Chevy Nova Forum banner

1 - 20 of 44 Posts

·
Registered
Joined
·
80 Posts
Discussion Starter #1
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
 

·
Registered
Joined
·
1,177 Posts
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.
 

·
Registered
Joined
·
2,467 Posts
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.
 

·
Registered
Joined
·
172 Posts
Certainly sounds like a loss of volts or a crap distributor. Had this gappen msny times, even w those cheap curve kits.
 

·
Registered
Joined
·
752 Posts
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.
 

·
Registered
Joined
·
1,177 Posts
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.
 

·
Registered
Joined
·
80 Posts
Discussion Starter #10 (Edited)
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
 

·
Registered
Joined
·
20 Posts
"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?
 

·
Registered
Joined
·
20,088 Posts
"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.
 

·
Premium Member
Joined
·
2,095 Posts
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.
 

·
Registered
Joined
·
80 Posts
Discussion Starter #16
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.
ya, im running that cloys quickbutton timing cover with adjustable button.
 

·
Registered
Joined
·
80 Posts
Discussion Starter #17
Changed up some things gave me alot more bottom end torque for some reason. But still has that minor pop. Replaced my coil to a Petronix3 coil to go with the dist and replaced the dist cap. This pop occurs on vary fast/hard kicks of the throttle. If i give it a medium to slow throttle wrap it sounds great. And the issue sounds only in upper rpms 4500. Otherwise no pops down low, starts great, no smoke, not noticeable at constant cruise speed either. I feel like its when the secondaries kick in. This is a 750hp carb.
 

·
Registered
Joined
·
80 Posts
Discussion Starter #18
"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?
old man, some spec sir. Ya the intel from Howards cams to use one full turn after zero lash sounds alot to me. Im at 3/4 now but may go down to 1/4. As for the timing. Initial is around 18, mechanical limited to 16 all in before 2600rpm. As for vacuum adv. Ive tried both with and without plugged into the full manifold port on the bottom of the holley 750dp. My distributors vac adv is not adjustable either. might change out the mech adv limiter to 20 try that.
 

·
Registered
Joined
·
417 Posts
When you made the cam upgrade to a hydraulic roller, did you change the valve springs? If the original cam was flat tappet, there's a possibility that you don't have enough valve spring to handle the faster ramps of the hydraulic roller. I would consult the cam manufacturer as to spring requirements for the new cam.
 

·
Registered
Joined
·
1,177 Posts
Changed up some things gave me a lot more bottom end torque for some reason.
Glad to hear that you have made some progress. What did you change?

This pop occurs on vary fast/hard kicks of the throttle. If i give it a medium to slow throttle wrap it sounds great. And the issue sounds only in upper rpms 4500. Otherwise no pops down low, starts great, no smoke, not noticeable at constant cruise speed either.
*Does the pop/backfire occur while you are driving?... or just in Park and while you are revving your engine (as described above)?
*Does the engine still hesitate when it starts to pop/backfire out of the exhaust?
*Do you know what size primary and secondary accelerator squirters you have installed on your Holley 750dp?
You primary and/or secondary accelerator squirters may be too large and squirting too much fuel into the carb during very fast/hard kicks of the throttle... thus causing a hesitation and/or backfire due to a brief "over rich" condition and un-burned gas reaching the muffler where it then explodes/pops.

One other thing... Are you using "Open Chamber" mufflers? I have read that open chamber mufflers do not silence exhaust backfires as much as other types of mufflers.
 
1 - 20 of 44 Posts
Top