backfire through exhaust

[44070dart]

replaced 318 with 440 ..the engine ran fine on initial start up but original carb leaked gas ..NOW ..with different carb (which came off good running car) has backfire through exhaust when you give it gas ... took the valve cover off got piston up to TDC both valves closed set distributor to #1 position checked plug wires 3x's or more for correct order ..carb was rebuilt think its not lean because when choke is closed car is very rich (black smoke) ...would it backfire like this if it was to rich ?.. also the coil wires on the positive and negative sides seem to be inter changeable which wires belong on positive side which on negative there are 3 wires on coil ...help :angryfire: thanks

 

[HEMI-ITIS]

Double check the accellerator pump is squirting gas and double check your timing at idle and keep the timing light on it and bring the RPM uo to 3000,unless your distributor is locked out.:headbang:

 

[Stumper]

Could be as simple as fouled plugs too. Mine was doing it when I started it up a couple weeks ago. Changed plugs and it stopped. A couple were pretty wet when I pulled them out.

 

[Sonny Black]

same problem here...I think it turned out to be (and I hate to say this)...Bad Gas.


it (went.... BANG!!

 

[eric383]

X2 Hemi-itis...Check that the accelerator pump is squirting as soon as the throttle is opened, make sure the squirters are big enough, there aren't vacuum leaks and you have enough advance dialed into your timing.

 

[44070dart]

pulled new plugs they were wet ...installed other new one just to be sure ....timing is right on ..(bad gas ? who knows no reason to think so though)..if it idles its mostly fine ..accelerate slowly in neutral OK to a point then it start popping ..give it half throttle it continues to pop ever few second ... flip the throttle hard it really backfires ... wish I had another carb I knew was right to figure if its gas or spark causing this ..may have to take to real mechanic to have it scoped out ....disappointing ...no vacuum leaks ..will check accelerator pump.... initial timing is set at 8* advanced (don't understand advanced setting)

 

[bigmanjbmopar]

Power valve? assuming it is a Holley?

 

[Stumper]

8 degrees is not much initial timing. Try bumping it up a bit and see if it helps - with fresh plugs.

 

[44070dart]

power valve new rebuilt the carb .. had timing more advanced didn't change anything ...will check accelerator pump tomorrow ..thanks

 

[44070dart]

didn't get to it today ....one more foolish question ..if it were a lean condition causing backfire wound'nt it go away with the choke on full .. when the choke is mostly closed the car billows black smoke

 

[packerman16]

440 70dart,
this may sound crazy but how r ur plug wires and cap.
plus the fuel we get @ bargin prices doesn't even burn.

 

[44070dart]

everything is new just rebuilt ...

 

[1971RR]

Is the distributor vacuum advance or mechanical advance? I just learned something installing my new Mallory. It came from the factory with the vacuum advance module turned all the way in. I started the car without the vacuum line hooked up and it ran great. As soon as I plugged in the vacuum on the module; backfiring, loping..ran horrible. Took a 3/32 allen wrench and stuck it in the vacuum port on the distributor and turned it all the way out and then back in two turns. Ran perfect. I dont know what your carburator change was. Maybe the new one pulls better vacuum than the old one and is playing havock with the distributor. This may not be your problem but I'm just tossing it out there.

 

[cu440da]

everything is new just rebuilt ...

Dont assume just because parts are new that they are good...

I would put the timing light on each individual plug wire and watch for a steady strobe while slowly increasing revs. I went through 3 sets of brand new plugs before I got 8 good ones and had similar problems as you. Swap known good plugs to a cyl that has a funky stobe pattern. If it clears up you know plug is bad, otherwise could be the wire.

 

[moperformance]

One last thing when nothing else has helped is to remove the rocker arms and place a block of wood on each valve spring retainer and tap it a couple of times with a hammer. Don't knock the crap out of it as what your trying to do is re seat the valves IF carbon is keeping it from seating. Do a compression check first then compare your readings before and after. If nothing else, it can't hurt anything and may just might help. Good luck!

 

[44070dart]

thanks

thanks guys.... I'll check your suggestions Monday ..the vacuum advance was disconnected when we broke it in so I'll be checking that first..will update

 

[44070dart]

what a jerk

me
:iamwithstupid:
BAD GAS ... man first thing I learned when beginning to work on cars was check the easiest thing first ....I used Stable and dry gas last Nov. and have never had a problem a l l these years but that was the case this time ... you never stop learning the things you know ...thanks guys