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Discussion Starter · #1 ·
sometimes when i get up in speed say 65 70mph and let off the gas the car backfires it does it at the track kinda bad. Is this the timing? how hard is it to do yourself? thanks :dunce:
 

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Is it backfiring out the carb or the exhaust? What is the rule of thumb with backfires let see if I can remember... Out the carb is timing and out the exhaust is fuel ,something along those lines... Anyhow timing your car is very easy. Do you have a timing light? If not go grab a decent inductive timing light from Sears or your local parts store crawl under your 'stang and see if there are any marks on the harmonic balancer next to some numbers. That should be your setting go fire your engine up ,hook up your timing light loosen the distributor hold down bolt ,pull the vacuum line going into the side of your distributor ,plug it and aim your timing light down to the harmonic balancer. You should see a little pointer aiming towards the balancer align that mark with that pointer by turning the distributor clockwise to advance the timing or counter-clockwise to retard the timing once those two align you are timed! Well to factory specs at least... Should be somewhere around 8 degrees... Hope those directions were decent enough for you to understand I am not the best at giving directions but I try to help. Oh before I forget regarding your timing do you know if the cam has EVER been out of that motor could be some issues regarding that. Let me know if this helps any! :cool:


Keep the wheels spinnin' and the beavers grinnin' i'm out. :cool:
 

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Discussion Starter · #3 ·
thank you

as far as i know the cam hasent been out. and it back fires out of the exhaust. you said the carb might be to big remeber 650 holley could that be why?

thanks
 

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It could be your carb issue but I have another question. Are the distributor wires routed to the correct firing order for the engine? Being a late model five liter engine it will be the same as a 351 Windsor... Just a little more background on your problem... All could be interconnected had a friend that had a 351 in his 'stang and it backfired and had generally poor running characteristics I looked at the distributor and his wires were routed for a early small block Ford... Just some extra info... Check it out. The firing order will be1-3-7-2-6-5-4-8.


Keep the wheels spinnin' and the beavers grinnin' i'm out. :thumbsup
 

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Discussion Starter · #5 ·
thank again

the car is comin along great,thanks for the help.it still backfires i will look into the wires.But just to let you know i ran a second time at the track after new plugs oil and wires [email protected] thanks for all youre help.trying to figure out how to post time slips to prove time decrease.:drink:
 

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Discussion Starter · #6 ·
f

one of the old plugs had a broken fire stem on it. dont know what that ment?
but the car runs strong now
 

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I have been running no cats on my car for around five years and I have had no problems with backfiring... Not discounting the idea just never had that problem... Is it a definite bang coming out the exhaust? Or is it what almost sounds like a bunch of little pops when you let off the accelerator? Best way I can describe the sound... Oh well keep us all posted on how it turns out!
 

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Okay here we go take a look at these things then let me know how they work out for you... First check and make sure all your emission system is running correctly ,second adjust the carburetor or get a smaller one (600 cfm maybe) ,third look for a vacuum leak at the carb or any of the vacuum hoses around it could be a valve sticking... Fourth take a look at your firing order ,and fifth make sure your timing is correct... If none of these fixes work I would want to say maybe at some time the cam was out of your motor and was installed incorrectly so your cam timing is off... I knew a so called proffesional engine builder a few years back and he put together a 460 Ford and had the cam timing off well needless to say the darn motor backfired through the carb so much and seemed even worse under load... Well the issue was fixed and the motor ran extremely strong after that. Let me know how it works out... Good luck!
 

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firing order can be a big problem...say u got a 351 and u got the order on it for a 302...not gunna do u so good..there is a old book about as thick as a dictionary called a chiltons book...it lists about everything in your car...dunno exactly where u could find 1....maybe just search on tha net..........hope u find tha problem...c ya around
 

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First of all you can get a Chilton or a Haynes manual at any Pep Boys ,Checker Schucks Kragen ,Auto Zone ,Napa ,and at bookstores like Borders ,Barnes and Noble ,and Amazon.com... Now for the firing order all late model 302 H.Os like yours are the same has any 351W from 69 on up... 1-3-7-2-6-5-4-8. The 302 had a different firing order prior to 79 in 'Stangs (all non H.O vehicles with 302s after 79 kept the original firing order though) that was 1-5-4-2-6-3-7-8. Now that you said your car was a 83 it should have the late model firing order for a 302 H.O. If not whoever owned the car before you may have routed the wires the non H.O way... That could cause a definite backfire... Don't forget to check the other components I mentioned either good luck!:thumbsup
 

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Which one?

I just make a thread about this very topic.....firing order that is.

I have a 79 Mustang Pace Car with the 302 in it but I don't know if it's the HO or not. It's def. not stock anymore. So which of the two firing orders would i be?

1) 13726548 (HO Motors)

or

2) 15426378
 

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Lean out your fuel, The excess fuel is trapped in your exaulst system when you let off the gas and compresses the raw gas in your exaust system then goes boom...
 

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79PACER said:
I just make a thread about this very topic.....firing order that is.

I have a 79 Mustang Pace Car with the 302 in it but I don't know if it's the HO or not. It's def. not stock anymore. So which of the two firing orders would i be?

1) 13726548 (HO Motors)

or

2) 15426378
Depends on the cam... IIRC, you installed an aftermarket cam, right? The cam card should tell you which firing order to use, if not, post up the cam and I'll let ya know...
 

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Found it, thanks.
 

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my 90 5.0 backfires or rumbles and pops when I gear down and let off. I have minimal back pressure on my exhaust, 2 cats a cross over and no mufflers behind the headers. It pops small backfires until it slows down. Usually a car with a carb will do that a lot more than a fuel injected engine. My emission levels are scarey clean and it is just behaving as it should. When you let off an injected motor the fuel is pretty much shut off, on a motor with a carb you are still sucking fuel into the enging while it is trying to wind down. See if it backfires in park by just reving the engine and if so keep looking for a problem.
How does the exhaust smell. if it smells bad it could be rich or lean. At that point pull off a vacom line from the carb, if the engine picks up rpm you are fat, or rich. If it stumbles you are lean. The rpm should not change that much. Look at the plugs too to see iff they look burned or black and oily that may help too.
 

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The plugs were black. Then I cleaned them off and that's whenthe headers started glowing.
 
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