carb/timing issue when cold

[jct]

it tends to backfire thru the carb and dies/stalls out when the motor is cold, it's fine soon as it's up to temp.

my timing is set to around 7.5° btc, point gap is around .015, dwell is around 26°

how do i stop it from being problematic when it's cold? i will be rebuilding the carb soon...

 

[70bigblockdodge]

Sounds like choke is inoperative or not adjusted properly.

 

[jct]

kind of figured that was the case... i will get around to checking it out

 

[jct]

the idle cam was out of wack, got that taken care of, cleaned the choke spring, and that is still set, correctly, adjusted the timing to 9 degrees btdc, reset the fast and curb idle screws to around what the fsm says, seems to be happier car now! starts right up, with no hicups

 

[jct]

found out i have a bum choke shaft, which ever hack job company rebuilt the carb, nice Q.C. there makes the choke stick open and won't reset when i get back in the car when it's cold... will be fixing that soon and the choke plate screws were loose o_0

 

[Big_John]

Make sure the choke plate screws are staked so they can't back out all the way and fall into the engine.

 

[jct]

they are staked from what i saw

 

[jct]

replaced the airhorn off the parts carb. so the choke half of it is fully functional, rebuilt the bottom half of the old carb... still back firing thru the intake. do i need to richen it up a air or lean it out some

 

[jct]

if i'm taking it easy with the acceleration it's fine drove around town to the highway. soon as i got to the on-ramp and on tromped on it just to get up to speed... back fired thru the intake after it was nearly warmed up which was about 5 minutes later.

which got me thinking it might be a timing/ignition issue, mech/vacuum advance issues and my dwell is a couple degrees below spec

it does feel like there is a slight surge at highway speeds too

 

[Yatzee]

Sounds as if your totally original under the hood. Some things to consider: check the operation of the accelerator pump on the carb, secondary operation weather mechanical or vacuum, dwell gap right on, distributor cap clean and on tight and all ignition wires seated properly at the plugs and the cap. Using a hand vacuum gauge you can check the advance pot while the engines running. I run 16 degrees advance at idle even though the manual says 12. Must be today's gas because the engine runs flawless at this setting. If you backfiring though the carb it has to be a timing issue and basically one ore more valves aren't completely seated when the cylinder charge is ignited. You may also have a bum coil so you need to measure the coil's resistance to be sure.

 

[jct]

the carb is not original, it's some reman carter bbd which i rebuilt this past weekend and replaced the airhorn. i changed the plugs, wires, cap and rotor.

i will mess with the timing and check the coil resistance this weekend

and the back firing sounds like it's coming from cylinder #7

 

[commando1]

and the back firing sounds like it's coming from cylinder #7

Seriously? Good ear....

 

[jct]

i'm taking crap shots on which it is i just know it's on the odd number cylinder side of the block

 

[jct]

replaced the dist with a reman, set the points to what everybody sets them at and the dwell is within spec timing set at 10 btdc car seems to be running like a champ and starts right up. i am so ready for that 4bbl carb now

still haven't got around to checking the resistance in the coil yet ran out of time today

 

[commando1]

So, it wasn't #7...

Seriously, glad its running good. I think the coil is a moot point now.

 

[jct]

i still need further test when the car is cold and work from there

 

[70bigblockdodge]

A weak coil is usually affected by heat puts out less voltage. I have had one that would idle well, steady state cruise well, sputter and run terrible as the load went up.

 

[jct]

that's one of test jn the service manual says to do, test it hot and cold

 

[jct]

was about a quart low on oil and all i had on hand was some marvel mystery oil it seem to clean up some gunk from where ever the problem was but it reduced the back firing quite a bit i was trying to get it to back fire by driving it hard. even managed to lay a single strip of rubber on the ground with 2.76:1 o_0 (i was under the impression that it couldn't be done, guess i proved that wrong) oops. but soon as i was turning right it back fired twice.

btw it's most likely coming from cylinder #5 that's the only plug that's most fouled up with oil goo

 

[jct]

Have not given up on finding the issue. Heads rebuilt, new exhaust, new timing chain.

Drove my car around a few twisty back roads and pretty much made it make a popping sound out of the left exhaust manifold area...

I do believe i narrowed it down to somewhere in the carburetor