BACKFIRE!!!

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BACKFIRE!!!

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BACKFIRE!!! - 3/30/2008 3:51:39 PM

SCHOON

Posts: 344
Joined: 9/8/2006
Status: offline

Took my 74 out for a ride today and when I gave it some gas it started to break up.
I thought maybe from sitting in storage for the past 4 months the gas was a liitle stale even though I added stabilizer before puting in storage.
I figured I would now take in on the freeway and clean it out.
Anyway, I stomped it and wound it up to about 4k and it sounded like it backfired through the carb.
I am still running the original point setup and the car was tuned 3k miles ago.

Thanks in advance for your suggestions.

Schoon

Post #: 1

RE: BACKFIRE!!! - 3/30/2008 5:46:40 PM

YANKEECORVETTE

Posts: 106
Joined: 12/16/2007
Status: offline

Sounds like you had a sticky valve in a head. If in the unlikely event that it happens again make sure you did not break a valve spring. P.S. go w/ a red ther is too many dark colored vettes out there.

(in reply to SCHOON)

Post #: 2

RE: BACKFIRE!!! - 3/31/2008 12:48:21 PM

Posts: 1066
Joined: 8/7/2006
Status: offline

Hi SCHOON, before you take the motor apart here's a few other things to check:
low float level
clogged fuel filter
low fuel pressure from pump
vacuum leak
incorrect timing, point gap or dwell
plug wires or too large a gap on spark plugs.
Also like YANKEECORVETTE says it could be a weak valve spring or a worn lobe on the cam but I'd check the easy stuff first. PG.

(in reply to YANKEECORVETTE)

Post #: 3

RE: BACKFIRE!!! - 3/31/2008 1:42:14 PM

SCHOON

Posts: 344
Joined: 9/8/2006
Status: offline

I hope it is something simple like a bad cap or points
I really don't feel like replacing the heads at this time.
PS
The car came from the factory in red. Someone went a little crazy with the present paint job.

(in reply to YANKEECORVETTE)

Post #: 4

RE: BACKFIRE!!! - 3/31/2008 1:44:21 PM

SCHOON

Posts: 344
Joined: 9/8/2006
Status: offline

Hi PG,
I willl let you know what the problem turns out to be.
I am leaning towards the cap or points.
It did feel like a stuck valve though.

(in reply to pg)

Post #: 5

RE: BACKFIRE!!! - 3/31/2008 2:08:01 PM

78buckshot

Posts: 671
Joined: 1/28/2007
From: Michigan
Status: offline

I agree with pg, go through all the normal tune-up stuff first, I'll bet it's ignition related.

(in reply to SCHOON)

Post #: 6

RE: BACKFIRE!!! - 3/31/2008 2:41:25 PM

Waxman

Posts: 1
Joined: 11/27/2007
Status: offline

Mine is doing something similar.

I have a Quadrajet and car seems to start fine and idle smooth.
When I step on it though the car will die, pop, and did backfire through the carb.
I was told that it was most likely an accelerator pump issue, clogged and or just not working right and needs attention/repair.

I have not confirmed this to be the problem but was told it was the most likely culprit and thought I woudl share.

NOT saying it can't be what others suggested as many many others have more engine knowledge than I do.

Good luck!

_____________________________

1972 Stingray
1975 Stingray
Body off Restoration
383 Stroker

Member/Founder of the Clara Driving Club

(in reply to 78buckshot)

Post #: 7

RE: BACKFIRE!!! - 3/31/2008 4:19:56 PM

78buckshot

Posts: 671
Joined: 1/28/2007
From: Michigan
Status: offline

So Waxman, when your engine is stone cold doe's it start with a couple of pumps of the peddle and then crank? If it's starting well and at gentle acceleration you have no issues then the accelerator pump is probably OK. You can do an easy check, with the engine not running remove the air cleaner, open the choke valve ( rectangle air valve about one inch by three inches), look down the throats of the primary venturies and move the accelerator, you should see a squirt of fuel down each venturi each time you move the accelerator. If you don't see fuel squirting then it's time for a carb. rebuild. A vacuum leak can cause similar symptoms.

(in reply to Waxman)

Post #: 8

RE: BACKFIRE!!! - 3/31/2008 9:25:33 PM

DryCreamer

Posts: 93
Joined: 1/28/2008
From: Muncie, IN
Status: offline

It's ironic there are 2 backfire posts one right after another, I have the same problem with my car. Just changes heads, intake, cam, and its a got a wicked part throttle backfire though my Eddy 750! I was driving around my friend Steve's neighborhood (who was gracious enough to let me use his garage for this 4 week process) with no hood and the car and it looks like a freight train puffin' around. Leaning towards a vacuum leak under the intake. I'm runnin' a Torker II, which I know won't pull the greatest vacuum, but I'm only suckin' 6" at idle, hopin' to at least get 12"+, and its an erractic idle, but it makes strong power 2500+ if I feather it through. Timing is solid, but backfires at part throttle detent whether its at 4 degrees advance or 18. I've just been him-hawin' around because I don't want to pull the intake back off. So back to the grind. I think those cheap fel-pro KS2600 kit intake gaskets just didn't seal right so I picked up some wide Mr. Gasket ones, unless my intake is warped, because it is used, but darn it, nothin' else will fit under the hood of these cars!

_____________________________

Clayton

(in reply to SCHOON)

Post #: 9

RE: BACKFIRE!!! - 3/31/2008 9:36:13 PM

Rich G.

Posts: 109
Joined: 1/12/2007
Status: offline

If it ran good when you parked it I'd run it for a while and use up most of the gas in it and then run some fresh gas and see what happens. Might just have to get the juices flowing again. I took my Harley out for the first time this year and it was popping and running like crap till I got some fresh gas in it.

(in reply to DryCreamer)

Post #: 10