Backfiring symptoms.

[Fernando Mendes]

As a general rule,backfiring INTO THE MUFFLER indicates TOO RICH a fuel mixture.Backfiring INTO THE CARBURETER indicates TOO LEAN a mixture.Make necessary adjustments at carbureter.STICKING VALVES or WEAK VALVE SPRINGS will also cause backfiring.Extremely LATE IGNITION TIMING will cause backfiring.

[John-T-53]

I had a sticking intake valve in my Chevy 283 that caused a LOUD backfire (or front fire) through the carb.This occurred out of nowhere, cruising down the freeway at 65. I almost sh*t my drawers!

The engine had previously got hotter than normal sitting in traffic and I think caused the oil to break down. An oil change solved the problem.

[TodFitch]

From experience I will add that a leaky exhaust manifold will cause backfiring into the exhaust especially on deceleration or using engine braking on a grade. That might have been exacerbated by a bit of a rich idle setting on the carburetor, but the problem was fixed by getting the manifold mating surface to the block machined flat so the gaskets could actually do their job.

[Mark D]

I took the wife out for an ice cream run in Ruby last night. First run since the new head gasket was installed. After running her up to temp, I drove about two miles and slowed to take a left turn, then I down shifted to 2nd and took the turn. After the corner I applied gas and KA-BANG!!! Ruby let out a backfire from the muffler which shot the chrome muffler tip into the middle of the street behind us. Scared the dickens out of the wife (made me chuckle) and I quickly pulled over to retrieve the newly missing chrome tip.

Shortly after that I noticed that she was missing every now and again so I stopped and quickly checked under the hood. Idle was fine and all check ed out OK, so off we went for icecream. 8 miles down the road I stopped and parked the car, after we where done I tried to start her and she had plenty of starter motor, but no catch. I figured it might be flooded so I let her sit for a few minutes but alas she still wouldn't catch. So I checked for spark and found nothing at the plugs which lead me to find a loose connection from the coil at the dizzy cap.

Thats all it took and she started immediately. I'm wondering if this wire was the fault for my back fire? Seems unlikely, but I could imagine gas vapor building up in the exhaust and when she caught it ignited causing the very very loud response.

Keep in mind I made no changes to the carb but did remove and clean the dizzy, but did re-time the engine after that. I am weak at best in diagnosing dwell, but think this may also be part of my issue.

Thoughts?

Edited April 4, 2012 by My48Ruby

[HanksB3B]

My48Ruby,

That's a funny story. You guy's don't wait much longer than the snow melt to out for ice cream do you. After I rebuilt my truck and got everyting as good as I could, I took my truck to a local shop to a guy that has a renowned reputation of being "the best".

The shop ran diagnostics that I have no equipment for checked and adjusted and fine tuned the fuel and ignition system. He also noticed that I had used Packard 440 suppression spark plug wires and recommended as soon as I could to change them to solid core non-suppression wires which I did whithin a week. My truck ran beautifully as soon as I left the shop I could really feel the difference. Power and acceleration felt much smoother and much stronger.

For me a marginal mechanic (not a motor head) it was a way of checking my work and the work of others during the rebuild process. An extra $125 that I did not regret spending.

Hank

[Mark D]

Your suggestion is a good one Hank. I've got a local mechanic that I really trust but with my schedule I have'nt had the time to get a visit coordinated. The spark plug wires I used where off the shelf cut-to-length from Tractor Supply. I had installed oem cloth covered versions on there last year, but didn't like the fact that I was getting mildly shocked through the cloth covering and with the engine looking so fresh I figured the $20 was a decent investment. I removed the factory molded boots with a knife and re-installed my ever-dry boots. The 90 degree plug-clips on the new wires where superior from the ones supplied with the everdry kit and the dizzy connection ends where a much more solid connection as well. I guess I just didn't seat the dizzy end of the coil wire well enough.

[HanksB3B]

That's a really great price and a good looking set of wires from Tractor Supply. Do you know if they are non-suppression? Jeff Balazs had inquired about the Ever-Dry kit and although I like them and would consider using them, other than when I give the engine a light wash I think other than for looks they wouldn't do me much good. I forget they are pricy too are the Ever Dry caps available without the wiring (if you say you did not really like them due to the shock factor). I no longer feel I have a need for Shock Treatments like I did in my youth, when just for fun we'd grab on to a lawnmower spark plug, or touch 9V batteries to our toungue.

Hank

[Fernando Mendes]

Ignition system-75%

For "NO SPARK" and "WEAK SPARK" cases.

Fuel system-25%

For "GOOD SPARK" case only.

When test indicates a good spark is occurring at each spark plug,the ignition system may be eliminated and the fuel system should be checked.

Engine misfires-continuous misfiring in one or more cylinders

*Faulty spark plugs are a frequent cause of engine misfiring-check the following:

1.Is recommended type plug being used?

2.Clean and readjust spark plugs.

3.Inspect porcelain at lower end

A.If porcelain is very WHITE-plug is too HOT-Use COLDER plug.

B.If porcelain is LIGHT BROWN-plug is CORRECT-Replace with same type.

C.If porcelain is BLACK or OILY-plug is too COLD-Use HOTTER plug.

*If the possibility of faulty plugs has been eliminated proceed to check the following:

1.High tension wires may be leaking.

2.Distributor cap may be defective.

3.Cylinder may have insufficient or uneven compression.

[Mark D]

Stopped at the garage on the way home from work. Just couldn't let go of this another night. Traced my steps in the rebuild process, traced the wires I touched and found nothing. Pulled the cap off the dizzy and found that the flat copper strap that rides the back of the spring had split! Barely visible from the angle I was looking from but it caught my eye. So I pulled the dizzy and then pulled the guts and managed to tuck the strap under the screw. Reinstalled it all and she fired on the first push! Love it when I solve these things myself. When I got home to the mailbox I found that my new NOS distributor breaker plate assembly (ebay) had arrived in the mail! Someone is looking over my shoulder. Tomorrow is another day and the weather is supposed to be great.

[Fernando Mendes]

Love it when I solve these things myself.

[Mark D]

Little update to offer. Went out in the car last night for a quick run, something didnt sound right from the exhaust. Crawled under the car to find my new oval muffler now had a distinct round shape in the middle. I am very impressed that it stayed on the car considering the deformation.

It must've blown the baffles in the interior of the muffler cause the rattle sound is definitely coming from the insides. I'm a little peaved that this muffler has been on the car for less than 300 miles, but the rattle is driving me nuts, so I guess I'm gonna have to find a replacement.

I think I'll look at a straight thrush glasspack or a cherry bomb this time, they're only $30 on ebay. I'd like to step up the audible rumble a bit.

[Fernando Mendes]

My48Ruby,you have the same style of poet like me.I like too write all the happenings that occurs with my three trucks.We live with more emotion.My wife hates them.Please send a picture of your truck.

[HanksB3B]

Fernando, dile que mejor que empiece a gustar sus camiones o enviaré Gabriella para hablar con ella sobre eso.

A ella le gustaba mi camión,

Hank

[Fernando Mendes]

O que é que é isto meu irmão?!

[Mark D]

Non hai camión na miña garaxe, pero só un coche. A miña muller non permitiría que un camión con tales curvas.

[Dave72dt]

I think I need to paint my truck green. Obviously a color that attracts pretty women. Some kind of a 50's- 60's gathering or just a day at the beach?

[Fernando Mendes]

Tow wrecker saving a girl.