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Author
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Topic: Car Starts But Backfires Through The Carb...
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PopTheHood
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Member # 7040
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Ive Just put a new motor in my car.. (A 331) and im having some problems with it. i got the car started and running. It runs ok but it idles like at 2500. I checked the timing and it was at 30*. so i tried to adjust it back to around 15*. the car started running really low and shi*ty. so i adjusted the idle and got the idle decent and then it backfired through the carb and died. i started it again, it ran for ten seconds backfired and died again. what could cause this? the car runs good with the timing set higher. does this motor need higher timing then my old motor? or is somthing setup wrong?
Posts: 185 | Registered: Sep 2006
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kingmoochr
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Member # 5834
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yes, you should be 25-28 or so on base timing, advancing to @32. rememeber, theres no computer advancing the timing for you, ever put a timing light on a fox with the jumper in? timing is 27 when the computer takes over
Posts: 880 | Registered: Jul 2005
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PopTheHood
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Member # 7040
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so a 331 runs at around 30* timing not 15*?
Posts: 185 | Registered: Sep 2006
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asskickn88
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Member # 4957
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If I'm reading right, you have it carbed and not injected, right? Your base timing should be around 12 degrees at idle to start with. Once you have it running correctly then you can add timing.
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Three 540 Bimmers and a 5.0 Explorer.... got a Ford back in the stable!
It's time for the country to do what Obama's own father did.
Abandon him.
Posts: 6069 | From: Rocklin, Ca | Registered: Oct 2004
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AJBlackGT
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Member # 3936
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You got the firing order correct?
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90 Notch
Posts: 1896 | From: Sacramento | Registered: Dec 2003
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PopTheHood
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Member # 7040
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so why is he saying that it should be around 30? On CHP's website they said they dynoed their motor at 30+* of timing, what are they doing different?
Posts: 185 | Registered: Sep 2006
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PopTheHood
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Member # 7040
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pretty sure that the firing order is correct. I checked it a few times. but could be wrong.
Posts: 185 | Registered: Sep 2006
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*BlueBeast88.306*
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Member # 6360
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quote:
Originally posted by AJBlackGT:
You got the firing order correct?
+1
Posts: 462 | From: Concord | Registered: Jan 2006
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86BackInBlack
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Member # 5372
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depends on what carb you got. I originaly set my demon wrong. When i actually sat down and read the instructions ![[Big Grin]](biggrin.gif) it was suppose to be set way higher than i had it. plus you got to remember to factor in you idle and mixture screws. my car was running rich as fuck and hella shitty before i correctly adjusted all of those. you get it right and that thing will scream
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http://i.imgur.com/go1nj.gif
Posts: 1438 | From: san jose | Registered: Feb 2005
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asskickn88
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Member # 4957
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quote:
Originally posted by PopTheHood:
so why is he saying that it should be around 30? On CHP's website they said they dynoed their motor at 30+* of timing, what are they doing different?
I'm sure they are talking about 30+ total degrees of advance, you should have that at 3500 RPM not at idle. At idle the timing should be around 12. It would help to post what exactly your running.... dist, ignition system, cam, carb and intake.
Where are you located?
[ December 20, 2006, 11:34 PM: Message edited by: asskickn88 ]
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Three 540 Bimmers and a 5.0 Explorer.... got a Ford back in the stable!
It's time for the country to do what Obama's own father did.
Abandon him.
Posts: 6069 | From: Rocklin, Ca | Registered: Oct 2004
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PopTheHood
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Member # 7040
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Its an Msd distributer, stock ignition system, TFS stage 1 cam Duration 275/ 279,Lift .499/ .510, 570 street avenger, and edelbrock air gap manifold. is the carb to small? i had it so i wanted to try it before i had to buy a new one
Posts: 185 | Registered: Sep 2006
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PopTheHood
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Member # 7040
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trick flow Twisted wedge aluminum heads
Posts: 185 | Registered: Sep 2006
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*BlueBeast88.306*
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Member # 6360
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Mine has a similar setup and it runs best at 20 base.
Posts: 462 | From: Concord | Registered: Jan 2006
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PopTheHood
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Member # 7040
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so where should i start the timing at? 20* and then go up from there? the higher i went the better it seemed to run. i was at 30* and it ran good. i should have tryed to lower its idle
Posts: 185 | Registered: Sep 2006
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*BlueBeast88.306*
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Member # 6360
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Were you at 30 with the advance disconnected at idle, because if you had the advance hooked up and saw 30 you are probably at around 20-22 base?
Are you running elctronic or mechanical ignition with your carb setup?
Posts: 462 | From: Concord | Registered: Jan 2006
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PopTheHood
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Member # 7040
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Whatever came stock on the car. the distributer did have the vaccume line hooked up to it. im supposed to take that off when i do the timing right.. I forgot to. you think thats my problem?
Posts: 185 | Registered: Sep 2006
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*BlueBeast88.306*
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Member # 6360
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So, with the vacuum line disconnected and capped your timming is probably around 20-22. Thats where mine likes to run. Make sure everything else is right and broke in for a while before you run that thing to hard and screw it up.
Posts: 462 | From: Concord | Registered: Jan 2006
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v-town coupe
fordologist
Member # 2771
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yeah make sure that firing order is right cause some people tend to get firing order wrong cause stock 5.0 with a roller use a 351w firing order and im sure if ur using a trick flow cam its the same as what stock firing order is. of course if someone would back me up onthis that would be cool but im almost positive. and just my .02 but with a carb u should start off with about 12 deg in. timing and a around 30-33 total just to throw a # out there u can always add more later! and the carb being too small wouldnt cause it to do what ur describing but with a 331 and alum heads and what not a 600 dp or 650 may be more at home on top of that u will notice not as much top end with a 570. jus my .02
[ December 22, 2006, 01:17 PM: Message edited by: v-town coupe ]
Posts: 4597 | From: the V-town | Registered: May 2003
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PopTheHood
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Member # 7040
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i got the car to run decent but when it gets warmed up the rpm's raise and lower between 800 and 2000 and then the cars dies and backfires through the carb. it works good untill it gets warm.
Posts: 185 | Registered: Sep 2006
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v-town coupe
fordologist
Member # 2771
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i dont know if he'll take it on but if u cant get it tuned correctly u could send john b a pm now that hes back hes only up in fairfield.
Posts: 4597 | From: the V-town | Registered: May 2003
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CMELEVU
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Member # 2563
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as far as the timing, i think you would have to set it without the vac line hooked up to the dist. that would be your base. as far as it surging and dying after it warms up you might have to set your idle screws on the carb. Its been a while since i messed around with a carb but i kinda had the same mess with my 65 when i swapped cams. also make sure that your not a tooth off on the dist. i was on my 91 when i dropped in the new motor. car started up ran fine with the timing marks at 30 base. but giving it any gas it would backfire and run funny. took a while to figure that one out. ![[Embarrassed]](redface.gif)
Posts: 201 | From: Marysville | Registered: Mar 2003
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1988Stang
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Member # 6280
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If you have a carb setup on a motor, the myth of having the vacuum line disconnected is not true. I am sure most of you think it is, but it's not. When you are timing your motor at idle you shouldn't have any vaccum going to the distributor period, as soon as you give it some gas then the vacuum advance should engage.
So what you do is start the car, then pull the vacuum live off the distributor, if the motor starts to run differently then you have your vacuum line hooked up to a constant vacuum and not an advance vacuum, that will cause your motor to run wierd and not idle properly. Your vacuum constantly changes as your motor idles, that could be your idle problem.
As for the timing part, with a carb setup your initial timing should be somewhere from 10 degrees to 15 degrees, and total timing should be around 32 to 36 degrees. I definetly wouldn't run over 36 degrees of timing on your motor. You also have to remember that you have a stroker motor. Running to much timing can crack a piston or cause serious problems.
Also, how much power is your motor supposed to have? If you don't have enough carb your motor can have a lean pop, which would cause back firing and popping out the exhaust and out of the carb.
Also, if you have some tight exhaust valves your motor will exhaust out of the carb because the valve isn't opening properly, the exhaust has to exit somewhere, so it goes out the carb.
If you have any questions you can call me and i can talk you through it. Also what city do you live in, i live in Petaluma, i might be able to come take a look at it in person. My number is (707)478-4463 Matt
Posts: 161 | From: Petaluma | Registered: Dec 2005
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1988Stang
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Member # 6280
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Forgot to state somthing, When you are doing total timing, like running your motor at 3,000 rpms, then you have to disconnect the vaccum line because you motor will be producing a lot of vacuum and give you false readings. But when you do initial timing you shouldn't have the vacuum line from the distributor to a constant vaccum source anyway so it doesn't matter wheather it is hooked up or not.
Posts: 161 | From: Petaluma | Registered: Dec 2005
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PopTheHood
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Member # 7040
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I found out what the problem was. It was my fuel pump. I hooked up a pressure guage to it and it was only puttin out right under 5 psi at idle. I got a new one. I put it on and it puts out 8 psi at idle. from there i set the timing then i did the float adjustments, then the mixture screws, then the timing again. my car will not run with the timing close to what it used to be. (10-15)
I have it set to 28* and it runs good and hard all the way through the rpm range. It idles nice, has good throttle responce, doesn't over heat or anything. i tryed to bring the timing down. starts backfiring, running like ****, took it for a drive and the car barely wanted to go anywhere. So i think the timing for 331's should be in the 20's unlike what some people have been saying. thats just my opinion though.
My neighbor has an old corvette. he had his timing and everything set to 8*. then he changed his motor and he said it had to be set at 22* to get his car to run good.
So 28* works for my car,... maybe it depends on the cam, intake, heads and whatever else you got.
Thanks for all of your help.
If there is anything that you have to say about what i said above please do so. arguements are welcome too.
Posts: 185 | Registered: Sep 2006
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