Carb & Exhaust Backfire at the same time

[tlorber]

Before pulling the dizzy, you might just swap the plug wires 180*. I had a mechanical dizzy in my '73 that ran fine. When I put the '82 electronic dizzy in I had horrible backfires out the rear and carbs. Car would not run. Keep in mind, there is only one way that the distributor will engage when installed. So I rotated the wires 180* out of phase and the car runs awesome.

Can't explain it just yet-I never took the time to see why the distributor is out of phase with the motor-but it is.

[FastWoman]

There's a slightly off-center notch on the linkage between the distributor and oil pump that supposedly ensures correct alignment, but I've read it's sometimes possible to turn the distributor 180 deg and still fit it into the notch. Maybe that's your situation.

One more thing for the OP to consider: The #1 plug might be lined up with the engine at TDC, but are the other 5 plugs in the right firing order from there? Maybe it's backwards? This is a common error.

Edited October 27, 2011 by FastWoman

[beermanpete]

Before pulling the dizzy, you might just swap the plug wires 180*. I had a mechanical dizzy in my '73 that ran fine. When I put the '82 electronic dizzy in I had horrible backfires out the rear and carbs. Car would not run. Keep in mind, there is only one way that the distributor will engage when installed. So I rotated the wires 180* out of phase and the car runs awesome.

Can't explain it just yet-I never took the time to see why the distributor is out of phase with the motor-but it is.

We have a similar issue with our '73. In the process of diagnosing a problem I had the distributor apart and back together a few times. Despite following the service manual explicitly the timing ended up 180 out. I put the plug wires in the cap 180 out to accommodate it and the car runs fine. The only consequence is that the plug wire routing is not as pretty.

As for the oil pump timing, I have not had mine apart but it seems it could be 180 out as well and cause the same problem.

[Ronaldo1973]

Am sorry for late response since my hand has stuck between the fan shroud and a running cooling fan of a 2500 HD sliverado truck ! :dead: thats why I love zcars more any way I have read all the comments here and am grateful to you guys

Its a timing problem almost for sure. You have convinced yourself some aspect of the time system must be ok, but it is not. Do not be afraid to challenge every detail of your assumptions.

I suggest you start from absolute square one with the timing. Really.

Remove the valve cover, remove the oil pump, remove the oil/distributor drive shaft. Put the engine at compression TDC, confirm with both #1 cam lobes "up" and look in spark plug hole for piston at top dead center.

Then re-assemble the oil pump/drive shaft lining up the marks on both. Notch on the side of the oil pump just below where the drive shaft enters, and a punch dot on the drive shaft. Put the pump back on the motor, straight in. It likes to go in a tooth off, might take a couple of tries.

Wish I could find a post that shows the correct position looking into the dist. mounting hole from above that shows the correct narrow/wide side of the drive tang relative to the the engine, I think its tang aligned to 11/5

Now put the distributor back in. Put the rotor back on (not the cap yet). Where is the rotor pointing? Better be forward toward the rad. The advance diaphram is pointing the same way. Look at the cap. The #1 tower is marked with a line cast into the cap. Put the cap on. That tower better line up EXACTLY with the rotor inside.

without removing the oil pump, i can confirm that the with cyl#1 @ TDC, the rotor and the advance diaphram are pointing toward the radiator, am sure about that since i have set cyl 1 @ TDC with valve cover off and the dizzy cap also off, and i varified that the rotor is pointing toward the rad while cyl # 1 @ TDC on compression

Now put the plug wires on, one at a time, remove them all from the cap, starting with #1. Go counter clockwise, 1-5-3-6-2-4 (not 153426!! Anyone who knows me knows that story....)

I will triple check this point again

There are many many posts here describing this proceedure in excruiating detail, do a little searching, you will find very descriptive pictures.

Report back what you have found. You will overcome this problem.

EVERYTHING that Kcars said! However, I'll just throw in a couple of other items:

Pull off your cap and rotor, and try rotating your distributor's breaker plate by hand. It should rotate smoothly, without binding, and it should be under spring tension. The mechanism often rusts and/or falls apart and gets stuck in some random position of advance. I doubt whether that could result in problems as extreme as you're describing, but it might be part of the overall picture -- quick to check.

Another part of the picture could be the valve lash. You say you tried adjusting it, but you couldn't get it right. To me that's a big red flag. WHY couldn't you get the valve lash right? (It's just an adjustment, after all.) Perhaps your valves are sticking? I'd suggest doing a compression test. You'll find out very quickly whether that's the case. Possible reasons for valves hanging are: They're bent. They're rusty. They're gooped up in varnish. You can address the latter problem with a solvent like SeaFoam, but the head might have to come off if it's either of the former two.

It's tempting to think of this as a single problem, but on an old car that's probably seen lots of neglect in its life, MULTIPLE problems are more typical.

I think i have also a bad valve lash problem, i will try to readjust them

compression is fine all cylinders have a compression between 130 and 145 psi cold

You don't need to take the pump or distributor out, and you don't even have to pull the valve cover if you don't feel like it. Pull the #1 plug out, disconnect the coil wire, put your thumb over the plug hole and stop when you feel the compression stroke (you'll feel it). Mark (or memorize) where the #1 plug wire is on the distributor cap and take it off. Look to see if the rotor is pointing there. If not, adjust the plug wires on the cap so it is, and make sure the firing order is correct.

If you're going to check valves, the valve cover will come off anyway which makes visual inspection of the cam the preferred option.

thank you guys I will keep you informed about it!

[FastWoman]

Ronaldo, when your crank is at TDC and your distributor is pointed towards #1, are your #1 cam lobes pointing up or down? Look through your oil filler hole with a flashlight to see.

Also, can you confirm that your firing order is not backwards? Crank the engine to see which way the distribor rotor rotates, and then confirm that the order from #1 is 153624 and not 142635.

[Ronaldo1973]

Ronaldo, when your crank is at TDC and your distributor is pointed towards #1, are your #1 cam lobes pointing up or down? Look through your oil filler hole with a flashlight to see.

Also, can you confirm that your firing order is not backwards? Crank the engine to see which way the distribor rotor rotates, and then confirm that the order from #1 is 153624 and not 142635.

Yup both lobes were pointing up (valve cover was removed) and the piston was at tdc when i looked through the plug hole and the rotor was pointing toward the radiator and perfectly lined up with dizzy cap tower # 1

I will triple check the firing order again with the cap off to confirm which way the rotor will rotate great hint

[FastWoman]

A trick to remember firing order:

15 is too young.

36 is too old.

24 is just right.

Or the 180 deg turned version for old folks like me:

62 is too old.

41 is too young.

53 is just right.

[5thhorsemann]

This is just a thought, but it could be the problem, I know it sounds stupid, but the stupid things are the ones that get missed every time. Here goes.

The SU bowel vents are plumed to the stock air box outside the air filter. Check the vent plumbing to be sure this is the case, if you are getting manifold vacuum to the bowls it will idle bad and do all kinds of funky things through the RPM band like backfire through the carbs, exhaust, stall and restart etc.

I know it sounds like an elementary mistake, because it is, but try just pulling the hoses off the bowels and see what happens, cant hurt, rite?

[Ronaldo1973]

Guys This is to report that the backfire has been solved, now when I crank the engine there is no backfire at all , and now I having fuel problem only (I think I can handle it)

I found a very stupid stupid stupid ( stupid up to the point I'd kill my self), I have the plug wires wired clockwise,

rewiring them corrected the problem

Thank you all guys specially Zkars and Fastwomen for there very detailed explanations