Intake Manifold Gasket replacement
#41
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.
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.
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.
#42
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.
What am I doing wrong?
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.
What am I doing wrong?
#43
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.
#44
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.
thanks will try this right now
#45
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
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
Last edited by nba1341; 11-02-2009 at 11:25 PM.
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4.6L (1996-2004 Modular) Mustang
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