Gents !
Need some input from lots !
I'll try to explain best I can.

Recently purchased 1980 vette.
1000 miles on GM crate engine from Summit USA 350 HO
Holley 600 Carb and hedders

Vehicle just brought over from Georgia to Canada Ottawa !
Guess its the first time she sees the white stuff

The transport guys had a hard time getting it rolling. They "flooded" the engine repeatedely because there's no choke on the carb. Nice weather in Georgia didn't require the choke I guess....
I had a hard time gettin' it started here in my heated garage.
We finally checked the plugs and what a nasty surprise
Those plugs must of been from the original engine and transfered into the new block ! To make the matter bit worst, among the 8 of them, there was AC Delco regular ones and some others were platinum brands...
I'm sure that didn't help.
When I took the plugs out, some were WET soaked, other were cooked and it was obvious NEW PLUGS were NEEDED BAD !

Well I got the recommended NEW plugs and checked the gap and VROOM !!!!

Now here's the problem ...
Once warmed up(15min) idling, I accelarate fairly hard(stationary / approx 3000rpm) and when letting go of the pedals, the right bank/muffler backfires
Then the engine idles perfectly 700-900rpm...

Since the vehicle was FLOODED repeatedely, is it possible that it created carbon or accumulated fuel in the Hedders causing backfires ?
There's 5ft of snow down here mixed with salt. No way I'm taking it out for a drive

Any input anyone ?

Phil

 

Back firing in the exhaust is generally a lean condition. Make sure the ignition is setup correctly. Maybe open up on the idle mixture a bit. Check for vacuum leaks.

BigBlockk

Later.....

 

Tks BigBlock !

What do you mean by the ignition setup ?
Where do I start when you say checkin' for vacum leaks ?

Just a beginner mecanically inclined. Not much experience but can handle it with a good friendly neighbour checking over my shoulder !

Phil

 

Check timing. You will need a timing light..

With the motor running check all of the vaccum lines comming off the carb. You might be able to hear a vaccum leak, Like an air leak.

Tuning is going to be hard if you dont have a bunch of experience with it.. Do some searches on the forum. Tuning, timing, carb setup, vaccum leaks...

 

might need to adjust the carb for the higer altitude of canada. email lars on here he the best

 

a small exhaust leak causes backfiring.
to even it up, drill a small hole in the other side Boom BOOM! i think it sounds
But i plugged the leaks as the cops started following me around

 

First, just to clarify the terminology:

"Backfiring" is a pop/explosion up through the carb.
"Afterfiring" is a pop/explosion out the exhaust.

If you are getting afterfiring when you let up on the accelerator, you are running lean on the transition and idle circuit. You can do one of several things or a combination of the following:

Make sure the carb is correctly jetted for its carb number and that the floats are set right. If the carb is to its spec, bump primary jet sizes up 2 sizes.

Check idle mixture screw settings and make sure the two sides are equal. If they're less than 1 turn out from seated, start with a 1-turn setting and tune for best idle from there. If it still afterfires, richen them up 1/4 turn.

Make sure your primary and secondary idle speeds are balanced - you should have the same idle throttle opening on the secondary side as the primary side.

Make sure your vacuum advance is functional and hooked up to manifold vacuum (not the ported source on the carb). The lean-out caused by slamming the throttle closed needs an early spark to ensure combustion.

 

This poster wants advice on what could be causing his backfiring issue and your advice is to drill a hole in his exhaust pipe? Ruining his exhaust system isn't going to solve his problem. The advice from some of the other posters is sound though. I would guess a minor tuning issue, either timing, advance rate, A/F ratio or carb could just be a little lean from altitude change or lack of a choke in your colder climate.

 

you took the bait! what a moron u r today i hope tomorrow will restore your sense of humor.

too bad, but gave me the best laugh in a long time
I NEVER WOULD HAVE PICKED YOU! what a surprise

a clever retort would be:
and what goes in the hole?
answer: oxygen sensor
DUH!

I'm not getting paid for this, so i may as well get a laugh now and then. I bet the OP is smart enough to check for an exaust leak, and fix it if there is one.
There are other possible causes, but i'd rather get the ideas flowing, and let others do the typing.
This works very well.

 

You have some nerve calling me a moron. Some of your posts on the 4 hole spacer such as running your PCV off a single port would cause a serious lean condition on a cylinder and possible detonation or complete engine destruction. You claim to be a tuning guru and dole out advice on more than one occassion that could have devastating consequences to someone's motor that chooses to follow your poor advice. Then you make an idiotic response to a real problem and call me a moron. If you are truly such a tuning guru why not offer something constructive to the post instead of belittling the people that try to help that really do have a clue.
True you are not getting paid for this and your warped sense of humor would sometimes cause severe problems for some that would foolishly take your advice. There are a lot of people that post here looking for guidance that have no or very little mechanical experience that want to learn and want constructive helpful advice not ridicule and posts who's sole purpose is your personal entertainment.
The advise Lars has provided is exactly what this poster needed to hear. He is a true tuning Guru, a big help to a lot of our members and a valued asset to the forum. And he is not getting paid for this either.

 

Boys.... boys..... boys. Let's be nice. Can't we all just....get along?

To the poster: You might want to buy a vacuum gauge at your local auto parts store. It is a necessary device for diagnosing vacuum leaks, setting up carb idle, and solving problems with vacuum operated equipment (headlights, wiper door, etc.). Also, you want to resolve any vacuum issues before you try to finalize idle adjustments.

 

very funny!
my hats off to you; u r funny!

 

would the moderators please chime in?
is my short story both a little amusing and thought provoking, maybe even a little instructional? Would a sane person run out and drill a hole in the exhaust?

 

Thanks to everyone !
Will print the answers and use them step by step !

No I won't drill the new muffler system !

63MAKO I salute you !

As for Matt, maybe your intentions were to have fun but you should be carefull.

THANKS AGAIN !
Phil

 

By any chance did you doublecheck the plug wires since it started backfiring after you changed the plugs? Even if you did them one at a time they still could be out of order from the previous owner.
Mike

 

I have a 65 that I bought to sell and it has a GM 350 HO crate that came complete with a 600 holley. The car was poping through the carb when it was cold and poping through the drivers side exaust when warm. When I pulled the plugs I had exactly the same thing as you described. Front plugs were dry and the back ones were gas fouled. I suspected a power valve in the carb so I put a kit in that, replaced all of the plugs and set the timing. Engine runs perfectly now.

 

examining the facts here would suggest that the explosion in the tail or exhaust pipe is from the fuel pumped into the engine while someone was trying to transport the car and later when the same problem existed until the fresh set of plugs allowed it to start. But raw fuel in the exhaust exploded or whatever the appropriate politically correct phrase is used in to days charged atmosphere so as not to hurt anyone's feelings. What happened really happened? the SOB backfired in the exhaust from excessive fuel in the pipes.


Hes lucky the muffler didn't blow out too.....i`ll raise a brimming glass of cheer if no one else cares

 

if so it should clear up real fast

if they put old plugs in it what else old did they put on that crate?
ie. how does the carb, intake, wires and distributer look?

1000 miles every thing should look new

 

I don't think Canada as a whole is considered a higher altitude. Latitude yes...altitude no.