When I start up my car it back fires through the carb. I just went through the top half of the motor, [all new] it does not do it all the time. Any suggestions ! [It's a 396/375hp all stock]

1)Does it have a choke that works?
2)I'd check the spark plug wiring/firing order very carefully. Ditto for the timing/dwell.

Tom

Backfire though the carb = Distributor is 180 degrees off. Pull your distributor and rotate it 180, you'll be fine.

The distributor doesn't have to be off 180 to backfire through the carb, I had mine retarded 30 at idle and it backfired through the carb. Backfiring through the carb mean that a intake valve or valves are open when the plug is firing. Unless the cam timing is way off it is usually caused by ingntion timing.

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JT
71 SS 350 soon to be 454

Luke, as they say it's the timing, their right on. Also if you have points/condensor, a bad condensor/points will cause the same back fire. I was there last year with a 396/375 when his Pertronix died and I installed a good set of used points and a brand spanking new condensor. Well he ended up towing it to a buddies garage at Speedy Muffler and they swapped the points and condensor and away she went. Problem solved. Never in my 45 years I've seen a bad condensor do such a thing.

Mark

[This message has been edited by COPO (edited 05-02-99).]

Thanks for the help!

99 times out of 100 when an intake is pulled, or top end work is done, where the distrubutor is pulled out and reinstalled, if the thing backfires through the carb, the dist was put in 180 off. At any rate, hope you figure it out.

When I changed cams in my 350 we thought we had it off 180. I had only worked with Fords upto that point and on the Ford you put the gears dot to dot and the dist. at cyl. 1. So I thought I had it 180 and tried it and it still backfired. Like I said before it was 30 off.

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JT
71 SS 350 soon to be 454

Before you change it 180 degrees take the driver's side rocker arm cover off and rotate the engine to what you think is the compression stroke. Now if both valves are closed when you close in on top dead center you have it correct and the timing is just probably off quite a bit.

But if the exhaust valve is open the others here are correct it is 180 degrees out - you are firing the number 1 cylnder on the exhaust stroke. The reason so many have said that is the problem is because we have all been there, done that, and got the T-shirt!

I still smile when I think of the last time I did it - nice big flames coming out of the carburetor.

John

Mine was timing. I had it 4 degrees retarded instead of 4 degrees advanced. It would back fire through the carb when you punched it.

Like John said, put the number one cylinder at Top Dead Center. You do this by putting your finger over the spark hole and turning the engine slowly (w/wrench) until your finger is blown out. The timing mark should be at zero.

When you set your timing make sure the idle is at the speed it should be. My spec was 4 degrees advanced at 500 rpm. 500 is really slow! Until I got it down there, I never got the timing right.

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Jameel Qazi
#'s 67 SS

timing's off for sure!

in my opinion the easiest way to check for TDC after the compression stroke is remove the #1 plug and have a buddy crank the motor (coil disconnected) just for a microsecond while your finger is covering the spark plug hole then your finger will make a farting noise and then take it from there with a wrench on the crank pulley main bolt, watch the TDC mark on the balancer.

then install the distributor, rotor pointing to the #1 plug wire on the cap

Farting noise?????Then I'm always on TDC!!!!
http://www.chevelles.com/forum/wink.gif

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John 67SS
ACES #2887

[This message has been edited by 67ss (edited 05-03-99).]

You might also want to re-check your valve adjustment. I have seen that cause it too. Good luck.