View Full Version : dynamite sounding explosions coming from exhaust


SulphurDave
02-03-2006, 06:08 PM
Here lately when I go to crank up the Nova it has been getting harder and harder to start (giving it more gas and more cranking tries than usual) but when it did fire up it would take the normal "warming up" to get a good lopey idle. But the last couple of times trying to start it the idle sounds terrible like it barely wants to idle. Keep in mind I haven't adjusted anything since I've had the car now for a few months and when I got it it ran fine. Well today again it took a longer than normal amount of time to crank it and when it did run (barely idleing) I would get these loud as almost dynamite explosions occasionally out of the exhaust. So loud it hurts your ears and then I just turn it off. I'm just getting into this and have no idea how to tune a carb so yea I plead dumb on my part. But what exactly is happening here? Here's the specs on the motor:

383ci sb
4 Bolt Main
Forged Alum Flat Top Pistons
Forged 5.7 Rods
Lunati Hydraulic Cam 246 Duration / 520 Lift
Camel Hump Heads
Comp Cams Valve Locks, retainers, springs, etc.
Stainless steel valves
Victor Jr. Intake Manifold w/ Air Gap
Holley 750 Double Pumper Carburator w/ 2" Spacer
Double Roller Timing Chain
Mallory fuel filter canister type w/ replaceable filter
Jegs Pro Starter 4.41:1 gear reduction 1.9HP w/ Push Button Start
MSD Pro Billet Distributor
MSD 6AL Ignition
MSD Blaster 3 Coil
MSD Adjustable Timing Control
MSD 8.5mm Super Conductor Plug Wires
Hedman Headers 1 3/4" Primaries to 2 1/2" Pipes w/ Flowmaster Mufflers

Strokinit383
02-03-2006, 07:28 PM
It sounds like your timing is off. Is your distributor hold down loose?

SulphurDave
02-03-2006, 09:07 PM
It sounds like your timing is off. Is your distributor hold down loose?

everything on the dist. is on tight plus it's never been messed with. however i do have a msd adjustable timing control knob inside the cab that's always been set on 7 and goes to 10. it's been played with a little but it always goes back to 7 when i'm done. although i never heard a difference in the motor before while turning the knob.

Strokinit383
02-04-2006, 11:18 AM
Sounds to me like its firing too late. Try advancing the timing a little.

SulphurDave
02-04-2006, 06:56 PM
Sounds to me like its firing too late. Try advancing the timing a little.

would that be an adjustment from the adjustable timing knob or do i need to advance the distributor? what am i suppose to hear while the motor is running when i adjust the timing control knob? because when i tinkered with it before i never heard a difference.

Strokinit383
02-04-2006, 08:26 PM
Im not quite sure how those timing knobs work. I would try it there 1st since it so easy to do. Maybe write a small mark on your distributor base and intake manifold as a reference to where you started. That way when you try advancing it if it doesnt work youll know where to go back to.

bowtie notch
02-05-2006, 08:54 AM
bad plug or wire?

SulphurDave
02-05-2006, 12:09 PM
bad plug or wire?

i just changed the plugs to some champion race plugs a couple months ago. but the car has never been driven. it has just been sitting in my driveway and i crank it up every now and then. i do remember when i first put the plugs in it cranked up really easy and it has progressively gotten harder to start since then. and then now it started doing the backfires and barely idleing. i just don't understand because nothing has been messed with i mean the car just sits there.

CarelessAndImprudent
02-05-2006, 03:41 PM
I'd check to make sure your wires are arcing for any reason. I'd pull the distributor and get your timing in the general vicinity by finding top dead center, then installing your distributor per directions I'm sure you can find somewhere on the net. You could always check your timing with a light, but that can go bust if you have a different style balancer then was marked for your engine.

I'd for sure pull the adjustable timing knob though, sounds like more trouble then it's worth.

Definitely a timing problem though, cause mine did the same thing when I installed a new distributor. Turns out it's got a new balancer on it, with the wrong timing marks.

SulphurDave
02-06-2006, 12:04 AM
I'd check to make sure your wires are arcing for any reason. I'd pull the distributor and get your timing in the general vicinity by finding top dead center, then installing your distributor per directions I'm sure you can find somewhere on the net. You could always check your timing with a light, but that can go bust if you have a different style balancer then was marked for your engine.

I'd for sure pull the adjustable timing knob though, sounds like more trouble then it's worth.

Definitely a timing problem though, cause mine did the same thing when I installed a new distributor. Turns out it's got a new balancer on it, with the wrong timing marks.

not saying the timing thing is wrong but why would it all of a sudden just start acting up like that when it only gets started once or twice a week and never driven? it doesn't make sense. it ran so perfect when i first got it... real responsive fast revving up and down. it would rev down just as fast as it would rev up. perfect idle. so it wouldn't be a carb problem? for sure a timing problem? once i do figure out what the problem is i'll be sure to post it on here.

SulphurDave
02-06-2006, 06:59 PM
Sounds to me like its firing too late. Try advancing the timing a little.

Definitely a timing problem though, cause mine did the same thing when I installed a new distributor. Turns out it's got a new balancer on it, with the wrong timing marks.

points for you guys. it was definately a timing problem. i advanced the dist. a few degrees and tweaked the air/fuel adjustments and she lined right out. now it runs the way it did before. one of my buddy's (who has a 10 sec monte carlo) suggested i reduce the jet size on the carb though. it still has a little smoke out of the exhaust and has always done that. i know that 750 double pumper is dumping some juice so i might jet it down and see what it does then.

Strokinit383
02-07-2006, 11:20 AM
Glad to hear its back running correctly.

SulphurDave
02-27-2006, 12:34 AM
Glad to hear its back running correctly.

Yea for a week or so. I've had to recharge the battery a couple times from it turning over so much and not starting. When it does start it runs fine. Well I did have that issue where it was backfireing incredibly loud so I advance the dist. some and cured that. But it gets to the point to where I have to change the plugs every couple months or so because they get fouled. I don't drive the car it just sits in my driveway and I crank it up every week or so. I had it running fine last weekend and then today I go to crank it and it starts doing it all over again just turning over and over and barely hiccuping like it wants to start. Also today it started making a new noise while trying to start. While it's turning over occasionally I get these loud metal on metal grinding noise from the motor and gas spurts up out the carb and the starter stops for a second then starts again all while never letting up off the push button starter. It sounds like the motor internally is where it's coming from but it's hard to tell. Any clue where to start looking for the problem? Starter maybe? It's the Jegs Pro Starter 4.41:1 gear reduction 1.9HP. Carb issue maybe? I was once told it needs to be jetted down some but I haven't fooled with that yet. But that wouldn't be why it's making that louding pop/grind noise while turning over. It used to run so great and start fairly easy and now it's not and it never gets driven. I don't understand.

Strokinit383
02-28-2006, 06:57 AM
If its shooting gas and air up out of the carb, it now has a little too much advance. Try retarding it by spinning the distributor about 1/4" or less counter clockwise. See if that fixes it.

CarelessAndImprudent
02-28-2006, 03:59 PM
Sounds like you may want to go ahead and redo the timing completely to see if that fixes all your problems. Put it at top dead center and set your distributor per its directions and then start it and put a light on it.

The 750 dp does sound a bit big, but it shouldn't be causing your problems

CharlieCobra03
03-01-2006, 03:13 PM
Take it to yer local dyno and do a run with a sniffer in. Get the timing right, get the A/F right and find out what it's putting down all in one trip.

SulphurDave
03-01-2006, 10:00 PM
If its shooting gas and air up out of the carb, it now has a little too much advance. Try retarding it by spinning the distributor about 1/4" or less counter clockwise. See if that fixes it.

I might have to try that.


The 750 dp does sound a bit big, but it shouldn't be causing your problems

yea but can it just be jetted down some and keep the carb.. that's my main wonder with the carb.

Take it to yer local dyno and do a run with a sniffer in. Get the timing right, get the A/F right and find out what it's putting down all in one trip.

I'll let you take a look at the car and you'll see why I can't do that.

http://img.photobucket.com/albums/v113/ElectronGS-R/1972%20Chevy%20Nova/FrontSide1.jpg

http://img.photobucket.com/albums/v113/ElectronGS-R/1972%20Chevy%20Nova/Rear.jpg

CharlieCobra03
03-02-2006, 12:19 PM
What? It'll still work on a Dyno. Might be tough if the polizie see ya driving there though. Nothing a bigger hammer wouldn't fix.

CarelessAndImprudent
03-03-2006, 12:00 AM
Looks like you should build the first convertible nova!

SulphurDave
03-03-2006, 06:51 PM
If its shooting gas and air up out of the carb, it now has a little too much advance. Try retarding it by spinning the distributor about 1/4" or less counter clockwise. See if that fixes it.

i did and then went to turn on my ignition, full pump etc.. and i had nothing. no juice. my dome light and small things come on but nothing else. no fuel pump, ignition, dash lights, electric fan... nothing. it's funny how i dont touch the car for a week and things keep breaking. if it ain't one thing it's another.

Strokinit383
03-04-2006, 12:47 AM
Is your fuel pump mechanical or electrical? Do those old novas have something like a starter enable relay? Battery low? Bad grounds? Bad starter solenoid? Loose connections? Corroded connections? Broken wires from the ignition? Just some ideas off of the top of my head. Give me a couple more symptoms and we can narrow it down.

SulphurDave
03-04-2006, 10:41 AM
Is your fuel pump mechanical or electrical? Do those old novas have something like a starter enable relay? Battery low? Bad grounds? Bad starter solenoid? Loose connections? Corroded connections? Broken wires from the ignition? Just some ideas off of the top of my head. Give me a couple more symptoms and we can narrow it down.

It's a Holley Black electrical fuel pump, The car is all rewired with painless wiring although I see a lot of cut wires (was like that when I got it and ran perfect) so it's hard to tell what's coming and going, the battery that was in it was supposed to be fully charged. I had it on a trickle charger a few days ago because I ran down the battery turning over the motor so much that day. I even swapped out the battery with the one out of my old RX-7 and still nothing. I was under the dash checking fuses yesterday. It has the old style glass tube-like fuses under the dash along with some up-to-date fuses I'm guessing because of all the MSD stuff under the dash. The starter is brand new so it better not be bad, I fiddled with some connections and jiggled some wires around with the fuel pump on to see if I had a loose connection and I didn't find anything. And nothing looks corroded. I almost don't wanna fool with it anymore until I take everything out of the Nova and swap it over to my truck when I get it back. That way I can just start fresh. I just wanted to crank it up every now and then until all of that took place. I bought the car knowing I was taking everything out so I'm not tremendously upset.

rapid_rat
03-04-2006, 08:44 PM
When I opened up the exaust on my car it popped and banged through the exaust due to a lean condition. Also, when a car sits but gets started on occasion but not "driven" it can cause plugs to foul up even if there new. You have to bring the motor up to temp n decent rpm so the crap gets burned off and does'nt settle on them. I've had that happen a few times. That also caused popping out the exaust, and it got harder and harder to start everytime I did till it finally would not start. Soon as I put fresh plugs, bam. Ran perfect again.The old ones seem to act up more as far as the little things go when there not driven that often. Mines an 80 and shes turning into an old b***h.

SulphurDave
03-21-2006, 11:01 AM
Sounds silly but the whole time it was my power safety switch on the back of the car. It didn't have a good connection apparently because I rewired it and I had juice after that. Shockingly it didn't take much for it to crank either. I took some timing back out of it and it ran great. I wonder what will happen next week when I crank it up. I should have my truck out of the paint booth by next week so I'll be taking the motor out anyway and putting it in the truck.