark jumps around because of the misfire. It has me stumped.
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[geezer#99]

Have you tried a different timing light?

[68gmsee]

Don't overlook the possibility of defective ignition components. I've had defective brand new spark plugs in the past and once a defective dist. cap and rotor.

Re. timing popping sound. First thing you might want to do is to close off or plug all vacuum lines -vacuum advance, power brake booster and any other vacuum ports from the carb (I usually use electrical tape). This will insure you don't have a vacuum leak somewhere causing the popping sound.

[PGSigns]

It will pop and raise cane if the timing is in left field. What are you using for carb and distributor? The open headers will lean the mixture and if you have a short acellerator pump shot that just compounds things. I would gets some pipes on it and sort out your distributor first.
Jimmy

[D.PASSMORE]

I had a similar problem. I was running the Carb just a little bit lean. Re-jetted for more fuel flow. Solved the popping noise, ran a lot smoother. But, like mentioned, eliminate any vacuum lines (plug them off) that could cause a lean condition by introducing more air into the fuel mixture.

[Tom]

Originally Posted by 1966chevyc20

I am running open headers and I can hear a popping noise in the exhaust

Imagine that

-Oem vortec motors will detonate with the factory vaccum advance hooked up, it gives way more then the 32-34* they like.
-Open headers don't help with a stock vortec 350. The cam is smaller then a v6 accord, its not making enough power to justify them. It also will cause issues like leaning out the a/f and popping on deceleration regardless of what you tune.

[1966chevyc20]

Originally Posted by Tom

Imagine that

-Oem vortec motors will detonate with the factory vaccum advance hooked up, it gives way more then the 32-34* they like.
-Open headers don't help with a stock vortec 350. The cam is smaller then a v6 accord, its not making enough power to justify them. It also will cause issues like leaning out the a/f and popping on deceleration regardless of what you tune.

Yes I just finished the exhaust system. Was just running open headers until I got the exhaust system put together. Has a full exhaust system now.
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[1966chevyc20]

Well I adjusted the valves and got the exhaust on and attempted to time it. Timing mark still jumps around. All the plug wires are good and just put in new sparkplugs. Think I might try a new distributor and see if it fixes the problem. Also, when I first ran the engine I was not using a fuel pressure regulator with my electric fuel pump. I am sure I was getting too much fuel pressure at the time. Now I am running a regulator and have it set between 4.5-5 psi. Is it possible that the carb (edelbrock 1405) may have got screwed up from too much fuel pressure? The sparkplugs looked pretty black with soot when I pulled them. I do have a spare 1406 I could throw on there.
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[PGSigns]

They will be very fat at idle with more than 5 psi. The one that was on mine before the efi swap would not clean up at idle till 4psi. The L31 crate engine has a cam in it that was designed for an EFI and is a bit off from a good carb cam. You can make it work but you need to be very aware of your timing curve. Also you need to make sure your distributor has a melonized gear on it for the roller cam. Just any off the shelf HEI is not going to cut it. You need a timing curve of about 14 degrees at idle and 33 to 34 degrees at 3000 rpm and you dont want it to come in real quick. This is checked with the vacuum advance disconnected and plugged. The for the vacuum advance run manifold vacuum and use a vacuum pot that starts to pull in vacuum at about 6" and has 10 to 12 degrees advance in by 13 to 14 inches. I ran an MSD ecurve so for me it was just turning the dials to get this curve and it ran fine with it for more than 20,000 miles. Having to do it with springs, weights and a vacuum pot can be done just takes a bit of time. What ever distributor you put in it put an advance kit in it with all new bushings and springs and a vacuum pot. You can get the adjustable pots and they make it much easier to get what you need.
Jimmy

[1966chevyc20]

Well I got her going smooth as can be!!! Turns out something was wrong with the brand new summit distributor. Ordered the speedway distributor made for factory roller cams and slammed it in and it runs amazing. Thanks for all your guys' help!
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[68gmsee]

Originally Posted by 1966chevyc20

... Ordered the speedway distributor made for factory roller cams and slammed it in and it runs amazing.... Posted via Mobile Device

Good to know. I wasn't aware there was a distributor specific to roller cams. I wonder what the difference is? Anyone know?

Disregard question. I just reread PGSigns post on HEI melonized gear for roller cam.

[GASoline71]

Mellonized gear? That's all I could think of.

Sounds like the other distributor was the problem... just got lucky.

Gary

[D.PASSMORE]

Originally Posted by 1966chevyc20

...Ordered the speedway distributor made for factory roller cams and slammed it in and it runs amazing...

I orderd my distributor from Davis Unified Ignition (DUI). It is setup for that crate motor (no- mods). I'm going to run a Holley Carb on mine. Hopefully it goes without any crazy issues.