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Vacuum or rich AFR can cause backfires, but typically they are out the exhaust.
When a backfire comes through the carb, what happens is the ignition fires before the intake valve is closed. I respectfully disagree with 1965screamer though. This means the timing is too advanced at idle. The iginition if firing before the cylinder is ready. If the timing was too retarded, the backfire would come out the exhaust because the ignition would be occurring while the exhaust valve is open. The solution is the same. You need to check and fix the timing. Get a timing light and turn the dizzy until at idle until you reach about 8*BTDC on the #1 cylinder. You will be in the ballpark then.
The first thing I would do is dead time it. To do this, rotate the engine over by hand until the #1 plug is at top dead center then check to see where your timing marks are. If your timing marks are 180* degrees away from the pointer, you are on the top dead center of the exhaust stroke. You will need to rotate the engine over until you are on top dead center of the compression stroke. Then check your timing marks. You should be close to the 0 mark on the balancer. If you are off by a little bit, rotate the engine until the pointer is at 0. Then pop the cap off the distributer and see where the rotor is pointing. It should be pointing directly at the #1 terminal. If it's not, turn the distributer until it is. If you can't turn it enough, you will have to lift it up out of the engine far enough to turn it a tooth one way or the other so that it does. After you have the rotor pointing at the #1 terminal, reinstall the cap and check your firing order one plug at a time. Keep in mind that your cylinders are numbered 1-4 down the passenger side and 5-8 down the driver side. If your firing order is correct. Start the car and turn the distributor to set your timing to the correct setting.
When you do time it with a timing light, be sure to remove the vacuum line from the vacuum advance on the distributer and plug the line. Once you have your timing set, put the line back on.
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Absolute rule number one: If it has tires or tits, your going to have trouble with it.
Ok i just hand turned the engine until my pointer was at 0 and my #1 cyclinder was at what i believed to be TDC, I used a metal rod and marked how far it went down each time and that was when it went down the least.
I then took out my distributor and reinstalled it pointing perfectly at the #1 port for my cap (my firing order is the 302 roller cam one). Put everything back together and I tried starting the car and just got backfiring out the carb and the car would not start at all.
If it is backfiring the carb with the timing set at TDC, something is not right. At 0* advance, your fuel charge should finish burning in your headers/exhaust. The engine should not be running real well and the exhaust pipes should be getting hot and pinging, but it should run. Take all the vacuum hoses off the carb and intake and cap them (do not leave a single port open) and see how it runs then. That will help eliminate vacuum leak issues.
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"Yeah, were runnin a little bit hot tonight. I can barely see the road from the heat comin' off of it." Van Halen
If it is backfiring the carb with the timing set at TDC, something is not right. At 0* advance, your fuel charge should finish burning in your headers/exhaust. The engine should not be running real well and the exhaust pipes should be getting hot and pinging, but it should run. Take all the vacuum hoses off the carb and intake and cap them (do not leave a single port open) and see how it runs then. That will help eliminate vacuum leak issues.
ok I set the timing to 10 degrees and its running just as it did before except its running rich like my nostrils were burning badly
before the gasket change the car was running very nicely i had recently lowered the jets on the carb and got it running perfectly
could the timing have been different before and now i need to adjust my carb accordingly?
I have not taken the car out to drive it yet I just got it to operating temperature and timed the thing btw so its been in the garage for 3 weeks
im kind of scared to take it for a drive any things to look out for as im driving it? signs of vaccum leaks or bad timing? at idle it is running very nicely just rich
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