Tuning help! 383 popping on acceleration - Chevy Nova Forum
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Old 6th-November-2019, 09:03 PM   #1
chevyfan
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Tuning help! 383 popping on acceleration

Need some help fellas. Heres the scoop, fresh 383 rebuild trying to get it tuned! The car idles and starts fine. Off idle feels good. But above 3k rpm on acceleration this thing pops out the exhaust and hesitates. Quick motor specs:
383, afr 195 72cc, flat top, 750dp, howards retro roller 286/294, single plane, 9.8:1 comp, petronix 3 dist, msd coil. Some stuff ive already checked:
Timing: tried 34 up to 38, with loose springs
Carb: Havent changed since the rebuild but cleaned and confirmed floats,
Firing order,
plugs,
rechecked valve adjustment, 3/4 turn after zero lash
The engine ran great before the rebuild and not much changed. Just New rings, bearings, and retro roller conversion.
why would it run ok down low and like **** up top?
Thanks
Shawn
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Old 6th-November-2019, 11:17 PM   #2
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Check the advance in distributor
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Old 6th-November-2019, 11:26 PM   #3
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new curve kit? was thinking that too. the springs look fairly worn too. I had the lightest springs on board too. think it was all in by 3000
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Old 7th-November-2019, 11:47 AM   #4
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I do have a couple questions...
When does the engine hesitate and backfire?
A - When you accelerate from a stop... and as you are still accelerating, the engine reaches 3000 rpm and you start to experience these issues?
B - You are already cruising at 3000 rpm... then hit the accelerator pedal and the engine immediately hesitates and backfires?

When you put the engine back together, did you degree the camshaft and confirm true piston Top Dead Center with the TDC marks on your timing cover tab/pointer and the balancer?

You mentioned that this engine has a Pertronix 3 distributor. Does this distributor use the Pertronix Ignitor III ignition module?
If so, I believe that Pretronix recommends a specific coil to be used with this module... the Flamethrower 3 coil with 0.32 primary resistance.
The Pertronix Ignitor III ignition module also has a built-in Rev Limiter... you may want to check that it is set correctly (or disabled).
Also confirm that you are running 12 volts to the distributor (and not using the stock resistance wire).

A couple other things to check would be a clogged/restrictive fuel line or fuel filter.... and low fuel pressure during acceleration.
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Old 7th-November-2019, 12:28 PM   #5
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yes that (and not using the stock resistance wire)screwed up my msd install for a while till we figured it out. an i'm using the blaster 3 coil. the fix was run a new wire with out the resistance in it.
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Old 7th-November-2019, 12:57 PM   #6
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Certainly sounds like a loss of volts or a crap distributor. Had this gappen msny times, even w those cheap curve kits.
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Old 7th-November-2019, 03:23 PM   #7
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Just a few thoughts. Unless the distributor is new double check to make sure the rotor button is good. Also check the cap especially if it has been sitting up. If this is a brand new build it is not uncommon to foul plugs when it first cranks. When building a engine the excess oil used on the cylinder walls and assembly lube can kill a plug. Spark plugs are fairly cheap so I try to keep a extra set on hand. I have had brand new ones just installed that caused problems. I recently had a coil wire cause me a problem. Id check that also. With it popping out of the exhaust it almost has to be a ignition/plug problem or something to do with a exhaust rocker.
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Old 7th-November-2019, 04:51 PM   #8
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Check for vacuum leaks.
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Old 8th-November-2019, 01:28 AM   #9
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One other question.
I just noticed you installed a retro-roller cam as part of the rebuild.
Did you also install a cam button with this set-up?... and correctly clearance the cam button to the inside of your timing cover?
I have read that roller cams installed into non-roller blocks (without the cam button) can cause the cam to walk forward... thus effecting your ignition timing.
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Old 8th-November-2019, 01:33 AM   #10
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Wow thanks for the replys. Had some time today for more checks but without a fix. Stuff i checked: cap/rotor cleaned terminals, fire order again, plugs look ok but rich. Next up ill confirm my wiring to the dist/coil and prob replace the dizt springs. Again symptoms,
Pops on acceleration above 3k and doesnt matter if from stop or cruise. Idles great and off idle is ok. And i am running an msd blaster coil but didnt seem to be an issue before. Ill check that limiter also on the petronix3 module
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Old 8th-November-2019, 01:47 AM   #11
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Also checked the valvetrain and readjusted the valves. First had them at 1/2 turn after zerolash, now at 3/4 turn. Called howards cams, they recommended one full turn. Thought that was a bit much
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Old 8th-November-2019, 04:12 PM   #12
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"3/4 turn on the valves", NO, too much preload. Use E-O, I-C method to set the valves, and only preload 1/4 turn, no tighter.

And "34 to 38" tells us NOTHING. What specs, please

INITIAL timing?
VACUUM ADVANCE degrees stop setting, and what type advance?
VACUUM ADVANCE source, full manifold, or ported?
MECHANICAL ADVANCE DEGREES?
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Old 9th-November-2019, 08:43 AM   #13
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Sounds like it might be a lean pop, might want to try richer jets.
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Old 9th-November-2019, 09:11 AM   #14
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Quote:
Originally Posted by Old Man View Post
"3/4 turn on the valves", NO, too much preload. Use E-O, I-C method to set the valves, and only preload 1/4 turn, no tighter.

And "34 to 38" tells us NOTHING. What specs, please

INITIAL timing?
VACUUM ADVANCE degrees stop setting, and what type advance?
VACUUM ADVANCE source, full manifold, or ported?
MECHANICAL ADVANCE DEGREES?
Yeap I have my buddies and any of mine at 1/4 to 1/2 preload on the build stand and forget them. I never go over them again. Timing for a good cam which I have no clue and never look at advertised duration only duration @.050" would be 18* initial and 18* mechanical is what I have my buddies 383 with Howards retroroller cam at.

If it's popping in the exhaust check your plugs and wires.
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Old 9th-November-2019, 03:08 PM   #15
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Are you sure the cam is installed properly? I was trying to tune an engine for a guy once where I could get it to idle at 500rpm and accelerate great till about 2800, then it would break up, sputter, backfire, etc. The cam was not installed correctly. It was like a 1/4 rotation out.
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