carbuerator backfire

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Dec 3, 2006 | 01:12 PM

gearhed1971

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From: Little Falls,New York

carbuerator backfire

my carb is backfiring and doesn't run very well first thing in the morning.I have a problem with it backfiring through the carb when cold .Any body know why?

Dec 3, 2006 | 01:14 PM

LxMan1

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From: Louisville,Ky.

My first guess would be that the choke isn't working properly. Also the timing might be a little slow.

Dec 3, 2006 | 01:56 PM

gearhed1971

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From: Little Falls,New York

The choke isn't even hooked up.It backfires when it starts a few times,then once down the road.I sprayed carb medic in it and revved the engine a few times,and the carb backfired every time.I though about putting a hand choke on it,will this help?By the way,its a motorcraft two barrel on a '76 390,egr disconnected

Last edited by gearhed1971; Dec 3, 2006 at 02:00 PM. Reason: left out info

Dec 4, 2006 | 09:05 PM

WarWagon

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If the choke isn't hooked up, you are getting a lean backfire in the intake. Hook up the choke. You could always ignore that and cook your hotdogs on the burning air filter.

Feb 5, 2007 | 09:18 PM

cohammer

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backfires through carb

having a problen with my 300 inline 6 goes pop , pop , seems like each time it hits a certain cyl. I do see some exhust leaks on out going . ran fine until took it out of truck , when putting motor back in truck it fell over changed rotor cap and button they were broken. noticed when rotor cap is off I can turn on switch take the plate down in dis. and shake and can see spark. think bottom of disb cuold be damanged also? thanks for any help. also can not seem to get all vacumn hoses put back right

Feb 6, 2007 | 12:24 AM

LxMan1

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From: Louisville,Ky.

Cohammer, Does it have points or electronic ignition? If it is close to the magnetic pick up, it may spark when the advance plate is moved. This is normal. Sounds like you have a cracked spark plug.

Apr 1, 2007 | 11:09 AM

cohammer

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I'll look for a cracked plug I have just about given up on this motor it has dura spark it is a 1982 4.9 , I have changed the wires ,carb,dura spark,and the stator and I have found when I un plug a vacumn hose it does better when it sucks more air. The motor no longer has a vac pump on it the person I bought it from had taken it off. I wish people would leave factory vac alone.

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Apr 3, 2007 | 03:33 PM

cohammer

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I think I know what to do but just making sure, I would take out each plug preform a comp. test and see if they each hold?

Apr 3, 2007 | 08:03 PM

#10

fmc400

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From: Austin, TX

Quote:

Originally Posted by cohammer

I think I know what to do but just making sure, I would take out each plug preform a comp. test and see if they each hold?

That's exactly right. You need to do a compression test on each cylinder. If you find any cylinder that is way lower than the others, you need to do a leakdown on that particular cylinder to find where you're losing compression. Usually you want all of the cylinders within 10% of each other. Uniformity among cylinder is more important than the actual numbers. Also, as a general rule of thumb, if a cylinder is low on compression, you can squirt some motor oil into the spark plug hole with a squirt can and check the compression again. If the compression isn't any better than the problem is most likely in the valves...if the compression does get better than the leak is most likely worn rings. However, if you're getting a lot of backfires and it's compression-related then it's valves.

Last edited by fmc400; Apr 3, 2007 at 08:09 PM.

Apr 7, 2007 | 09:38 PM

#11

cohammer

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push rod

need some help with my 82, 4.9 took the valve cover off to see why it might be backfiring and the #3 pusr rod and the #4 push rod are droped down and do not move as the engine is cranked ,how bad is this?

Apr 7, 2007 | 10:57 PM

#12

LxMan1

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From: Louisville,Ky.

Sounds like either the pushrod has bent or a lifter has gone. You can pull a cam cover off of the side of the block and inspect the lifter/pushrod.

Apr 8, 2007 | 08:10 AM

#13

cohammer

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I will give that a try , I had the side panel off not long ago and looked it over but at the time I was just looking for a rattle , The motor had been rebuilt before I bought it last year but has never been just right as far as the push rods . Thanks for the info I hope I can repair it without taking the motor back out.